MFV r329807:

[FreeBSD/FreeBSD.git] / sys / dev / hwpmc / hwpmc_mod.c

/*-
 * SPDX-License-Identifier: BSD-2-Clause-FreeBSD
 *
 * Copyright (c) 2003-2008 Joseph Koshy
 * Copyright (c) 2007 The FreeBSD Foundation
 * All rights reserved.
 *
 * Portions of this software were developed by A. Joseph Koshy under
 * sponsorship from the FreeBSD Foundation and Google, Inc.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 * 1. Redistributions of source code must retain the above copyright
 *    notice, this list of conditions and the following disclaimer.
 * 2. Redistributions in binary form must reproduce the above copyright
 *    notice, this list of conditions and the following disclaimer in the
 *    documentation and/or other materials provided with the distribution.
 *
 * THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND
 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
 * ARE DISCLAIMED.  IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
 * SUCH DAMAGE.
 *
 */

#include <sys/cdefs.h>
__FBSDID("$FreeBSD$");

#include <sys/param.h>
#include <sys/eventhandler.h>
#include <sys/jail.h>
#include <sys/kernel.h>
#include <sys/kthread.h>
#include <sys/limits.h>
#include <sys/lock.h>
#include <sys/malloc.h>
#include <sys/module.h>
#include <sys/mount.h>
#include <sys/mutex.h>
#include <sys/pmc.h>
#include <sys/pmckern.h>
#include <sys/pmclog.h>
#include <sys/priv.h>
#include <sys/proc.h>
#include <sys/queue.h>
#include <sys/resourcevar.h>
#include <sys/rwlock.h>
#include <sys/sched.h>
#include <sys/signalvar.h>
#include <sys/smp.h>
#include <sys/sx.h>
#include <sys/sysctl.h>
#include <sys/sysent.h>
#include <sys/systm.h>
#include <sys/vnode.h>

#include <sys/linker.h>         /* needs to be after <sys/malloc.h> */

#include <machine/atomic.h>
#include <machine/md_var.h>

#include <vm/vm.h>
#include <vm/vm_extern.h>
#include <vm/pmap.h>
#include <vm/vm_map.h>
#include <vm/vm_object.h>

#include "hwpmc_soft.h"

/*
 * Types
 */

enum pmc_flags {
        PMC_FLAG_NONE     = 0x00, /* do nothing */
        PMC_FLAG_REMOVE   = 0x01, /* atomically remove entry from hash */
        PMC_FLAG_ALLOCATE = 0x02, /* add entry to hash if not found */
};

/*
 * The offset in sysent where the syscall is allocated.
 */

static int pmc_syscall_num = NO_SYSCALL;
struct pmc_cpu          **pmc_pcpu;      /* per-cpu state */
pmc_value_t             *pmc_pcpu_saved; /* saved PMC values: CSW handling */

#define PMC_PCPU_SAVED(C,R)     pmc_pcpu_saved[(R) + md->pmd_npmc*(C)]

struct mtx_pool         *pmc_mtxpool;
static int              *pmc_pmcdisp;    /* PMC row dispositions */

#define PMC_ROW_DISP_IS_FREE(R)         (pmc_pmcdisp[(R)] == 0)
#define PMC_ROW_DISP_IS_THREAD(R)       (pmc_pmcdisp[(R)] > 0)
#define PMC_ROW_DISP_IS_STANDALONE(R)   (pmc_pmcdisp[(R)] < 0)

#define PMC_MARK_ROW_FREE(R) do {                                         \
        pmc_pmcdisp[(R)] = 0;                                             \
} while (0)

#define PMC_MARK_ROW_STANDALONE(R) do {                                   \
        KASSERT(pmc_pmcdisp[(R)] <= 0, ("[pmc,%d] row disposition error", \
                    __LINE__));                                           \
        atomic_add_int(&pmc_pmcdisp[(R)], -1);                            \
        KASSERT(pmc_pmcdisp[(R)] >= (-pmc_cpu_max_active()),              \
                ("[pmc,%d] row disposition error", __LINE__));            \
} while (0)

#define PMC_UNMARK_ROW_STANDALONE(R) do {                                 \
        atomic_add_int(&pmc_pmcdisp[(R)], 1);                             \
        KASSERT(pmc_pmcdisp[(R)] <= 0, ("[pmc,%d] row disposition error", \
                    __LINE__));                                           \
} while (0)

#define PMC_MARK_ROW_THREAD(R) do {                                       \
        KASSERT(pmc_pmcdisp[(R)] >= 0, ("[pmc,%d] row disposition error", \
                    __LINE__));                                           \
        atomic_add_int(&pmc_pmcdisp[(R)], 1);                             \
} while (0)

#define PMC_UNMARK_ROW_THREAD(R) do {                                     \
        atomic_add_int(&pmc_pmcdisp[(R)], -1);                            \
        KASSERT(pmc_pmcdisp[(R)] >= 0, ("[pmc,%d] row disposition error", \
                    __LINE__));                                           \
} while (0)


/* various event handlers */
static eventhandler_tag pmc_exit_tag, pmc_fork_tag, pmc_kld_load_tag,
    pmc_kld_unload_tag;

/* Module statistics */
struct pmc_op_getdriverstats pmc_stats;

/* Machine/processor dependent operations */
static struct pmc_mdep  *md;

/*
 * Hash tables mapping owner processes and target threads to PMCs.
 */

struct mtx pmc_processhash_mtx;         /* spin mutex */
static u_long pmc_processhashmask;
static LIST_HEAD(pmc_processhash, pmc_process)  *pmc_processhash;

/*
 * Hash table of PMC owner descriptors.  This table is protected by
 * the shared PMC "sx" lock.
 */

static u_long pmc_ownerhashmask;
static LIST_HEAD(pmc_ownerhash, pmc_owner)      *pmc_ownerhash;

/*
 * List of PMC owners with system-wide sampling PMCs.
 */

static LIST_HEAD(, pmc_owner)                   pmc_ss_owners;


/*
 * A map of row indices to classdep structures.
 */
static struct pmc_classdep **pmc_rowindex_to_classdep;

/*
 * Prototypes
 */

#ifdef  HWPMC_DEBUG
static int      pmc_debugflags_sysctl_handler(SYSCTL_HANDLER_ARGS);
static int      pmc_debugflags_parse(char *newstr, char *fence);
#endif

static int      load(struct module *module, int cmd, void *arg);
static int      pmc_attach_process(struct proc *p, struct pmc *pm);
static struct pmc *pmc_allocate_pmc_descriptor(void);
static struct pmc_owner *pmc_allocate_owner_descriptor(struct proc *p);
static int      pmc_attach_one_process(struct proc *p, struct pmc *pm);
static int      pmc_can_allocate_rowindex(struct proc *p, unsigned int ri,
    int cpu);
static int      pmc_can_attach(struct pmc *pm, struct proc *p);
static void     pmc_capture_user_callchain(int cpu, int soft, struct trapframe *tf);
static void     pmc_cleanup(void);
static int      pmc_detach_process(struct proc *p, struct pmc *pm);
static int      pmc_detach_one_process(struct proc *p, struct pmc *pm,
    int flags);
static void     pmc_destroy_owner_descriptor(struct pmc_owner *po);
static void     pmc_destroy_pmc_descriptor(struct pmc *pm);
static struct pmc_owner *pmc_find_owner_descriptor(struct proc *p);
static int      pmc_find_pmc(pmc_id_t pmcid, struct pmc **pm);
static struct pmc *pmc_find_pmc_descriptor_in_process(struct pmc_owner *po,
    pmc_id_t pmc);
static struct pmc_process *pmc_find_process_descriptor(struct proc *p,
    uint32_t mode);
static void     pmc_force_context_switch(void);
static void     pmc_link_target_process(struct pmc *pm,
    struct pmc_process *pp);
static void     pmc_log_all_process_mappings(struct pmc_owner *po);
static void     pmc_log_kernel_mappings(struct pmc *pm);
static void     pmc_log_process_mappings(struct pmc_owner *po, struct proc *p);
static void     pmc_maybe_remove_owner(struct pmc_owner *po);
static void     pmc_process_csw_in(struct thread *td);
static void     pmc_process_csw_out(struct thread *td);
static void     pmc_process_exit(void *arg, struct proc *p);
static void     pmc_process_fork(void *arg, struct proc *p1,
    struct proc *p2, int n);
static void     pmc_process_samples(int cpu, int soft);
static void     pmc_release_pmc_descriptor(struct pmc *pmc);
static void     pmc_remove_owner(struct pmc_owner *po);
static void     pmc_remove_process_descriptor(struct pmc_process *pp);
static void     pmc_restore_cpu_binding(struct pmc_binding *pb);
static void     pmc_save_cpu_binding(struct pmc_binding *pb);
static void     pmc_select_cpu(int cpu);
static int      pmc_start(struct pmc *pm);
static int      pmc_stop(struct pmc *pm);
static int      pmc_syscall_handler(struct thread *td, void *syscall_args);
static void     pmc_unlink_target_process(struct pmc *pmc,
    struct pmc_process *pp);
static int generic_switch_in(struct pmc_cpu *pc, struct pmc_process *pp);
static int generic_switch_out(struct pmc_cpu *pc, struct pmc_process *pp);
static struct pmc_mdep *pmc_generic_cpu_initialize(void);
static void pmc_generic_cpu_finalize(struct pmc_mdep *md);

/*
 * Kernel tunables and sysctl(8) interface.
 */

SYSCTL_DECL(_kern_hwpmc);

static int pmc_callchaindepth = PMC_CALLCHAIN_DEPTH;
SYSCTL_INT(_kern_hwpmc, OID_AUTO, callchaindepth, CTLFLAG_RDTUN,
    &pmc_callchaindepth, 0, "depth of call chain records");

#ifdef  HWPMC_DEBUG
struct pmc_debugflags pmc_debugflags = PMC_DEBUG_DEFAULT_FLAGS;
char    pmc_debugstr[PMC_DEBUG_STRSIZE];
TUNABLE_STR(PMC_SYSCTL_NAME_PREFIX "debugflags", pmc_debugstr,
    sizeof(pmc_debugstr));
SYSCTL_PROC(_kern_hwpmc, OID_AUTO, debugflags,
    CTLTYPE_STRING | CTLFLAG_RWTUN | CTLFLAG_NOFETCH,
    0, 0, pmc_debugflags_sysctl_handler, "A", "debug flags");
#endif

/*
 * kern.hwpmc.hashrows -- determines the number of rows in the
 * of the hash table used to look up threads
 */

static int pmc_hashsize = PMC_HASH_SIZE;
SYSCTL_INT(_kern_hwpmc, OID_AUTO, hashsize, CTLFLAG_RDTUN,
    &pmc_hashsize, 0, "rows in hash tables");

/*
 * kern.hwpmc.nsamples --- number of PC samples/callchain stacks per CPU
 */

static int pmc_nsamples = PMC_NSAMPLES;
SYSCTL_INT(_kern_hwpmc, OID_AUTO, nsamples, CTLFLAG_RDTUN,
    &pmc_nsamples, 0, "number of PC samples per CPU");


/*
 * kern.hwpmc.mtxpoolsize -- number of mutexes in the mutex pool.
 */

static int pmc_mtxpool_size = PMC_MTXPOOL_SIZE;
SYSCTL_INT(_kern_hwpmc, OID_AUTO, mtxpoolsize, CTLFLAG_RDTUN,
    &pmc_mtxpool_size, 0, "size of spin mutex pool");


/*
 * security.bsd.unprivileged_syspmcs -- allow non-root processes to
 * allocate system-wide PMCs.
 *
 * Allowing unprivileged processes to allocate system PMCs is convenient
 * if system-wide measurements need to be taken concurrently with other
 * per-process measurements.  This feature is turned off by default.
 */

static int pmc_unprivileged_syspmcs = 0;
SYSCTL_INT(_security_bsd, OID_AUTO, unprivileged_syspmcs, CTLFLAG_RWTUN,
    &pmc_unprivileged_syspmcs, 0,
    "allow unprivileged process to allocate system PMCs");

/*
 * Hash function.  Discard the lower 2 bits of the pointer since
 * these are always zero for our uses.  The hash multiplier is
 * round((2^LONG_BIT) * ((sqrt(5)-1)/2)).
 */

#if     LONG_BIT == 64
#define _PMC_HM         11400714819323198486u
#elif   LONG_BIT == 32
#define _PMC_HM         2654435769u
#else
#error  Must know the size of 'long' to compile
#endif

#define PMC_HASH_PTR(P,M)       ((((unsigned long) (P) >> 2) * _PMC_HM) & (M))

/*
 * Syscall structures
 */

/* The `sysent' for the new syscall */
static struct sysent pmc_sysent = {
        .sy_narg =      2,
        .sy_call =      pmc_syscall_handler,
};

static struct syscall_module_data pmc_syscall_mod = {
        .chainevh =     load,
        .chainarg =     NULL,
        .offset =       &pmc_syscall_num,
        .new_sysent =   &pmc_sysent,
        .old_sysent =   { .sy_narg = 0, .sy_call = NULL },
        .flags =        SY_THR_STATIC_KLD,
};

static moduledata_t pmc_mod = {
        .name =         PMC_MODULE_NAME,
        .evhand =       syscall_module_handler,
        .priv =         &pmc_syscall_mod,
};

#ifdef EARLY_AP_STARTUP
DECLARE_MODULE(pmc, pmc_mod, SI_SUB_SYSCALLS, SI_ORDER_ANY);
#else
DECLARE_MODULE(pmc, pmc_mod, SI_SUB_SMP, SI_ORDER_ANY);
#endif
MODULE_VERSION(pmc, PMC_VERSION);

#ifdef  HWPMC_DEBUG
enum pmc_dbgparse_state {
        PMCDS_WS,               /* in whitespace */
        PMCDS_MAJOR,            /* seen a major keyword */
        PMCDS_MINOR
};

static int
pmc_debugflags_parse(char *newstr, char *fence)
{
        char c, *p, *q;
        struct pmc_debugflags *tmpflags;
        int error, found, *newbits, tmp;
        size_t kwlen;

        tmpflags = malloc(sizeof(*tmpflags), M_PMC, M_WAITOK|M_ZERO);

        p = newstr;
        error = 0;

        for (; p < fence && (c = *p); p++) {

                /* skip white space */
                if (c == ' ' || c == '\t')
                        continue;

                /* look for a keyword followed by "=" */
                for (q = p; p < fence && (c = *p) && c != '='; p++)
                        ;
                if (c != '=') {
                        error = EINVAL;
                        goto done;
                }

                kwlen = p - q;
                newbits = NULL;

                /* lookup flag group name */
#define DBG_SET_FLAG_MAJ(S,F)                                           \
                if (kwlen == sizeof(S)-1 && strncmp(q, S, kwlen) == 0)  \
                        newbits = &tmpflags->pdb_ ## F;

                DBG_SET_FLAG_MAJ("cpu",         CPU);
                DBG_SET_FLAG_MAJ("csw",         CSW);
                DBG_SET_FLAG_MAJ("logging",     LOG);
                DBG_SET_FLAG_MAJ("module",      MOD);
                DBG_SET_FLAG_MAJ("md",          MDP);
                DBG_SET_FLAG_MAJ("owner",       OWN);
                DBG_SET_FLAG_MAJ("pmc",         PMC);
                DBG_SET_FLAG_MAJ("process",     PRC);
                DBG_SET_FLAG_MAJ("sampling",    SAM);

                if (newbits == NULL) {
                        error = EINVAL;
                        goto done;
                }

                p++;            /* skip the '=' */

                /* Now parse the individual flags */
                tmp = 0;
        newflag:
                for (q = p; p < fence && (c = *p); p++)
                        if (c == ' ' || c == '\t' || c == ',')
                                break;

                /* p == fence or c == ws or c == "," or c == 0 */

                if ((kwlen = p - q) == 0) {
                        *newbits = tmp;
                        continue;
                }

                found = 0;
#define DBG_SET_FLAG_MIN(S,F)                                           \
                if (kwlen == sizeof(S)-1 && strncmp(q, S, kwlen) == 0)  \
                        tmp |= found = (1 << PMC_DEBUG_MIN_ ## F)

                /* a '*' denotes all possible flags in the group */
                if (kwlen == 1 && *q == '*')
                        tmp = found = ~0;
                /* look for individual flag names */
                DBG_SET_FLAG_MIN("allocaterow", ALR);
                DBG_SET_FLAG_MIN("allocate",    ALL);
                DBG_SET_FLAG_MIN("attach",      ATT);
                DBG_SET_FLAG_MIN("bind",        BND);
                DBG_SET_FLAG_MIN("config",      CFG);
                DBG_SET_FLAG_MIN("exec",        EXC);
                DBG_SET_FLAG_MIN("exit",        EXT);
                DBG_SET_FLAG_MIN("find",        FND);
                DBG_SET_FLAG_MIN("flush",       FLS);
                DBG_SET_FLAG_MIN("fork",        FRK);
                DBG_SET_FLAG_MIN("getbuf",      GTB);
                DBG_SET_FLAG_MIN("hook",        PMH);
                DBG_SET_FLAG_MIN("init",        INI);
                DBG_SET_FLAG_MIN("intr",        INT);
                DBG_SET_FLAG_MIN("linktarget",  TLK);
                DBG_SET_FLAG_MIN("mayberemove", OMR);
                DBG_SET_FLAG_MIN("ops",         OPS);
                DBG_SET_FLAG_MIN("read",        REA);
                DBG_SET_FLAG_MIN("register",    REG);
                DBG_SET_FLAG_MIN("release",     REL);
                DBG_SET_FLAG_MIN("remove",      ORM);
                DBG_SET_FLAG_MIN("sample",      SAM);
                DBG_SET_FLAG_MIN("scheduleio",  SIO);
                DBG_SET_FLAG_MIN("select",      SEL);
                DBG_SET_FLAG_MIN("signal",      SIG);
                DBG_SET_FLAG_MIN("swi",         SWI);
                DBG_SET_FLAG_MIN("swo",         SWO);
                DBG_SET_FLAG_MIN("start",       STA);
                DBG_SET_FLAG_MIN("stop",        STO);
                DBG_SET_FLAG_MIN("syscall",     PMS);
                DBG_SET_FLAG_MIN("unlinktarget", TUL);
                DBG_SET_FLAG_MIN("write",       WRI);
                if (found == 0) {
                        /* unrecognized flag name */
                        error = EINVAL;
                        goto done;
                }

                if (c == 0 || c == ' ' || c == '\t') {  /* end of flag group */
                        *newbits = tmp;
                        continue;
                }

                p++;
                goto newflag;
        }

        /* save the new flag set */
        bcopy(tmpflags, &pmc_debugflags, sizeof(pmc_debugflags));

 done:
        free(tmpflags, M_PMC);
        return error;
}

static int
pmc_debugflags_sysctl_handler(SYSCTL_HANDLER_ARGS)
{
        char *fence, *newstr;
        int error;
        unsigned int n;

        (void) arg1; (void) arg2; /* unused parameters */

        n = sizeof(pmc_debugstr);
        newstr = malloc(n, M_PMC, M_WAITOK|M_ZERO);
        (void) strlcpy(newstr, pmc_debugstr, n);

        error = sysctl_handle_string(oidp, newstr, n, req);

        /* if there is a new string, parse and copy it */
        if (error == 0 && req->newptr != NULL) {
                fence = newstr + (n < req->newlen ? n : req->newlen + 1);
                if ((error = pmc_debugflags_parse(newstr, fence)) == 0)
                        (void) strlcpy(pmc_debugstr, newstr,
                            sizeof(pmc_debugstr));
        }

        free(newstr, M_PMC);

        return error;
}
#endif

/*
 * Map a row index to a classdep structure and return the adjusted row
 * index for the PMC class index.
 */
static struct pmc_classdep *
pmc_ri_to_classdep(struct pmc_mdep *md, int ri, int *adjri)
{
        struct pmc_classdep *pcd;

        (void) md;

        KASSERT(ri >= 0 && ri < md->pmd_npmc,
            ("[pmc,%d] illegal row-index %d", __LINE__, ri));

        pcd = pmc_rowindex_to_classdep[ri];

        KASSERT(pcd != NULL,
            ("[pmc,%d] ri %d null pcd", __LINE__, ri));

        *adjri = ri - pcd->pcd_ri;

        KASSERT(*adjri >= 0 && *adjri < pcd->pcd_num,
            ("[pmc,%d] adjusted row-index %d", __LINE__, *adjri));

        return (pcd);
}

/*
 * Concurrency Control
 *
 * The driver manages the following data structures:
 *
 *   - target process descriptors, one per target process
 *   - owner process descriptors (and attached lists), one per owner process
 *   - lookup hash tables for owner and target processes
 *   - PMC descriptors (and attached lists)
 *   - per-cpu hardware state
 *   - the 'hook' variable through which the kernel calls into
 *     this module
 *   - the machine hardware state (managed by the MD layer)
 *
 * These data structures are accessed from:
 *
 * - thread context-switch code
 * - interrupt handlers (possibly on multiple cpus)
 * - kernel threads on multiple cpus running on behalf of user
 *   processes doing system calls
 * - this driver's private kernel threads
 *
 * = Locks and Locking strategy =
 *
 * The driver uses four locking strategies for its operation:
 *
 * - The global SX lock "pmc_sx" is used to protect internal
 *   data structures.
 *
 *   Calls into the module by syscall() start with this lock being
 *   held in exclusive mode.  Depending on the requested operation,
 *   the lock may be downgraded to 'shared' mode to allow more
 *   concurrent readers into the module.  Calls into the module from
 *   other parts of the kernel acquire the lock in shared mode.
 *
 *   This SX lock is held in exclusive mode for any operations that
 *   modify the linkages between the driver's internal data structures.
 *
 *   The 'pmc_hook' function pointer is also protected by this lock.
 *   It is only examined with the sx lock held in exclusive mode.  The
 *   kernel module is allowed to be unloaded only with the sx lock held
 *   in exclusive mode.  In normal syscall handling, after acquiring the
 *   pmc_sx lock we first check that 'pmc_hook' is non-null before
 *   proceeding.  This prevents races between the thread unloading the module
 *   and other threads seeking to use the module.
 *
 * - Lookups of target process structures and owner process structures
 *   cannot use the global "pmc_sx" SX lock because these lookups need
 *   to happen during context switches and in other critical sections
 *   where sleeping is not allowed.  We protect these lookup tables
 *   with their own private spin-mutexes, "pmc_processhash_mtx" and
 *   "pmc_ownerhash_mtx".
 *
 * - Interrupt handlers work in a lock free manner.  At interrupt
 *   time, handlers look at the PMC pointer (phw->phw_pmc) configured
 *   when the PMC was started.  If this pointer is NULL, the interrupt
 *   is ignored after updating driver statistics.  We ensure that this
 *   pointer is set (using an atomic operation if necessary) before the
 *   PMC hardware is started.  Conversely, this pointer is unset atomically
 *   only after the PMC hardware is stopped.
 *
 *   We ensure that everything needed for the operation of an
 *   interrupt handler is available without it needing to acquire any
 *   locks.  We also ensure that a PMC's software state is destroyed only
 *   after the PMC is taken off hardware (on all CPUs).
 *
 * - Context-switch handling with process-private PMCs needs more
 *   care.
 *
 *   A given process may be the target of multiple PMCs.  For example,
 *   PMCATTACH and PMCDETACH may be requested by a process on one CPU
 *   while the target process is running on another.  A PMC could also
 *   be getting released because its owner is exiting.  We tackle
 *   these situations in the following manner:
 *
 *   - each target process structure 'pmc_process' has an array
 *     of 'struct pmc *' pointers, one for each hardware PMC.
 *
 *   - At context switch IN time, each "target" PMC in RUNNING state
 *     gets started on hardware and a pointer to each PMC is copied into
 *     the per-cpu phw array.  The 'runcount' for the PMC is
 *     incremented.
 *
 *   - At context switch OUT time, all process-virtual PMCs are stopped
 *     on hardware.  The saved value is added to the PMCs value field
 *     only if the PMC is in a non-deleted state (the PMCs state could
 *     have changed during the current time slice).
 *
 *     Note that since in-between a switch IN on a processor and a switch
 *     OUT, the PMC could have been released on another CPU.  Therefore
 *     context switch OUT always looks at the hardware state to turn
 *     OFF PMCs and will update a PMC's saved value only if reachable
 *     from the target process record.
 *
 *   - OP PMCRELEASE could be called on a PMC at any time (the PMC could
 *     be attached to many processes at the time of the call and could
 *     be active on multiple CPUs).
 *
 *     We prevent further scheduling of the PMC by marking it as in
 *     state 'DELETED'.  If the runcount of the PMC is non-zero then
 *     this PMC is currently running on a CPU somewhere.  The thread
 *     doing the PMCRELEASE operation waits by repeatedly doing a
 *     pause() till the runcount comes to zero.
 *
 * The contents of a PMC descriptor (struct pmc) are protected using
 * a spin-mutex.  In order to save space, we use a mutex pool.
 *
 * In terms of lock types used by witness(4), we use:
 * - Type "pmc-sx", used by the global SX lock.
 * - Type "pmc-sleep", for sleep mutexes used by logger threads.
 * - Type "pmc-per-proc", for protecting PMC owner descriptors.
 * - Type "pmc-leaf", used for all other spin mutexes.
 */

/*
 * save the cpu binding of the current kthread
 */

static void
pmc_save_cpu_binding(struct pmc_binding *pb)
{
        PMCDBG0(CPU,BND,2, "save-cpu");
        thread_lock(curthread);
        pb->pb_bound = sched_is_bound(curthread);
        pb->pb_cpu   = curthread->td_oncpu;
        thread_unlock(curthread);
        PMCDBG1(CPU,BND,2, "save-cpu cpu=%d", pb->pb_cpu);
}

/*
 * restore the cpu binding of the current thread
 */

static void
pmc_restore_cpu_binding(struct pmc_binding *pb)
{
        PMCDBG2(CPU,BND,2, "restore-cpu curcpu=%d restore=%d",
            curthread->td_oncpu, pb->pb_cpu);
        thread_lock(curthread);
        if (pb->pb_bound)
                sched_bind(curthread, pb->pb_cpu);
        else
                sched_unbind(curthread);
        thread_unlock(curthread);
        PMCDBG0(CPU,BND,2, "restore-cpu done");
}

/*
 * move execution over the specified cpu and bind it there.
 */

static void
pmc_select_cpu(int cpu)
{
        KASSERT(cpu >= 0 && cpu < pmc_cpu_max(),
            ("[pmc,%d] bad cpu number %d", __LINE__, cpu));

        /* Never move to an inactive CPU. */
        KASSERT(pmc_cpu_is_active(cpu), ("[pmc,%d] selecting inactive "
            "CPU %d", __LINE__, cpu));

        PMCDBG1(CPU,SEL,2, "select-cpu cpu=%d", cpu);
        thread_lock(curthread);
        sched_bind(curthread, cpu);
        thread_unlock(curthread);

        KASSERT(curthread->td_oncpu == cpu,
            ("[pmc,%d] CPU not bound [cpu=%d, curr=%d]", __LINE__,
                cpu, curthread->td_oncpu));

        PMCDBG1(CPU,SEL,2, "select-cpu cpu=%d ok", cpu);
}

/*
 * Force a context switch.
 *
 * We do this by pause'ing for 1 tick -- invoking mi_switch() is not
 * guaranteed to force a context switch.
 */

static void
pmc_force_context_switch(void)
{

        pause("pmcctx", 1);
}

/*
 * Get the file name for an executable.  This is a simple wrapper
 * around vn_fullpath(9).
 */

static void
pmc_getfilename(struct vnode *v, char **fullpath, char **freepath)
{

        *fullpath = "unknown";
        *freepath = NULL;
        vn_fullpath(curthread, v, fullpath, freepath);
}

/*
 * remove an process owning PMCs
 */

void
pmc_remove_owner(struct pmc_owner *po)
{
        struct pmc *pm, *tmp;

        sx_assert(&pmc_sx, SX_XLOCKED);

        PMCDBG1(OWN,ORM,1, "remove-owner po=%p", po);

        /* Remove descriptor from the owner hash table */
        LIST_REMOVE(po, po_next);

        /* release all owned PMC descriptors */
        LIST_FOREACH_SAFE(pm, &po->po_pmcs, pm_next, tmp) {
                PMCDBG1(OWN,ORM,2, "pmc=%p", pm);
                KASSERT(pm->pm_owner == po,
                    ("[pmc,%d] owner %p != po %p", __LINE__, pm->pm_owner, po));

                pmc_release_pmc_descriptor(pm); /* will unlink from the list */
                pmc_destroy_pmc_descriptor(pm);
        }

        KASSERT(po->po_sscount == 0,
            ("[pmc,%d] SS count not zero", __LINE__));
        KASSERT(LIST_EMPTY(&po->po_pmcs),
            ("[pmc,%d] PMC list not empty", __LINE__));

        /* de-configure the log file if present */
        if (po->po_flags & PMC_PO_OWNS_LOGFILE)
                pmclog_deconfigure_log(po);
}

/*
 * remove an owner process record if all conditions are met.
 */

static void
pmc_maybe_remove_owner(struct pmc_owner *po)
{

        PMCDBG1(OWN,OMR,1, "maybe-remove-owner po=%p", po);

        /*
         * Remove owner record if
         * - this process does not own any PMCs
         * - this process has not allocated a system-wide sampling buffer
         */

        if (LIST_EMPTY(&po->po_pmcs) &&
            ((po->po_flags & PMC_PO_OWNS_LOGFILE) == 0)) {
                pmc_remove_owner(po);
                pmc_destroy_owner_descriptor(po);
        }
}

/*
 * Add an association between a target process and a PMC.
 */

static void
pmc_link_target_process(struct pmc *pm, struct pmc_process *pp)
{
        int ri;
        struct pmc_target *pt;

        sx_assert(&pmc_sx, SX_XLOCKED);

        KASSERT(pm != NULL && pp != NULL,
            ("[pmc,%d] Null pm %p or pp %p", __LINE__, pm, pp));
        KASSERT(PMC_IS_VIRTUAL_MODE(PMC_TO_MODE(pm)),
            ("[pmc,%d] Attaching a non-process-virtual pmc=%p to pid=%d",
                __LINE__, pm, pp->pp_proc->p_pid));
        KASSERT(pp->pp_refcnt >= 0 && pp->pp_refcnt <= ((int) md->pmd_npmc - 1),
            ("[pmc,%d] Illegal reference count %d for process record %p",
                __LINE__, pp->pp_refcnt, (void *) pp));

        ri = PMC_TO_ROWINDEX(pm);

        PMCDBG3(PRC,TLK,1, "link-target pmc=%p ri=%d pmc-process=%p",
            pm, ri, pp);

#ifdef  HWPMC_DEBUG
        LIST_FOREACH(pt, &pm->pm_targets, pt_next)
            if (pt->pt_process == pp)
                    KASSERT(0, ("[pmc,%d] pp %p already in pmc %p targets",
                                __LINE__, pp, pm));
#endif

        pt = malloc(sizeof(struct pmc_target), M_PMC, M_WAITOK|M_ZERO);
        pt->pt_process = pp;

        LIST_INSERT_HEAD(&pm->pm_targets, pt, pt_next);

        atomic_store_rel_ptr((uintptr_t *)&pp->pp_pmcs[ri].pp_pmc,
            (uintptr_t)pm);

        if (pm->pm_owner->po_owner == pp->pp_proc)
                pm->pm_flags |= PMC_F_ATTACHED_TO_OWNER;

        /*
         * Initialize the per-process values at this row index.
         */
        pp->pp_pmcs[ri].pp_pmcval = PMC_TO_MODE(pm) == PMC_MODE_TS ?
            pm->pm_sc.pm_reloadcount : 0;

        pp->pp_refcnt++;

}

/*
 * Removes the association between a target process and a PMC.
 */

static void
pmc_unlink_target_process(struct pmc *pm, struct pmc_process *pp)
{
        int ri;
        struct proc *p;
        struct pmc_target *ptgt;

        sx_assert(&pmc_sx, SX_XLOCKED);

        KASSERT(pm != NULL && pp != NULL,
            ("[pmc,%d] Null pm %p or pp %p", __LINE__, pm, pp));

        KASSERT(pp->pp_refcnt >= 1 && pp->pp_refcnt <= (int) md->pmd_npmc,
            ("[pmc,%d] Illegal ref count %d on process record %p",
                __LINE__, pp->pp_refcnt, (void *) pp));

        ri = PMC_TO_ROWINDEX(pm);

        PMCDBG3(PRC,TUL,1, "unlink-target pmc=%p ri=%d pmc-process=%p",
            pm, ri, pp);

        KASSERT(pp->pp_pmcs[ri].pp_pmc == pm,
            ("[pmc,%d] PMC ri %d mismatch pmc %p pp->[ri] %p", __LINE__,
                ri, pm, pp->pp_pmcs[ri].pp_pmc));

        pp->pp_pmcs[ri].pp_pmc = NULL;
        pp->pp_pmcs[ri].pp_pmcval = (pmc_value_t) 0;

        /* Remove owner-specific flags */
        if (pm->pm_owner->po_owner == pp->pp_proc) {
                pp->pp_flags &= ~PMC_PP_ENABLE_MSR_ACCESS;
                pm->pm_flags &= ~PMC_F_ATTACHED_TO_OWNER;
        }

        pp->pp_refcnt--;

        /* Remove the target process from the PMC structure */
        LIST_FOREACH(ptgt, &pm->pm_targets, pt_next)
                if (ptgt->pt_process == pp)
                        break;

        KASSERT(ptgt != NULL, ("[pmc,%d] process %p (pp: %p) not found "
                    "in pmc %p", __LINE__, pp->pp_proc, pp, pm));

        LIST_REMOVE(ptgt, pt_next);
        free(ptgt, M_PMC);

        /* if the PMC now lacks targets, send the owner a SIGIO */
        if (LIST_EMPTY(&pm->pm_targets)) {
                p = pm->pm_owner->po_owner;
                PROC_LOCK(p);
                kern_psignal(p, SIGIO);
                PROC_UNLOCK(p);

                PMCDBG2(PRC,SIG,2, "signalling proc=%p signal=%d", p,
                    SIGIO);
        }
}

/*
 * Check if PMC 'pm' may be attached to target process 't'.
 */

static int
pmc_can_attach(struct pmc *pm, struct proc *t)
{
        struct proc *o;         /* pmc owner */
        struct ucred *oc, *tc;  /* owner, target credentials */
        int decline_attach, i;

        /*
         * A PMC's owner can always attach that PMC to itself.
         */

        if ((o = pm->pm_owner->po_owner) == t)
                return 0;

        PROC_LOCK(o);
        oc = o->p_ucred;
        crhold(oc);
        PROC_UNLOCK(o);

        PROC_LOCK(t);
        tc = t->p_ucred;
        crhold(tc);
        PROC_UNLOCK(t);

        /*
         * The effective uid of the PMC owner should match at least one
         * of the {effective,real,saved} uids of the target process.
         */

        decline_attach = oc->cr_uid != tc->cr_uid &&
            oc->cr_uid != tc->cr_svuid &&
            oc->cr_uid != tc->cr_ruid;

        /*
         * Every one of the target's group ids, must be in the owner's
         * group list.
         */
        for (i = 0; !decline_attach && i < tc->cr_ngroups; i++)
                decline_attach = !groupmember(tc->cr_groups[i], oc);

        /* check the read and saved gids too */
        if (decline_attach == 0)
                decline_attach = !groupmember(tc->cr_rgid, oc) ||
                    !groupmember(tc->cr_svgid, oc);

        crfree(tc);
        crfree(oc);

        return !decline_attach;
}

/*
 * Attach a process to a PMC.
 */

static int
pmc_attach_one_process(struct proc *p, struct pmc *pm)
{
        int ri;
        char *fullpath, *freepath;
        struct pmc_process      *pp;

        sx_assert(&pmc_sx, SX_XLOCKED);

        PMCDBG5(PRC,ATT,2, "attach-one pm=%p ri=%d proc=%p (%d, %s)", pm,
            PMC_TO_ROWINDEX(pm), p, p->p_pid, p->p_comm);

        /*
         * Locate the process descriptor corresponding to process 'p',
         * allocating space as needed.
         *
         * Verify that rowindex 'pm_rowindex' is free in the process
         * descriptor.
         *
         * If not, allocate space for a descriptor and link the
         * process descriptor and PMC.
         */
        ri = PMC_TO_ROWINDEX(pm);

        if ((pp = pmc_find_process_descriptor(p, PMC_FLAG_ALLOCATE)) == NULL)
                return ENOMEM;

        if (pp->pp_pmcs[ri].pp_pmc == pm) /* already present at slot [ri] */
                return EEXIST;

        if (pp->pp_pmcs[ri].pp_pmc != NULL)
                return EBUSY;

        pmc_link_target_process(pm, pp);

        if (PMC_IS_SAMPLING_MODE(PMC_TO_MODE(pm)) &&
            (pm->pm_flags & PMC_F_ATTACHED_TO_OWNER) == 0)
                pm->pm_flags |= PMC_F_NEEDS_LOGFILE;

        pm->pm_flags |= PMC_F_ATTACH_DONE; /* mark as attached */

        /* issue an attach event to a configured log file */
        if (pm->pm_owner->po_flags & PMC_PO_OWNS_LOGFILE) {
                if (p->p_flag & P_KPROC) {
                        fullpath = kernelname;
                        freepath = NULL;
                } else {
                        pmc_getfilename(p->p_textvp, &fullpath, &freepath);
                        pmclog_process_pmcattach(pm, p->p_pid, fullpath);
                }
                free(freepath, M_TEMP);
                if (PMC_IS_SAMPLING_MODE(PMC_TO_MODE(pm)))
                        pmc_log_process_mappings(pm->pm_owner, p);
        }
        /* mark process as using HWPMCs */
        PROC_LOCK(p);
        p->p_flag |= P_HWPMC;
        PROC_UNLOCK(p);

        return 0;
}

/*
 * Attach a process and optionally its children
 */

static int
pmc_attach_process(struct proc *p, struct pmc *pm)
{
        int error;
        struct proc *top;

        sx_assert(&pmc_sx, SX_XLOCKED);

        PMCDBG5(PRC,ATT,1, "attach pm=%p ri=%d proc=%p (%d, %s)", pm,
            PMC_TO_ROWINDEX(pm), p, p->p_pid, p->p_comm);


        /*
         * If this PMC successfully allowed a GETMSR operation
         * in the past, disallow further ATTACHes.
         */

        if ((pm->pm_flags & PMC_PP_ENABLE_MSR_ACCESS) != 0)
                return EPERM;

        if ((pm->pm_flags & PMC_F_DESCENDANTS) == 0)
                return pmc_attach_one_process(p, pm);

        /*
         * Traverse all child processes, attaching them to
         * this PMC.
         */

        sx_slock(&proctree_lock);

        top = p;

        for (;;) {
                if ((error = pmc_attach_one_process(p, pm)) != 0)
                        break;
                if (!LIST_EMPTY(&p->p_children))
                        p = LIST_FIRST(&p->p_children);
                else for (;;) {
                        if (p == top)
                                goto done;
                        if (LIST_NEXT(p, p_sibling)) {
                                p = LIST_NEXT(p, p_sibling);
                                break;
                        }
                        p = p->p_pptr;
                }
        }

        if (error)
                (void) pmc_detach_process(top, pm);

 done:
        sx_sunlock(&proctree_lock);
        return error;
}

/*
 * Detach a process from a PMC.  If there are no other PMCs tracking
 * this process, remove the process structure from its hash table.  If
 * 'flags' contains PMC_FLAG_REMOVE, then free the process structure.
 */

static int
pmc_detach_one_process(struct proc *p, struct pmc *pm, int flags)
{
        int ri;
        struct pmc_process *pp;

        sx_assert(&pmc_sx, SX_XLOCKED);

        KASSERT(pm != NULL,
            ("[pmc,%d] null pm pointer", __LINE__));

        ri = PMC_TO_ROWINDEX(pm);

        PMCDBG6(PRC,ATT,2, "detach-one pm=%p ri=%d proc=%p (%d, %s) flags=0x%x",
            pm, ri, p, p->p_pid, p->p_comm, flags);

        if ((pp = pmc_find_process_descriptor(p, 0)) == NULL)
                return ESRCH;

        if (pp->pp_pmcs[ri].pp_pmc != pm)
                return EINVAL;

        pmc_unlink_target_process(pm, pp);

        /* Issue a detach entry if a log file is configured */
        if (pm->pm_owner->po_flags & PMC_PO_OWNS_LOGFILE)
                pmclog_process_pmcdetach(pm, p->p_pid);

        /*
         * If there are no PMCs targeting this process, we remove its
         * descriptor from the target hash table and unset the P_HWPMC
         * flag in the struct proc.
         */
        KASSERT(pp->pp_refcnt >= 0 && pp->pp_refcnt <= (int) md->pmd_npmc,
            ("[pmc,%d] Illegal refcnt %d for process struct %p",
                __LINE__, pp->pp_refcnt, pp));

        if (pp->pp_refcnt != 0) /* still a target of some PMC */
                return 0;

        pmc_remove_process_descriptor(pp);

        if (flags & PMC_FLAG_REMOVE)
                free(pp, M_PMC);

        PROC_LOCK(p);
        p->p_flag &= ~P_HWPMC;
        PROC_UNLOCK(p);

        return 0;
}

/*
 * Detach a process and optionally its descendants from a PMC.
 */

static int
pmc_detach_process(struct proc *p, struct pmc *pm)
{
        struct proc *top;

        sx_assert(&pmc_sx, SX_XLOCKED);

        PMCDBG5(PRC,ATT,1, "detach pm=%p ri=%d proc=%p (%d, %s)", pm,
            PMC_TO_ROWINDEX(pm), p, p->p_pid, p->p_comm);

        if ((pm->pm_flags & PMC_F_DESCENDANTS) == 0)
                return pmc_detach_one_process(p, pm, PMC_FLAG_REMOVE);

        /*
         * Traverse all children, detaching them from this PMC.  We
         * ignore errors since we could be detaching a PMC from a
         * partially attached proc tree.
         */

        sx_slock(&proctree_lock);

        top = p;

        for (;;) {
                (void) pmc_detach_one_process(p, pm, PMC_FLAG_REMOVE);

                if (!LIST_EMPTY(&p->p_children))
                        p = LIST_FIRST(&p->p_children);
                else for (;;) {
                        if (p == top)
                                goto done;
                        if (LIST_NEXT(p, p_sibling)) {
                                p = LIST_NEXT(p, p_sibling);
                                break;
                        }
                        p = p->p_pptr;
                }
        }

 done:
        sx_sunlock(&proctree_lock);

        if (LIST_EMPTY(&pm->pm_targets))
                pm->pm_flags &= ~PMC_F_ATTACH_DONE;

        return 0;
}


/*
 * Thread context switch IN
 */

static void
pmc_process_csw_in(struct thread *td)
{
        int cpu;
        unsigned int adjri, ri;
        struct pmc *pm;
        struct proc *p;
        struct pmc_cpu *pc;
        struct pmc_hw *phw;
        pmc_value_t newvalue;
        struct pmc_process *pp;
        struct pmc_classdep *pcd;

        p = td->td_proc;

        if ((pp = pmc_find_process_descriptor(p, PMC_FLAG_NONE)) == NULL)
                return;

        KASSERT(pp->pp_proc == td->td_proc,
            ("[pmc,%d] not my thread state", __LINE__));

        critical_enter(); /* no preemption from this point */

        cpu = PCPU_GET(cpuid); /* td->td_oncpu is invalid */

        PMCDBG5(CSW,SWI,1, "cpu=%d proc=%p (%d, %s) pp=%p", cpu, p,
            p->p_pid, p->p_comm, pp);

        KASSERT(cpu >= 0 && cpu < pmc_cpu_max(),
            ("[pmc,%d] weird CPU id %d", __LINE__, cpu));

        pc = pmc_pcpu[cpu];

        for (ri = 0; ri < md->pmd_npmc; ri++) {

                if ((pm = pp->pp_pmcs[ri].pp_pmc) == NULL)
                        continue;

                KASSERT(PMC_IS_VIRTUAL_MODE(PMC_TO_MODE(pm)),
                    ("[pmc,%d] Target PMC in non-virtual mode (%d)",
                        __LINE__, PMC_TO_MODE(pm)));

                KASSERT(PMC_TO_ROWINDEX(pm) == ri,
                    ("[pmc,%d] Row index mismatch pmc %d != ri %d",
                        __LINE__, PMC_TO_ROWINDEX(pm), ri));

                /*
                 * Only PMCs that are marked as 'RUNNING' need
                 * be placed on hardware.
                 */

                if (pm->pm_state != PMC_STATE_RUNNING)
                        continue;

                /* increment PMC runcount */
                atomic_add_rel_int(&pm->pm_runcount, 1);

                /* configure the HWPMC we are going to use. */
                pcd = pmc_ri_to_classdep(md, ri, &adjri);
                pcd->pcd_config_pmc(cpu, adjri, pm);

                phw = pc->pc_hwpmcs[ri];

                KASSERT(phw != NULL,
                    ("[pmc,%d] null hw pointer", __LINE__));

                KASSERT(phw->phw_pmc == pm,
                    ("[pmc,%d] hw->pmc %p != pmc %p", __LINE__,
                        phw->phw_pmc, pm));

                /*
                 * Write out saved value and start the PMC.
                 *
                 * Sampling PMCs use a per-process value, while
                 * counting mode PMCs use a per-pmc value that is
                 * inherited across descendants.
                 */
                if (PMC_TO_MODE(pm) == PMC_MODE_TS) {
                        mtx_pool_lock_spin(pmc_mtxpool, pm);

                        /*
                         * Use the saved value calculated after the most recent
                         * thread switch out to start this counter.  Reset
                         * the saved count in case another thread from this
                         * process switches in before any threads switch out.
                         */
                        newvalue = PMC_PCPU_SAVED(cpu,ri) =
                            pp->pp_pmcs[ri].pp_pmcval;
                        pp->pp_pmcs[ri].pp_pmcval = pm->pm_sc.pm_reloadcount;
                        mtx_pool_unlock_spin(pmc_mtxpool, pm);
                } else {
                        KASSERT(PMC_TO_MODE(pm) == PMC_MODE_TC,
                            ("[pmc,%d] illegal mode=%d", __LINE__,
                            PMC_TO_MODE(pm)));
                        mtx_pool_lock_spin(pmc_mtxpool, pm);
                        newvalue = PMC_PCPU_SAVED(cpu, ri) =
                            pm->pm_gv.pm_savedvalue;
                        mtx_pool_unlock_spin(pmc_mtxpool, pm);
                }

                PMCDBG3(CSW,SWI,1,"cpu=%d ri=%d new=%jd", cpu, ri, newvalue);

                pcd->pcd_write_pmc(cpu, adjri, newvalue);

                /* If a sampling mode PMC, reset stalled state. */
                if (PMC_TO_MODE(pm) == PMC_MODE_TS)
                        CPU_CLR_ATOMIC(cpu, &pm->pm_stalled);

                /* Indicate that we desire this to run. */
                CPU_SET_ATOMIC(cpu, &pm->pm_cpustate);

                /* Start the PMC. */
                pcd->pcd_start_pmc(cpu, adjri);
        }

        /*
         * perform any other architecture/cpu dependent thread
         * switch-in actions.
         */

        (void) (*md->pmd_switch_in)(pc, pp);

        critical_exit();

}

/*
 * Thread context switch OUT.
 */

static void
pmc_process_csw_out(struct thread *td)
{
        int cpu;
        int64_t tmp;
        struct pmc *pm;
        struct proc *p;
        enum pmc_mode mode;
        struct pmc_cpu *pc;
        pmc_value_t newvalue;
        unsigned int adjri, ri;
        struct pmc_process *pp;
        struct pmc_classdep *pcd;


        /*
         * Locate our process descriptor; this may be NULL if
         * this process is exiting and we have already removed
         * the process from the target process table.
         *
         * Note that due to kernel preemption, multiple
         * context switches may happen while the process is
         * exiting.
         *
         * Note also that if the target process cannot be
         * found we still need to deconfigure any PMCs that
         * are currently running on hardware.
         */

        p = td->td_proc;
        pp = pmc_find_process_descriptor(p, PMC_FLAG_NONE);

        /*
         * save PMCs
         */

        critical_enter();

        cpu = PCPU_GET(cpuid); /* td->td_oncpu is invalid */

        PMCDBG5(CSW,SWO,1, "cpu=%d proc=%p (%d, %s) pp=%p", cpu, p,
            p->p_pid, p->p_comm, pp);

        KASSERT(cpu >= 0 && cpu < pmc_cpu_max(),
            ("[pmc,%d weird CPU id %d", __LINE__, cpu));

        pc = pmc_pcpu[cpu];

        /*
         * When a PMC gets unlinked from a target PMC, it will
         * be removed from the target's pp_pmc[] array.
         *
         * However, on a MP system, the target could have been
         * executing on another CPU at the time of the unlink.
         * So, at context switch OUT time, we need to look at
         * the hardware to determine if a PMC is scheduled on
         * it.
         */

        for (ri = 0; ri < md->pmd_npmc; ri++) {

                pcd = pmc_ri_to_classdep(md, ri, &adjri);
                pm  = NULL;
                (void) (*pcd->pcd_get_config)(cpu, adjri, &pm);

                if (pm == NULL) /* nothing at this row index */
                        continue;

                mode = PMC_TO_MODE(pm);
                if (!PMC_IS_VIRTUAL_MODE(mode))
                        continue; /* not a process virtual PMC */

                KASSERT(PMC_TO_ROWINDEX(pm) == ri,
                    ("[pmc,%d] ri mismatch pmc(%d) ri(%d)",
                        __LINE__, PMC_TO_ROWINDEX(pm), ri));

                /*
                 * Change desired state, and then stop if not stalled.
                 * This two-step dance should avoid race conditions where
                 * an interrupt re-enables the PMC after this code has
                 * already checked the pm_stalled flag.
                 */
                CPU_CLR_ATOMIC(cpu, &pm->pm_cpustate);
                if (!CPU_ISSET(cpu, &pm->pm_stalled))
                        pcd->pcd_stop_pmc(cpu, adjri);

                /* reduce this PMC's runcount */
                atomic_subtract_rel_int(&pm->pm_runcount, 1);

                /*
                 * If this PMC is associated with this process,
                 * save the reading.
                 */

                if (pm->pm_state != PMC_STATE_DELETED && pp != NULL &&
                    pp->pp_pmcs[ri].pp_pmc != NULL) {
                        KASSERT(pm == pp->pp_pmcs[ri].pp_pmc,
                            ("[pmc,%d] pm %p != pp_pmcs[%d] %p", __LINE__,
                                pm, ri, pp->pp_pmcs[ri].pp_pmc));

                        KASSERT(pp->pp_refcnt > 0,
                            ("[pmc,%d] pp refcnt = %d", __LINE__,
                                pp->pp_refcnt));

                        pcd->pcd_read_pmc(cpu, adjri, &newvalue);

                        if (mode == PMC_MODE_TS) {
                                PMCDBG3(CSW,SWO,1,"cpu=%d ri=%d tmp=%jd (samp)",
                                    cpu, ri, PMC_PCPU_SAVED(cpu,ri) - newvalue);

                                /*
                                 * For sampling process-virtual PMCs,
                                 * newvalue is the number of events to be seen
                                 * until the next sampling interrupt.
                                 * We can just add the events left from this
                                 * invocation to the counter, then adjust
                                 * in case we overflow our range.
                                 *
                                 * (Recall that we reload the counter every
                                 * time we use it.)
                                 */
                                mtx_pool_lock_spin(pmc_mtxpool, pm);

                                pp->pp_pmcs[ri].pp_pmcval += newvalue;
                                if (pp->pp_pmcs[ri].pp_pmcval >
                                    pm->pm_sc.pm_reloadcount)
                                        pp->pp_pmcs[ri].pp_pmcval -=
                                            pm->pm_sc.pm_reloadcount;
                                KASSERT(pp->pp_pmcs[ri].pp_pmcval > 0 &&
                                    pp->pp_pmcs[ri].pp_pmcval <=
                                    pm->pm_sc.pm_reloadcount,
                                    ("[pmc,%d] pp_pmcval outside of expected "
                                    "range cpu=%d ri=%d pp_pmcval=%jx "
                                    "pm_reloadcount=%jx", __LINE__, cpu, ri,
                                    pp->pp_pmcs[ri].pp_pmcval,
                                    pm->pm_sc.pm_reloadcount));
                                mtx_pool_unlock_spin(pmc_mtxpool, pm);

                        } else {
                                tmp = newvalue - PMC_PCPU_SAVED(cpu,ri);

                                PMCDBG3(CSW,SWO,1,"cpu=%d ri=%d tmp=%jd (count)",
                                    cpu, ri, tmp);

                                /*
                                 * For counting process-virtual PMCs,
                                 * we expect the count to be
                                 * increasing monotonically, modulo a 64
                                 * bit wraparound.
                                 */
                                KASSERT(tmp >= 0,
                                    ("[pmc,%d] negative increment cpu=%d "
                                     "ri=%d newvalue=%jx saved=%jx "
                                     "incr=%jx", __LINE__, cpu, ri,
                                     newvalue, PMC_PCPU_SAVED(cpu,ri), tmp));

                                mtx_pool_lock_spin(pmc_mtxpool, pm);
                                pm->pm_gv.pm_savedvalue += tmp;
                                pp->pp_pmcs[ri].pp_pmcval += tmp;
                                mtx_pool_unlock_spin(pmc_mtxpool, pm);

                                if (pm->pm_flags & PMC_F_LOG_PROCCSW)
                                        pmclog_process_proccsw(pm, pp, tmp);
                        }
                }

                /* mark hardware as free */
                pcd->pcd_config_pmc(cpu, adjri, NULL);
        }

        /*
         * perform any other architecture/cpu dependent thread
         * switch out functions.
         */

        (void) (*md->pmd_switch_out)(pc, pp);

        critical_exit();
}

/*
 * A mapping change for a process.
 */

static void
pmc_process_mmap(struct thread *td, struct pmckern_map_in *pkm)
{
        int ri;
        pid_t pid;
        char *fullpath, *freepath;
        const struct pmc *pm;
        struct pmc_owner *po;
        const struct pmc_process *pp;

        freepath = fullpath = NULL;
        pmc_getfilename((struct vnode *) pkm->pm_file, &fullpath, &freepath);

        pid = td->td_proc->p_pid;

        /* Inform owners of all system-wide sampling PMCs. */
        LIST_FOREACH(po, &pmc_ss_owners, po_ssnext)
            if (po->po_flags & PMC_PO_OWNS_LOGFILE)
                pmclog_process_map_in(po, pid, pkm->pm_address, fullpath);

        if ((pp = pmc_find_process_descriptor(td->td_proc, 0)) == NULL)
                goto done;

        /*
         * Inform sampling PMC owners tracking this process.
         */
        for (ri = 0; ri < md->pmd_npmc; ri++)
                if ((pm = pp->pp_pmcs[ri].pp_pmc) != NULL &&
                    PMC_IS_SAMPLING_MODE(PMC_TO_MODE(pm)))
                        pmclog_process_map_in(pm->pm_owner,
                            pid, pkm->pm_address, fullpath);

  done:
        if (freepath)
                free(freepath, M_TEMP);
}


/*
 * Log an munmap request.
 */

static void
pmc_process_munmap(struct thread *td, struct pmckern_map_out *pkm)
{
        int ri;
        pid_t pid;
        struct pmc_owner *po;
        const struct pmc *pm;
        const struct pmc_process *pp;

        pid = td->td_proc->p_pid;

        LIST_FOREACH(po, &pmc_ss_owners, po_ssnext)
            if (po->po_flags & PMC_PO_OWNS_LOGFILE)
                pmclog_process_map_out(po, pid, pkm->pm_address,
                    pkm->pm_address + pkm->pm_size);

        if ((pp = pmc_find_process_descriptor(td->td_proc, 0)) == NULL)
                return;

        for (ri = 0; ri < md->pmd_npmc; ri++)
                if ((pm = pp->pp_pmcs[ri].pp_pmc) != NULL &&
                    PMC_IS_SAMPLING_MODE(PMC_TO_MODE(pm)))
                        pmclog_process_map_out(pm->pm_owner, pid,
                            pkm->pm_address, pkm->pm_address + pkm->pm_size);
}

/*
 * Log mapping information about the kernel.
 */

static void
pmc_log_kernel_mappings(struct pmc *pm)
{
        struct pmc_owner *po;
        struct pmckern_map_in *km, *kmbase;

        sx_assert(&pmc_sx, SX_LOCKED);
        KASSERT(PMC_IS_SAMPLING_MODE(PMC_TO_MODE(pm)),
            ("[pmc,%d] non-sampling PMC (%p) desires mapping information",
                __LINE__, (void *) pm));

        po = pm->pm_owner;

        if (po->po_flags & PMC_PO_INITIAL_MAPPINGS_DONE)
                return;

        /*
         * Log the current set of kernel modules.
         */
        kmbase = linker_hwpmc_list_objects();
        for (km = kmbase; km->pm_file != NULL; km++) {
                PMCDBG2(LOG,REG,1,"%s %p", (char *) km->pm_file,
                    (void *) km->pm_address);
                pmclog_process_map_in(po, (pid_t) -1, km->pm_address,
                    km->pm_file);
        }
        free(kmbase, M_LINKER);

        po->po_flags |= PMC_PO_INITIAL_MAPPINGS_DONE;
}

/*
 * Log the mappings for a single process.
 */

static void
pmc_log_process_mappings(struct pmc_owner *po, struct proc *p)
{
        vm_map_t map;
        struct vnode *vp;
        struct vmspace *vm;
        vm_map_entry_t entry;
        vm_offset_t last_end;
        u_int last_timestamp;
        struct vnode *last_vp;
        vm_offset_t start_addr;
        vm_object_t obj, lobj, tobj;
        char *fullpath, *freepath;

        last_vp = NULL;
        last_end = (vm_offset_t) 0;
        fullpath = freepath = NULL;

        if ((vm = vmspace_acquire_ref(p)) == NULL)
                return;

        map = &vm->vm_map;
        vm_map_lock_read(map);

        for (entry = map->header.next; entry != &map->header; entry = entry->next) {

                if (entry == NULL) {
                        PMCDBG2(LOG,OPS,2, "hwpmc: vm_map entry unexpectedly "
                            "NULL! pid=%d vm_map=%p\n", p->p_pid, map);
                        break;
                }

                /*
                 * We only care about executable map entries.
                 */
                if ((entry->eflags & MAP_ENTRY_IS_SUB_MAP) ||
                    !(entry->protection & VM_PROT_EXECUTE) ||
                    (entry->object.vm_object == NULL)) {
                        continue;
                }

                obj = entry->object.vm_object;
                VM_OBJECT_RLOCK(obj);

                /* 
                 * Walk the backing_object list to find the base
                 * (non-shadowed) vm_object.
                 */
                for (lobj = tobj = obj; tobj != NULL; tobj = tobj->backing_object) {
                        if (tobj != obj)
                                VM_OBJECT_RLOCK(tobj);
                        if (lobj != obj)
                                VM_OBJECT_RUNLOCK(lobj);
                        lobj = tobj;
                }

                /*
                 * At this point lobj is the base vm_object and it is locked.
                 */
                if (lobj == NULL) {
                        PMCDBG3(LOG,OPS,2, "hwpmc: lobj unexpectedly NULL! pid=%d "
                            "vm_map=%p vm_obj=%p\n", p->p_pid, map, obj);
                        VM_OBJECT_RUNLOCK(obj);
                        continue;
                }

                vp = vm_object_vnode(lobj);
                if (vp == NULL) {
                        if (lobj != obj)
                                VM_OBJECT_RUNLOCK(lobj);
                        VM_OBJECT_RUNLOCK(obj);
                        continue;
                }

                /*
                 * Skip contiguous regions that point to the same
                 * vnode, so we don't emit redundant MAP-IN
                 * directives.
                 */
                if (entry->start == last_end && vp == last_vp) {
                        last_end = entry->end;
                        if (lobj != obj)
                                VM_OBJECT_RUNLOCK(lobj);
                        VM_OBJECT_RUNLOCK(obj);
                        continue;
                }

                /* 
                 * We don't want to keep the proc's vm_map or this
                 * vm_object locked while we walk the pathname, since
                 * vn_fullpath() can sleep.  However, if we drop the
                 * lock, it's possible for concurrent activity to
                 * modify the vm_map list.  To protect against this,
                 * we save the vm_map timestamp before we release the
                 * lock, and check it after we reacquire the lock
                 * below.
                 */
                start_addr = entry->start;
                last_end = entry->end;
                last_timestamp = map->timestamp;
                vm_map_unlock_read(map);

                vref(vp);
                if (lobj != obj)
                        VM_OBJECT_RUNLOCK(lobj);

                VM_OBJECT_RUNLOCK(obj);

                freepath = NULL;
                pmc_getfilename(vp, &fullpath, &freepath);
                last_vp = vp;

                vrele(vp);

                vp = NULL;
                pmclog_process_map_in(po, p->p_pid, start_addr, fullpath);
                if (freepath)
                        free(freepath, M_TEMP);

                vm_map_lock_read(map);

                /*
                 * If our saved timestamp doesn't match, this means
                 * that the vm_map was modified out from under us and
                 * we can't trust our current "entry" pointer.  Do a
                 * new lookup for this entry.  If there is no entry
                 * for this address range, vm_map_lookup_entry() will
                 * return the previous one, so we always want to go to
                 * entry->next on the next loop iteration.
                 * 
                 * There is an edge condition here that can occur if
                 * there is no entry at or before this address.  In
                 * this situation, vm_map_lookup_entry returns
                 * &map->header, which would cause our loop to abort
                 * without processing the rest of the map.  However,
                 * in practice this will never happen for process
                 * vm_map.  This is because the executable's text
                 * segment is the first mapping in the proc's address
                 * space, and this mapping is never removed until the
                 * process exits, so there will always be a non-header
                 * entry at or before the requested address for
                 * vm_map_lookup_entry to return.
                 */
                if (map->timestamp != last_timestamp)
                        vm_map_lookup_entry(map, last_end - 1, &entry);
        }

        vm_map_unlock_read(map);
        vmspace_free(vm);
        return;
}

/*
 * Log mappings for all processes in the system.
 */

static void
pmc_log_all_process_mappings(struct pmc_owner *po)
{
        struct proc *p, *top;

        sx_assert(&pmc_sx, SX_XLOCKED);

        if ((p = pfind(1)) == NULL)
                panic("[pmc,%d] Cannot find init", __LINE__);

        PROC_UNLOCK(p);

        sx_slock(&proctree_lock);

        top = p;

        for (;;) {
                pmc_log_process_mappings(po, p);
                if (!LIST_EMPTY(&p->p_children))
                        p = LIST_FIRST(&p->p_children);
                else for (;;) {
                        if (p == top)
                                goto done;
                        if (LIST_NEXT(p, p_sibling)) {
                                p = LIST_NEXT(p, p_sibling);
                                break;
                        }
                        p = p->p_pptr;
                }
        }
 done:
        sx_sunlock(&proctree_lock);
}

/*
 * The 'hook' invoked from the kernel proper
 */


#ifdef  HWPMC_DEBUG
const char *pmc_hooknames[] = {
        /* these strings correspond to PMC_FN_* in <sys/pmckern.h> */
        "",
        "EXEC",
        "CSW-IN",
        "CSW-OUT",
        "SAMPLE",
        "UNUSED1",
        "UNUSED2",
        "MMAP",
        "MUNMAP",
        "CALLCHAIN-NMI",
        "CALLCHAIN-SOFT",
        "SOFTSAMPLING"
};
#endif

static int
pmc_hook_handler(struct thread *td, int function, void *arg)
{

        PMCDBG4(MOD,PMH,1, "hook td=%p func=%d \"%s\" arg=%p", td, function,
            pmc_hooknames[function], arg);

        switch (function)
        {

        /*
         * Process exec()
         */

        case PMC_FN_PROCESS_EXEC:
        {
                char *fullpath, *freepath;
                unsigned int ri;
                int is_using_hwpmcs;
                struct pmc *pm;
                struct proc *p;
                struct pmc_owner *po;
                struct pmc_process *pp;
                struct pmckern_procexec *pk;

                sx_assert(&pmc_sx, SX_XLOCKED);

                p = td->td_proc;
                pmc_getfilename(p->p_textvp, &fullpath, &freepath);

                pk = (struct pmckern_procexec *) arg;

                /* Inform owners of SS mode PMCs of the exec event. */
                LIST_FOREACH(po, &pmc_ss_owners, po_ssnext)
                    if (po->po_flags & PMC_PO_OWNS_LOGFILE)
                            pmclog_process_procexec(po, PMC_ID_INVALID,
                                p->p_pid, pk->pm_entryaddr, fullpath);

                PROC_LOCK(p);
                is_using_hwpmcs = p->p_flag & P_HWPMC;
                PROC_UNLOCK(p);

                if (!is_using_hwpmcs) {
                        if (freepath)
                                free(freepath, M_TEMP);
                        break;
                }

                /*
                 * PMCs are not inherited across an exec():  remove any
                 * PMCs that this process is the owner of.
                 */

                if ((po = pmc_find_owner_descriptor(p)) != NULL) {
                        pmc_remove_owner(po);
                        pmc_destroy_owner_descriptor(po);
                }

                /*
                 * If the process being exec'ed is not the target of any
                 * PMC, we are done.
                 */
                if ((pp = pmc_find_process_descriptor(p, 0)) == NULL) {
                        if (freepath)
                                free(freepath, M_TEMP);
                        break;
                }

                /*
                 * Log the exec event to all monitoring owners.  Skip
                 * owners who have already received the event because
                 * they had system sampling PMCs active.
                 */
                for (ri = 0; ri < md->pmd_npmc; ri++)
                        if ((pm = pp->pp_pmcs[ri].pp_pmc) != NULL) {
                                po = pm->pm_owner;
                                if (po->po_sscount == 0 &&
                                    po->po_flags & PMC_PO_OWNS_LOGFILE)
                                        pmclog_process_procexec(po, pm->pm_id,
                                            p->p_pid, pk->pm_entryaddr,
                                            fullpath);
                        }

                if (freepath)
                        free(freepath, M_TEMP);


                PMCDBG4(PRC,EXC,1, "exec proc=%p (%d, %s) cred-changed=%d",
                    p, p->p_pid, p->p_comm, pk->pm_credentialschanged);

                if (pk->pm_credentialschanged == 0) /* no change */
                        break;

                /*
                 * If the newly exec()'ed process has a different credential
                 * than before, allow it to be the target of a PMC only if
                 * the PMC's owner has sufficient privilege.
                 */

                for (ri = 0; ri < md->pmd_npmc; ri++)
                        if ((pm = pp->pp_pmcs[ri].pp_pmc) != NULL)
                                if (pmc_can_attach(pm, td->td_proc) != 0)
                                        pmc_detach_one_process(td->td_proc,
                                            pm, PMC_FLAG_NONE);

                KASSERT(pp->pp_refcnt >= 0 && pp->pp_refcnt <= (int) md->pmd_npmc,
                    ("[pmc,%d] Illegal ref count %d on pp %p", __LINE__,
                        pp->pp_refcnt, pp));

                /*
                 * If this process is no longer the target of any
                 * PMCs, we can remove the process entry and free
                 * up space.
                 */

                if (pp->pp_refcnt == 0) {
                        pmc_remove_process_descriptor(pp);
                        free(pp, M_PMC);
                        break;
                }

        }
        break;

        case PMC_FN_CSW_IN:
                pmc_process_csw_in(td);
                break;

        case PMC_FN_CSW_OUT:
                pmc_process_csw_out(td);
                break;

        /*
         * Process accumulated PC samples.
         *
         * This function is expected to be called by hardclock() for
         * each CPU that has accumulated PC samples.
         *
         * This function is to be executed on the CPU whose samples
         * are being processed.
         */
        case PMC_FN_DO_SAMPLES:

                /*
                 * Clear the cpu specific bit in the CPU mask before
                 * do the rest of the processing.  If the NMI handler
                 * gets invoked after the "atomic_clear_int()" call
                 * below but before "pmc_process_samples()" gets
                 * around to processing the interrupt, then we will
                 * come back here at the next hardclock() tick (and
                 * may find nothing to do if "pmc_process_samples()"
                 * had already processed the interrupt).  We don't
                 * lose the interrupt sample.
                 */
                CPU_CLR_ATOMIC(PCPU_GET(cpuid), &pmc_cpumask);
                pmc_process_samples(PCPU_GET(cpuid), PMC_HR);
                pmc_process_samples(PCPU_GET(cpuid), PMC_SR);
                break;

        case PMC_FN_MMAP:
                sx_assert(&pmc_sx, SX_LOCKED);
                pmc_process_mmap(td, (struct pmckern_map_in *) arg);
                break;

        case PMC_FN_MUNMAP:
                sx_assert(&pmc_sx, SX_LOCKED);
                pmc_process_munmap(td, (struct pmckern_map_out *) arg);
                break;

        case PMC_FN_USER_CALLCHAIN:
                /*
                 * Record a call chain.
                 */
                KASSERT(td == curthread, ("[pmc,%d] td != curthread",
                    __LINE__));

                pmc_capture_user_callchain(PCPU_GET(cpuid), PMC_HR,
                    (struct trapframe *) arg);
                td->td_pflags &= ~TDP_CALLCHAIN;
                break;

        case PMC_FN_USER_CALLCHAIN_SOFT:
                /*
                 * Record a call chain.
                 */
                KASSERT(td == curthread, ("[pmc,%d] td != curthread",
                    __LINE__));
                pmc_capture_user_callchain(PCPU_GET(cpuid), PMC_SR,
                    (struct trapframe *) arg);
                td->td_pflags &= ~TDP_CALLCHAIN;
                break;

        case PMC_FN_SOFT_SAMPLING:
                /*
                 * Call soft PMC sampling intr.
                 */
                pmc_soft_intr((struct pmckern_soft *) arg);
                break;

        default:
#ifdef  HWPMC_DEBUG
                KASSERT(0, ("[pmc,%d] unknown hook %d\n", __LINE__, function));
#endif
                break;

        }

        return 0;
}

/*
 * allocate a 'struct pmc_owner' descriptor in the owner hash table.
 */

static struct pmc_owner *
pmc_allocate_owner_descriptor(struct proc *p)
{
        uint32_t hindex;
        struct pmc_owner *po;
        struct pmc_ownerhash *poh;

        hindex = PMC_HASH_PTR(p, pmc_ownerhashmask);
        poh = &pmc_ownerhash[hindex];

        /* allocate space for N pointers and one descriptor struct */
        po = malloc(sizeof(struct pmc_owner), M_PMC, M_WAITOK|M_ZERO);
        po->po_owner = p;
        LIST_INSERT_HEAD(poh, po, po_next); /* insert into hash table */

        TAILQ_INIT(&po->po_logbuffers);
        mtx_init(&po->po_mtx, "pmc-owner-mtx", "pmc-per-proc", MTX_SPIN);

        PMCDBG4(OWN,ALL,1, "allocate-owner proc=%p (%d, %s) pmc-owner=%p",
            p, p->p_pid, p->p_comm, po);

        return po;
}

static void
pmc_destroy_owner_descriptor(struct pmc_owner *po)
{

        PMCDBG4(OWN,REL,1, "destroy-owner po=%p proc=%p (%d, %s)",
            po, po->po_owner, po->po_owner->p_pid, po->po_owner->p_comm);

        mtx_destroy(&po->po_mtx);
        free(po, M_PMC);
}

/*
 * find the descriptor corresponding to process 'p', adding or removing it
 * as specified by 'mode'.
 */

static struct pmc_process *
pmc_find_process_descriptor(struct proc *p, uint32_t mode)
{
        uint32_t hindex;
        struct pmc_process *pp, *ppnew;
        struct pmc_processhash *pph;

        hindex = PMC_HASH_PTR(p, pmc_processhashmask);
        pph = &pmc_processhash[hindex];

        ppnew = NULL;

        /*
         * Pre-allocate memory in the FIND_ALLOCATE case since we
         * cannot call malloc(9) once we hold a spin lock.
         */
        if (mode & PMC_FLAG_ALLOCATE)
                ppnew = malloc(sizeof(struct pmc_process) + md->pmd_npmc *
                    sizeof(struct pmc_targetstate), M_PMC, M_WAITOK|M_ZERO);

        mtx_lock_spin(&pmc_processhash_mtx);
        LIST_FOREACH(pp, pph, pp_next)
            if (pp->pp_proc == p)
                    break;

        if ((mode & PMC_FLAG_REMOVE) && pp != NULL)
                LIST_REMOVE(pp, pp_next);

        if ((mode & PMC_FLAG_ALLOCATE) && pp == NULL &&
            ppnew != NULL) {
                ppnew->pp_proc = p;
                LIST_INSERT_HEAD(pph, ppnew, pp_next);
                pp = ppnew;
                ppnew = NULL;
        }
        mtx_unlock_spin(&pmc_processhash_mtx);

        if (pp != NULL && ppnew != NULL)
                free(ppnew, M_PMC);

        return pp;
}

/*
 * remove a process descriptor from the process hash table.
 */

static void
pmc_remove_process_descriptor(struct pmc_process *pp)
{
        KASSERT(pp->pp_refcnt == 0,
            ("[pmc,%d] Removing process descriptor %p with count %d",
                __LINE__, pp, pp->pp_refcnt));

        mtx_lock_spin(&pmc_processhash_mtx);
        LIST_REMOVE(pp, pp_next);
        mtx_unlock_spin(&pmc_processhash_mtx);
}


/*
 * find an owner descriptor corresponding to proc 'p'
 */

static struct pmc_owner *
pmc_find_owner_descriptor(struct proc *p)
{
        uint32_t hindex;
        struct pmc_owner *po;
        struct pmc_ownerhash *poh;

        hindex = PMC_HASH_PTR(p, pmc_ownerhashmask);
        poh = &pmc_ownerhash[hindex];

        po = NULL;
        LIST_FOREACH(po, poh, po_next)
            if (po->po_owner == p)
                    break;

        PMCDBG5(OWN,FND,1, "find-owner proc=%p (%d, %s) hindex=0x%x -> "
            "pmc-owner=%p", p, p->p_pid, p->p_comm, hindex, po);

        return po;
}

/*
 * pmc_allocate_pmc_descriptor
 *
 * Allocate a pmc descriptor and initialize its
 * fields.
 */

static struct pmc *
pmc_allocate_pmc_descriptor(void)
{
        struct pmc *pmc;

        pmc = malloc(sizeof(struct pmc), M_PMC, M_WAITOK|M_ZERO);

        PMCDBG1(PMC,ALL,1, "allocate-pmc -> pmc=%p", pmc);

        return pmc;
}

/*
 * Destroy a pmc descriptor.
 */

static void
pmc_destroy_pmc_descriptor(struct pmc *pm)
{

        KASSERT(pm->pm_state == PMC_STATE_DELETED ||
            pm->pm_state == PMC_STATE_FREE,
            ("[pmc,%d] destroying non-deleted PMC", __LINE__));
        KASSERT(LIST_EMPTY(&pm->pm_targets),
            ("[pmc,%d] destroying pmc with targets", __LINE__));
        KASSERT(pm->pm_owner == NULL,
            ("[pmc,%d] destroying pmc attached to an owner", __LINE__));
        KASSERT(pm->pm_runcount == 0,
            ("[pmc,%d] pmc has non-zero run count %d", __LINE__,
                pm->pm_runcount));

        free(pm, M_PMC);
}

static void
pmc_wait_for_pmc_idle(struct pmc *pm)
{
#ifdef HWPMC_DEBUG
        volatile int maxloop;

        maxloop = 100 * pmc_cpu_max();
#endif
        /*
         * Loop (with a forced context switch) till the PMC's runcount
         * comes down to zero.
         */
        while (atomic_load_acq_32(&pm->pm_runcount) > 0) {
#ifdef HWPMC_DEBUG
                maxloop--;
                KASSERT(maxloop > 0,
                    ("[pmc,%d] (ri%d, rc%d) waiting too long for "
                        "pmc to be free", __LINE__,
                        PMC_TO_ROWINDEX(pm), pm->pm_runcount));
#endif
                pmc_force_context_switch();
        }
}

/*
 * This function does the following things:
 *
 *  - detaches the PMC from hardware
 *  - unlinks all target threads that were attached to it
 *  - removes the PMC from its owner's list
 *  - destroys the PMC private mutex
 *
 * Once this function completes, the given pmc pointer can be freed by
 * calling pmc_destroy_pmc_descriptor().
 */

static void
pmc_release_pmc_descriptor(struct pmc *pm)
{
        enum pmc_mode mode;
        struct pmc_hw *phw;
        u_int adjri, ri, cpu;
        struct pmc_owner *po;
        struct pmc_binding pb;
        struct pmc_process *pp;
        struct pmc_classdep *pcd;
        struct pmc_target *ptgt, *tmp;

        sx_assert(&pmc_sx, SX_XLOCKED);

        KASSERT(pm, ("[pmc,%d] null pmc", __LINE__));

        ri   = PMC_TO_ROWINDEX(pm);
        pcd  = pmc_ri_to_classdep(md, ri, &adjri);
        mode = PMC_TO_MODE(pm);

        PMCDBG3(PMC,REL,1, "release-pmc pmc=%p ri=%d mode=%d", pm, ri,
            mode);

        /*
         * First, we take the PMC off hardware.
         */
        cpu = 0;
        if (PMC_IS_SYSTEM_MODE(mode)) {

                /*
                 * A system mode PMC runs on a specific CPU.  Switch
                 * to this CPU and turn hardware off.
                 */
                pmc_save_cpu_binding(&pb);

                cpu = PMC_TO_CPU(pm);

                pmc_select_cpu(cpu);

                /* switch off non-stalled CPUs */
                CPU_CLR_ATOMIC(cpu, &pm->pm_cpustate);
                if (pm->pm_state == PMC_STATE_RUNNING &&
                    !CPU_ISSET(cpu, &pm->pm_stalled)) {

                        phw = pmc_pcpu[cpu]->pc_hwpmcs[ri];

                        KASSERT(phw->phw_pmc == pm,
                            ("[pmc, %d] pmc ptr ri(%d) hw(%p) pm(%p)",
                                __LINE__, ri, phw->phw_pmc, pm));
                        PMCDBG2(PMC,REL,2, "stopping cpu=%d ri=%d", cpu, ri);

                        critical_enter();
                        pcd->pcd_stop_pmc(cpu, adjri);
                        critical_exit();
                }

                PMCDBG2(PMC,REL,2, "decfg cpu=%d ri=%d", cpu, ri);

                critical_enter();
                pcd->pcd_config_pmc(cpu, adjri, NULL);
                critical_exit();

                /* adjust the global and process count of SS mode PMCs */
                if (mode == PMC_MODE_SS && pm->pm_state == PMC_STATE_RUNNING) {
                        po = pm->pm_owner;
                        po->po_sscount--;
                        if (po->po_sscount == 0) {
                                atomic_subtract_rel_int(&pmc_ss_count, 1);
                                LIST_REMOVE(po, po_ssnext);
                        }
                }

                pm->pm_state = PMC_STATE_DELETED;

                pmc_restore_cpu_binding(&pb);

                /*
                 * We could have references to this PMC structure in
                 * the per-cpu sample queues.  Wait for the queue to
                 * drain.
                 */
                pmc_wait_for_pmc_idle(pm);

        } else if (PMC_IS_VIRTUAL_MODE(mode)) {

                /*
                 * A virtual PMC could be running on multiple CPUs at
                 * a given instant.
                 *
                 * By marking its state as DELETED, we ensure that
                 * this PMC is never further scheduled on hardware.
                 *
                 * Then we wait till all CPUs are done with this PMC.
                 */
                pm->pm_state = PMC_STATE_DELETED;


                /* Wait for the PMCs runcount to come to zero. */
                pmc_wait_for_pmc_idle(pm);

                /*
                 * At this point the PMC is off all CPUs and cannot be
                 * freshly scheduled onto a CPU.  It is now safe to
                 * unlink all targets from this PMC.  If a
                 * process-record's refcount falls to zero, we remove
                 * it from the hash table.  The module-wide SX lock
                 * protects us from races.
                 */
                LIST_FOREACH_SAFE(ptgt, &pm->pm_targets, pt_next, tmp) {
                        pp = ptgt->pt_process;
                        pmc_unlink_target_process(pm, pp); /* frees 'ptgt' */

                        PMCDBG1(PMC,REL,3, "pp->refcnt=%d", pp->pp_refcnt);

                        /*
                         * If the target process record shows that no
                         * PMCs are attached to it, reclaim its space.
                         */

                        if (pp->pp_refcnt == 0) {
                                pmc_remove_process_descriptor(pp);
                                free(pp, M_PMC);
                        }
                }

                cpu = curthread->td_oncpu; /* setup cpu for pmd_release() */

        }

        /*
         * Release any MD resources
         */
        (void) pcd->pcd_release_pmc(cpu, adjri, pm);

        /*
         * Update row disposition
         */

        if (PMC_IS_SYSTEM_MODE(PMC_TO_MODE(pm)))
                PMC_UNMARK_ROW_STANDALONE(ri);
        else
                PMC_UNMARK_ROW_THREAD(ri);

        /* unlink from the owner's list */
        if (pm->pm_owner) {
                LIST_REMOVE(pm, pm_next);
                pm->pm_owner = NULL;
        }
}

/*
 * Register an owner and a pmc.
 */

static int
pmc_register_owner(struct proc *p, struct pmc *pmc)
{
        struct pmc_owner *po;

        sx_assert(&pmc_sx, SX_XLOCKED);

        if ((po = pmc_find_owner_descriptor(p)) == NULL)
                if ((po = pmc_allocate_owner_descriptor(p)) == NULL)
                        return ENOMEM;

        KASSERT(pmc->pm_owner == NULL,
            ("[pmc,%d] attempting to own an initialized PMC", __LINE__));
        pmc->pm_owner  = po;

        LIST_INSERT_HEAD(&po->po_pmcs, pmc, pm_next);

        PROC_LOCK(p);
        p->p_flag |= P_HWPMC;
        PROC_UNLOCK(p);

        if (po->po_flags & PMC_PO_OWNS_LOGFILE)
                pmclog_process_pmcallocate(pmc);

        PMCDBG2(PMC,REG,1, "register-owner pmc-owner=%p pmc=%p",
            po, pmc);

        return 0;
}

/*
 * Return the current row disposition:
 * == 0 => FREE
 *  > 0 => PROCESS MODE
 *  < 0 => SYSTEM MODE
 */

int
pmc_getrowdisp(int ri)
{
        return pmc_pmcdisp[ri];
}

/*
 * Check if a PMC at row index 'ri' can be allocated to the current
 * process.
 *
 * Allocation can fail if:
 *   - the current process is already being profiled by a PMC at index 'ri',
 *     attached to it via OP_PMCATTACH.
 *   - the current process has already allocated a PMC at index 'ri'
 *     via OP_ALLOCATE.
 */

static int
pmc_can_allocate_rowindex(struct proc *p, unsigned int ri, int cpu)
{
        enum pmc_mode mode;
        struct pmc *pm;
        struct pmc_owner *po;
        struct pmc_process *pp;

        PMCDBG5(PMC,ALR,1, "can-allocate-rowindex proc=%p (%d, %s) ri=%d "
            "cpu=%d", p, p->p_pid, p->p_comm, ri, cpu);

        /*
         * We shouldn't have already allocated a process-mode PMC at
         * row index 'ri'.
         *
         * We shouldn't have allocated a system-wide PMC on the same
         * CPU and same RI.
         */
        if ((po = pmc_find_owner_descriptor(p)) != NULL)
                LIST_FOREACH(pm, &po->po_pmcs, pm_next) {
                    if (PMC_TO_ROWINDEX(pm) == ri) {
                            mode = PMC_TO_MODE(pm);
                            if (PMC_IS_VIRTUAL_MODE(mode))
                                    return EEXIST;
                            if (PMC_IS_SYSTEM_MODE(mode) &&
                                (int) PMC_TO_CPU(pm) == cpu)
                                    return EEXIST;
                    }
                }

        /*
         * We also shouldn't be the target of any PMC at this index
         * since otherwise a PMC_ATTACH to ourselves will fail.
         */
        if ((pp = pmc_find_process_descriptor(p, 0)) != NULL)
                if (pp->pp_pmcs[ri].pp_pmc)
                        return EEXIST;

        PMCDBG4(PMC,ALR,2, "can-allocate-rowindex proc=%p (%d, %s) ri=%d ok",
            p, p->p_pid, p->p_comm, ri);

        return 0;
}

/*
 * Check if a given PMC at row index 'ri' can be currently used in
 * mode 'mode'.
 */

static int
pmc_can_allocate_row(int ri, enum pmc_mode mode)
{
        enum pmc_disp   disp;

        sx_assert(&pmc_sx, SX_XLOCKED);

        PMCDBG2(PMC,ALR,1, "can-allocate-row ri=%d mode=%d", ri, mode);

        if (PMC_IS_SYSTEM_MODE(mode))
                disp = PMC_DISP_STANDALONE;
        else
                disp = PMC_DISP_THREAD;

        /*
         * check disposition for PMC row 'ri':
         *
         * Expected disposition         Row-disposition         Result
         *
         * STANDALONE                   STANDALONE or FREE      proceed
         * STANDALONE                   THREAD                  fail
         * THREAD                       THREAD or FREE          proceed
         * THREAD                       STANDALONE              fail
         */

        if (!PMC_ROW_DISP_IS_FREE(ri) &&
            !(disp == PMC_DISP_THREAD && PMC_ROW_DISP_IS_THREAD(ri)) &&
            !(disp == PMC_DISP_STANDALONE && PMC_ROW_DISP_IS_STANDALONE(ri)))
                return EBUSY;

        /*
         * All OK
         */

        PMCDBG2(PMC,ALR,2, "can-allocate-row ri=%d mode=%d ok", ri, mode);

        return 0;

}

/*
 * Find a PMC descriptor with user handle 'pmcid' for thread 'td'.
 */

static struct pmc *
pmc_find_pmc_descriptor_in_process(struct pmc_owner *po, pmc_id_t pmcid)
{
        struct pmc *pm;

        KASSERT(PMC_ID_TO_ROWINDEX(pmcid) < md->pmd_npmc,
            ("[pmc,%d] Illegal pmc index %d (max %d)", __LINE__,
                PMC_ID_TO_ROWINDEX(pmcid), md->pmd_npmc));

        LIST_FOREACH(pm, &po->po_pmcs, pm_next)
            if (pm->pm_id == pmcid)
                    return pm;

        return NULL;
}

static int
pmc_find_pmc(pmc_id_t pmcid, struct pmc **pmc)
{

        struct pmc *pm, *opm;
        struct pmc_owner *po;
        struct pmc_process *pp;

        PMCDBG1(PMC,FND,1, "find-pmc id=%d", pmcid);
        if (PMC_ID_TO_ROWINDEX(pmcid) >= md->pmd_npmc)
                return (EINVAL);

        if ((po = pmc_find_owner_descriptor(curthread->td_proc)) == NULL) {
                /*
                 * In case of PMC_F_DESCENDANTS child processes we will not find
                 * the current process in the owners hash list.  Find the owner
                 * process first and from there lookup the po.
                 */
                if ((pp = pmc_find_process_descriptor(curthread->td_proc,
                    PMC_FLAG_NONE)) == NULL) {
                        return ESRCH;
                } else {
                        opm = pp->pp_pmcs[PMC_ID_TO_ROWINDEX(pmcid)].pp_pmc;
                        if (opm == NULL)
                                return ESRCH;
                        if ((opm->pm_flags & (PMC_F_ATTACHED_TO_OWNER|
                            PMC_F_DESCENDANTS)) != (PMC_F_ATTACHED_TO_OWNER|
                            PMC_F_DESCENDANTS))
                                return ESRCH;
                        po = opm->pm_owner;
                }
        }

        if ((pm = pmc_find_pmc_descriptor_in_process(po, pmcid)) == NULL)
                return EINVAL;

        PMCDBG2(PMC,FND,2, "find-pmc id=%d -> pmc=%p", pmcid, pm);

        *pmc = pm;
        return 0;
}

/*
 * Start a PMC.
 */

static int
pmc_start(struct pmc *pm)
{
        enum pmc_mode mode;
        struct pmc_owner *po;
        struct pmc_binding pb;
        struct pmc_classdep *pcd;
        int adjri, error, cpu, ri;

        KASSERT(pm != NULL,
            ("[pmc,%d] null pm", __LINE__));

        mode = PMC_TO_MODE(pm);
        ri   = PMC_TO_ROWINDEX(pm);
        pcd  = pmc_ri_to_classdep(md, ri, &adjri);

        error = 0;

        PMCDBG3(PMC,OPS,1, "start pmc=%p mode=%d ri=%d", pm, mode, ri);

        po = pm->pm_owner;

        /*
         * Disallow PMCSTART if a logfile is required but has not been
         * configured yet.
         */
        if ((pm->pm_flags & PMC_F_NEEDS_LOGFILE) &&
            (po->po_flags & PMC_PO_OWNS_LOGFILE) == 0)
                return (EDOOFUS);       /* programming error */

        /*
         * If this is a sampling mode PMC, log mapping information for
         * the kernel modules that are currently loaded.
         */
        if (PMC_IS_SAMPLING_MODE(PMC_TO_MODE(pm)))
            pmc_log_kernel_mappings(pm);

        if (PMC_IS_VIRTUAL_MODE(mode)) {

                /*
                 * If a PMCATTACH has never been done on this PMC,
                 * attach it to its owner process.
                 */

                if (LIST_EMPTY(&pm->pm_targets))
                        error = (pm->pm_flags & PMC_F_ATTACH_DONE) ? ESRCH :
                            pmc_attach_process(po->po_owner, pm);

                /*
                 * If the PMC is attached to its owner, then force a context
                 * switch to ensure that the MD state gets set correctly.
                 */

                if (error == 0) {
                        pm->pm_state = PMC_STATE_RUNNING;
                        if (pm->pm_flags & PMC_F_ATTACHED_TO_OWNER)
                                pmc_force_context_switch();
                }

                return (error);
        }


        /*
         * A system-wide PMC.
         *
         * Add the owner to the global list if this is a system-wide
         * sampling PMC.
         */

        if (mode == PMC_MODE_SS) {
                if (po->po_sscount == 0) {
                        LIST_INSERT_HEAD(&pmc_ss_owners, po, po_ssnext);
                        atomic_add_rel_int(&pmc_ss_count, 1);
                        PMCDBG1(PMC,OPS,1, "po=%p in global list", po);
                }
                po->po_sscount++;

                /*
                 * Log mapping information for all existing processes in the
                 * system.  Subsequent mappings are logged as they happen;
                 * see pmc_process_mmap().
                 */
                if (po->po_logprocmaps == 0) {
                        pmc_log_all_process_mappings(po);
                        po->po_logprocmaps = 1;
                }
        }

        /*
         * Move to the CPU associated with this
         * PMC, and start the hardware.
         */

        pmc_save_cpu_binding(&pb);

        cpu = PMC_TO_CPU(pm);

        if (!pmc_cpu_is_active(cpu))
                return (ENXIO);

        pmc_select_cpu(cpu);

        /*
         * global PMCs are configured at allocation time
         * so write out the initial value and start the PMC.
         */

        pm->pm_state = PMC_STATE_RUNNING;

        critical_enter();
        if ((error = pcd->pcd_write_pmc(cpu, adjri,
                 PMC_IS_SAMPLING_MODE(mode) ?
                 pm->pm_sc.pm_reloadcount :
                 pm->pm_sc.pm_initial)) == 0) {
                /* If a sampling mode PMC, reset stalled state. */
                if (PMC_IS_SAMPLING_MODE(mode))
                        CPU_CLR_ATOMIC(cpu, &pm->pm_stalled);

                /* Indicate that we desire this to run. Start it. */
                CPU_SET_ATOMIC(cpu, &pm->pm_cpustate);
                error = pcd->pcd_start_pmc(cpu, adjri);
        }
        critical_exit();

        pmc_restore_cpu_binding(&pb);

        return (error);
}

/*
 * Stop a PMC.
 */

static int
pmc_stop(struct pmc *pm)
{
        struct pmc_owner *po;
        struct pmc_binding pb;
        struct pmc_classdep *pcd;
        int adjri, cpu, error, ri;

        KASSERT(pm != NULL, ("[pmc,%d] null pmc", __LINE__));

        PMCDBG3(PMC,OPS,1, "stop pmc=%p mode=%d ri=%d", pm,
            PMC_TO_MODE(pm), PMC_TO_ROWINDEX(pm));

        pm->pm_state = PMC_STATE_STOPPED;

        /*
         * If the PMC is a virtual mode one, changing the state to
         * non-RUNNING is enough to ensure that the PMC never gets
         * scheduled.
         *
         * If this PMC is current running on a CPU, then it will
         * handled correctly at the time its target process is context
         * switched out.
         */

        if (PMC_IS_VIRTUAL_MODE(PMC_TO_MODE(pm)))
                return 0;

        /*
         * A system-mode PMC.  Move to the CPU associated with
         * this PMC, and stop the hardware.  We update the
         * 'initial count' so that a subsequent PMCSTART will
         * resume counting from the current hardware count.
         */

        pmc_save_cpu_binding(&pb);

        cpu = PMC_TO_CPU(pm);

        KASSERT(cpu >= 0 && cpu < pmc_cpu_max(),
            ("[pmc,%d] illegal cpu=%d", __LINE__, cpu));

        if (!pmc_cpu_is_active(cpu))
                return ENXIO;

        pmc_select_cpu(cpu);

        ri = PMC_TO_ROWINDEX(pm);
        pcd = pmc_ri_to_classdep(md, ri, &adjri);

        CPU_CLR_ATOMIC(cpu, &pm->pm_cpustate);
        critical_enter();
        if ((error = pcd->pcd_stop_pmc(cpu, adjri)) == 0)
                error = pcd->pcd_read_pmc(cpu, adjri, &pm->pm_sc.pm_initial);
        critical_exit();

        pmc_restore_cpu_binding(&pb);

        po = pm->pm_owner;

        /* remove this owner from the global list of SS PMC owners */
        if (PMC_TO_MODE(pm) == PMC_MODE_SS) {
                po->po_sscount--;
                if (po->po_sscount == 0) {
                        atomic_subtract_rel_int(&pmc_ss_count, 1);
                        LIST_REMOVE(po, po_ssnext);
                        PMCDBG1(PMC,OPS,2,"po=%p removed from global list", po);
                }
        }

        return (error);
}


#ifdef  HWPMC_DEBUG
static const char *pmc_op_to_name[] = {
#undef  __PMC_OP
#define __PMC_OP(N, D)  #N ,
        __PMC_OPS()
        NULL
};
#endif

/*
 * The syscall interface
 */

#define PMC_GET_SX_XLOCK(...) do {              \
        sx_xlock(&pmc_sx);                      \
        if (pmc_hook == NULL) {                 \
                sx_xunlock(&pmc_sx);            \
                return __VA_ARGS__;             \
        }                                       \
} while (0)

#define PMC_DOWNGRADE_SX() do {                 \
        sx_downgrade(&pmc_sx);                  \
        is_sx_downgraded = 1;                   \
} while (0)

static int
pmc_syscall_handler(struct thread *td, void *syscall_args)
{
        int error, is_sx_downgraded, op;
        struct pmc_syscall_args *c;
        void *pmclog_proc_handle;
        void *arg;

        c = (struct pmc_syscall_args *)syscall_args;
        op = c->pmop_code;
        arg = c->pmop_data;
        if (op == PMC_OP_CONFIGURELOG) {
                /*
                 * We cannot create the logging process inside
                 * pmclog_configure_log() because there is a LOR
                 * between pmc_sx and process structure locks.
                 * Instead, pre-create the process and ignite the loop
                 * if everything is fine, otherwise direct the process
                 * to exit.
                 */
                error = pmclog_proc_create(td, &pmclog_proc_handle);
                if (error != 0)
                        goto done_syscall;
        }

        PMC_GET_SX_XLOCK(ENOSYS);
        is_sx_downgraded = 0;

        PMCDBG3(MOD,PMS,1, "syscall op=%d \"%s\" arg=%p", op,
            pmc_op_to_name[op], arg);

        error = 0;
        atomic_add_int(&pmc_stats.pm_syscalls, 1);

        switch (op) {


        /*
         * Configure a log file.
         *
         * XXX This OP will be reworked.
         */

        case PMC_OP_CONFIGURELOG:
        {
                struct proc *p;
                struct pmc *pm;
                struct pmc_owner *po;
                struct pmc_op_configurelog cl;

                if ((error = copyin(arg, &cl, sizeof(cl))) != 0) {
                        pmclog_proc_ignite(pmclog_proc_handle, NULL);
                        break;
                }

                /* mark this process as owning a log file */
                p = td->td_proc;
                if ((po = pmc_find_owner_descriptor(p)) == NULL)
                        if ((po = pmc_allocate_owner_descriptor(p)) == NULL) {
                                pmclog_proc_ignite(pmclog_proc_handle, NULL);
                                error = ENOMEM;
                                break;
                        }

                /*
                 * If a valid fd was passed in, try to configure that,
                 * otherwise if 'fd' was less than zero and there was
                 * a log file configured, flush its buffers and
                 * de-configure it.
                 */
                if (cl.pm_logfd >= 0) {
                        error = pmclog_configure_log(md, po, cl.pm_logfd);
                        pmclog_proc_ignite(pmclog_proc_handle, error == 0 ?
                            po : NULL);
                } else if (po->po_flags & PMC_PO_OWNS_LOGFILE) {
                        pmclog_proc_ignite(pmclog_proc_handle, NULL);
                        error = pmclog_close(po);
                        if (error == 0) {
                                LIST_FOREACH(pm, &po->po_pmcs, pm_next)
                                    if (pm->pm_flags & PMC_F_NEEDS_LOGFILE &&
                                        pm->pm_state == PMC_STATE_RUNNING)
                                            pmc_stop(pm);
                                error = pmclog_deconfigure_log(po);
                        }
                } else {
                        pmclog_proc_ignite(pmclog_proc_handle, NULL);
                        error = EINVAL;
                }
        }
        break;

        /*
         * Flush a log file.
         */

        case PMC_OP_FLUSHLOG:
        {
                struct pmc_owner *po;

                sx_assert(&pmc_sx, SX_XLOCKED);

                if ((po = pmc_find_owner_descriptor(td->td_proc)) == NULL) {
                        error = EINVAL;
                        break;
                }

                error = pmclog_flush(po);
        }
        break;

        /*
         * Close a log file.
         */

        case PMC_OP_CLOSELOG:
        {
                struct pmc_owner *po;

                sx_assert(&pmc_sx, SX_XLOCKED);

                if ((po = pmc_find_owner_descriptor(td->td_proc)) == NULL) {
                        error = EINVAL;
                        break;
                }

                error = pmclog_close(po);
        }
        break;

        /*
         * Retrieve hardware configuration.
         */

        case PMC_OP_GETCPUINFO: /* CPU information */
        {
                struct pmc_op_getcpuinfo gci;
                struct pmc_classinfo *pci;
                struct pmc_classdep *pcd;
                int cl;

                gci.pm_cputype = md->pmd_cputype;
                gci.pm_ncpu    = pmc_cpu_max();
                gci.pm_npmc    = md->pmd_npmc;
                gci.pm_nclass  = md->pmd_nclass;
                pci = gci.pm_classes;
                pcd = md->pmd_classdep;
                for (cl = 0; cl < md->pmd_nclass; cl++, pci++, pcd++) {
                        pci->pm_caps  = pcd->pcd_caps;
                        pci->pm_class = pcd->pcd_class;
                        pci->pm_width = pcd->pcd_width;
                        pci->pm_num   = pcd->pcd_num;
                }
                error = copyout(&gci, arg, sizeof(gci));
        }
        break;

        /*
         * Retrieve soft events list.
         */
        case PMC_OP_GETDYNEVENTINFO:
        {
                enum pmc_class                  cl;
                enum pmc_event                  ev;
                struct pmc_op_getdyneventinfo   *gei;
                struct pmc_dyn_event_descr      dev;
                struct pmc_soft                 *ps;
                uint32_t                        nevent;

                sx_assert(&pmc_sx, SX_LOCKED);

                gei = (struct pmc_op_getdyneventinfo *) arg;

                if ((error = copyin(&gei->pm_class, &cl, sizeof(cl))) != 0)
                        break;

                /* Only SOFT class is dynamic. */
                if (cl != PMC_CLASS_SOFT) {
                        error = EINVAL;
                        break;
                }

                nevent = 0;
                for (ev = PMC_EV_SOFT_FIRST; (int)ev <= PMC_EV_SOFT_LAST; ev++) {
                        ps = pmc_soft_ev_acquire(ev);
                        if (ps == NULL)
                                continue;
                        bcopy(&ps->ps_ev, &dev, sizeof(dev));
                        pmc_soft_ev_release(ps);

                        error = copyout(&dev,
                            &gei->pm_events[nevent],
                            sizeof(struct pmc_dyn_event_descr));
                        if (error != 0)
                                break;
                        nevent++;
                }
                if (error != 0)
                        break;

                error = copyout(&nevent, &gei->pm_nevent,
                    sizeof(nevent));
        }
        break;

        /*
         * Get module statistics
         */

        case PMC_OP_GETDRIVERSTATS:
        {
                struct pmc_op_getdriverstats gms;

                bcopy(&pmc_stats, &gms, sizeof(gms));
                error = copyout(&gms, arg, sizeof(gms));
        }
        break;


        /*
         * Retrieve module version number
         */

        case PMC_OP_GETMODULEVERSION:
        {
                uint32_t cv, modv;

                /* retrieve the client's idea of the ABI version */
                if ((error = copyin(arg, &cv, sizeof(uint32_t))) != 0)
                        break;
                /* don't service clients newer than our driver */
                modv = PMC_VERSION;
                if ((cv & 0xFFFF0000) > (modv & 0xFFFF0000)) {
                        error = EPROGMISMATCH;
                        break;
                }
                error = copyout(&modv, arg, sizeof(int));
        }
        break;


        /*
         * Retrieve the state of all the PMCs on a given
         * CPU.
         */

        case PMC_OP_GETPMCINFO:
        {
                int ari;
                struct pmc *pm;
                size_t pmcinfo_size;
                uint32_t cpu, n, npmc;
                struct pmc_owner *po;
                struct pmc_binding pb;
                struct pmc_classdep *pcd;
                struct pmc_info *p, *pmcinfo;
                struct pmc_op_getpmcinfo *gpi;

                PMC_DOWNGRADE_SX();

                gpi = (struct pmc_op_getpmcinfo *) arg;

                if ((error = copyin(&gpi->pm_cpu, &cpu, sizeof(cpu))) != 0)
                        break;

                if (cpu >= pmc_cpu_max()) {
                        error = EINVAL;
                        break;
                }

                if (!pmc_cpu_is_active(cpu)) {
                        error = ENXIO;
                        break;
                }

                /* switch to CPU 'cpu' */
                pmc_save_cpu_binding(&pb);
                pmc_select_cpu(cpu);

                npmc = md->pmd_npmc;

                pmcinfo_size = npmc * sizeof(struct pmc_info);
                pmcinfo = malloc(pmcinfo_size, M_PMC, M_WAITOK);

                p = pmcinfo;

                for (n = 0; n < md->pmd_npmc; n++, p++) {

                        pcd = pmc_ri_to_classdep(md, n, &ari);

                        KASSERT(pcd != NULL,
                            ("[pmc,%d] null pcd ri=%d", __LINE__, n));

                        if ((error = pcd->pcd_describe(cpu, ari, p, &pm)) != 0)
                                break;

                        if (PMC_ROW_DISP_IS_STANDALONE(n))
                                p->pm_rowdisp = PMC_DISP_STANDALONE;
                        else if (PMC_ROW_DISP_IS_THREAD(n))
                                p->pm_rowdisp = PMC_DISP_THREAD;
                        else
                                p->pm_rowdisp = PMC_DISP_FREE;

                        p->pm_ownerpid = -1;

                        if (pm == NULL) /* no PMC associated */
                                continue;

                        po = pm->pm_owner;

                        KASSERT(po->po_owner != NULL,
                            ("[pmc,%d] pmc_owner had a null proc pointer",
                                __LINE__));

                        p->pm_ownerpid = po->po_owner->p_pid;
                        p->pm_mode     = PMC_TO_MODE(pm);
                        p->pm_event    = pm->pm_event;
                        p->pm_flags    = pm->pm_flags;

                        if (PMC_IS_SAMPLING_MODE(PMC_TO_MODE(pm)))
                                p->pm_reloadcount =
                                    pm->pm_sc.pm_reloadcount;
                }

                pmc_restore_cpu_binding(&pb);

                /* now copy out the PMC info collected */
                if (error == 0)
                        error = copyout(pmcinfo, &gpi->pm_pmcs, pmcinfo_size);

                free(pmcinfo, M_PMC);
        }
        break;


        /*
         * Set the administrative state of a PMC.  I.e. whether
         * the PMC is to be used or not.
         */

        case PMC_OP_PMCADMIN:
        {
                int cpu, ri;
                enum pmc_state request;
                struct pmc_cpu *pc;
                struct pmc_hw *phw;
                struct pmc_op_pmcadmin pma;
                struct pmc_binding pb;

                sx_assert(&pmc_sx, SX_XLOCKED);

                KASSERT(td == curthread,
                    ("[pmc,%d] td != curthread", __LINE__));

                error = priv_check(td, PRIV_PMC_MANAGE);
                if (error)
                        break;

                if ((error = copyin(arg, &pma, sizeof(pma))) != 0)
                        break;

                cpu = pma.pm_cpu;

                if (cpu < 0 || cpu >= (int) pmc_cpu_max()) {
                        error = EINVAL;
                        break;
                }

                if (!pmc_cpu_is_active(cpu)) {
                        error = ENXIO;
                        break;
                }

                request = pma.pm_state;

                if (request != PMC_STATE_DISABLED &&
                    request != PMC_STATE_FREE) {
                        error = EINVAL;
                        break;
                }

                ri = pma.pm_pmc; /* pmc id == row index */
                if (ri < 0 || ri >= (int) md->pmd_npmc) {
                        error = EINVAL;
                        break;
                }

                /*
                 * We can't disable a PMC with a row-index allocated
                 * for process virtual PMCs.
                 */

                if (PMC_ROW_DISP_IS_THREAD(ri) &&
                    request == PMC_STATE_DISABLED) {
                        error = EBUSY;
                        break;
                }

                /*
                 * otherwise, this PMC on this CPU is either free or
                 * in system-wide mode.
                 */

                pmc_save_cpu_binding(&pb);
                pmc_select_cpu(cpu);

                pc  = pmc_pcpu[cpu];
                phw = pc->pc_hwpmcs[ri];

                /*
                 * XXX do we need some kind of 'forced' disable?
                 */

                if (phw->phw_pmc == NULL) {
                        if (request == PMC_STATE_DISABLED &&
                            (phw->phw_state & PMC_PHW_FLAG_IS_ENABLED)) {
                                phw->phw_state &= ~PMC_PHW_FLAG_IS_ENABLED;
                                PMC_MARK_ROW_STANDALONE(ri);
                        } else if (request == PMC_STATE_FREE &&
                            (phw->phw_state & PMC_PHW_FLAG_IS_ENABLED) == 0) {
                                phw->phw_state |=  PMC_PHW_FLAG_IS_ENABLED;
                                PMC_UNMARK_ROW_STANDALONE(ri);
                        }
                        /* other cases are a no-op */
                } else
                        error = EBUSY;

                pmc_restore_cpu_binding(&pb);
        }
        break;


        /*
         * Allocate a PMC.
         */

        case PMC_OP_PMCALLOCATE:
        {
                int adjri, n;
                u_int cpu;
                uint32_t caps;
                struct pmc *pmc;
                enum pmc_mode mode;
                struct pmc_hw *phw;
                struct pmc_binding pb;
                struct pmc_classdep *pcd;
                struct pmc_op_pmcallocate pa;

                if ((error = copyin(arg, &pa, sizeof(pa))) != 0)
                        break;

                caps = pa.pm_caps;
                mode = pa.pm_mode;
                cpu  = pa.pm_cpu;

                if ((mode != PMC_MODE_SS  &&  mode != PMC_MODE_SC  &&
                     mode != PMC_MODE_TS  &&  mode != PMC_MODE_TC) ||
                    (cpu != (u_int) PMC_CPU_ANY && cpu >= pmc_cpu_max())) {
                        error = EINVAL;
                        break;
                }

                /*
                 * Virtual PMCs should only ask for a default CPU.
                 * System mode PMCs need to specify a non-default CPU.
                 */

                if ((PMC_IS_VIRTUAL_MODE(mode) && cpu != (u_int) PMC_CPU_ANY) ||
                    (PMC_IS_SYSTEM_MODE(mode) && cpu == (u_int) PMC_CPU_ANY)) {
                        error = EINVAL;
                        break;
                }

                /*
                 * Check that an inactive CPU is not being asked for.
                 */

                if (PMC_IS_SYSTEM_MODE(mode) && !pmc_cpu_is_active(cpu)) {
                        error = ENXIO;
                        break;
                }

                /*
                 * Refuse an allocation for a system-wide PMC if this
                 * process has been jailed, or if this process lacks
                 * super-user credentials and the sysctl tunable
                 * 'security.bsd.unprivileged_syspmcs' is zero.
                 */

                if (PMC_IS_SYSTEM_MODE(mode)) {
                        if (jailed(curthread->td_ucred)) {
                                error = EPERM;
                                break;
                        }
                        if (!pmc_unprivileged_syspmcs) {
                                error = priv_check(curthread,
                                    PRIV_PMC_SYSTEM);
                                if (error)
                                        break;
                        }
                }

                /*
                 * Look for valid values for 'pm_flags'
                 */

                if ((pa.pm_flags & ~(PMC_F_DESCENDANTS | PMC_F_LOG_PROCCSW |
                    PMC_F_LOG_PROCEXIT | PMC_F_CALLCHAIN)) != 0) {
                        error = EINVAL;
                        break;
                }

                /* process logging options are not allowed for system PMCs */
                if (PMC_IS_SYSTEM_MODE(mode) && (pa.pm_flags &
                    (PMC_F_LOG_PROCCSW | PMC_F_LOG_PROCEXIT))) {
                        error = EINVAL;
                        break;
                }

                /*
                 * All sampling mode PMCs need to be able to interrupt the
                 * CPU.
                 */
                if (PMC_IS_SAMPLING_MODE(mode))
                        caps |= PMC_CAP_INTERRUPT;

                /* A valid class specifier should have been passed in. */
                for (n = 0; n < md->pmd_nclass; n++)
                        if (md->pmd_classdep[n].pcd_class == pa.pm_class)
                                break;
                if (n == md->pmd_nclass) {
                        error = EINVAL;
                        break;
                }

                /* The requested PMC capabilities should be feasible. */
                if ((md->pmd_classdep[n].pcd_caps & caps) != caps) {
                        error = EOPNOTSUPP;
                        break;
                }

                PMCDBG4(PMC,ALL,2, "event=%d caps=0x%x mode=%d cpu=%d",
                    pa.pm_ev, caps, mode, cpu);

                pmc = pmc_allocate_pmc_descriptor();
                pmc->pm_id    = PMC_ID_MAKE_ID(cpu,pa.pm_mode,pa.pm_class,
                    PMC_ID_INVALID);
                pmc->pm_event = pa.pm_ev;
                pmc->pm_state = PMC_STATE_FREE;
                pmc->pm_caps  = caps;
                pmc->pm_flags = pa.pm_flags;

                /* switch thread to CPU 'cpu' */
                pmc_save_cpu_binding(&pb);

#define PMC_IS_SHAREABLE_PMC(cpu, n)                            \
        (pmc_pcpu[(cpu)]->pc_hwpmcs[(n)]->phw_state &           \
         PMC_PHW_FLAG_IS_SHAREABLE)
#define PMC_IS_UNALLOCATED(cpu, n)                              \
        (pmc_pcpu[(cpu)]->pc_hwpmcs[(n)]->phw_pmc == NULL)

                if (PMC_IS_SYSTEM_MODE(mode)) {
                        pmc_select_cpu(cpu);
                        for (n = 0; n < (int) md->pmd_npmc; n++) {
                                pcd = pmc_ri_to_classdep(md, n, &adjri);
                                if (pmc_can_allocate_row(n, mode) == 0 &&
                                    pmc_can_allocate_rowindex(
                                            curthread->td_proc, n, cpu) == 0 &&
                                    (PMC_IS_UNALLOCATED(cpu, n) ||
                                     PMC_IS_SHAREABLE_PMC(cpu, n)) &&
                                    pcd->pcd_allocate_pmc(cpu, adjri, pmc,
                                        &pa) == 0)
                                        break;
                        }
                } else {
                        /* Process virtual mode */
                        for (n = 0; n < (int) md->pmd_npmc; n++) {
                                pcd = pmc_ri_to_classdep(md, n, &adjri);
                                if (pmc_can_allocate_row(n, mode) == 0 &&
                                    pmc_can_allocate_rowindex(
                                            curthread->td_proc, n,
                                            PMC_CPU_ANY) == 0 &&
                                    pcd->pcd_allocate_pmc(curthread->td_oncpu,
                                        adjri, pmc, &pa) == 0)
                                        break;
                        }
                }

#undef  PMC_IS_UNALLOCATED
#undef  PMC_IS_SHAREABLE_PMC

                pmc_restore_cpu_binding(&pb);

                if (n == (int) md->pmd_npmc) {
                        pmc_destroy_pmc_descriptor(pmc);
                        pmc = NULL;
                        error = EINVAL;
                        break;
                }

                /* Fill in the correct value in the ID field */
                pmc->pm_id = PMC_ID_MAKE_ID(cpu,mode,pa.pm_class,n);

                PMCDBG5(PMC,ALL,2, "ev=%d class=%d mode=%d n=%d -> pmcid=%x",
                    pmc->pm_event, pa.pm_class, mode, n, pmc->pm_id);

                /* Process mode PMCs with logging enabled need log files */
                if (pmc->pm_flags & (PMC_F_LOG_PROCEXIT | PMC_F_LOG_PROCCSW))
                        pmc->pm_flags |= PMC_F_NEEDS_LOGFILE;

                /* All system mode sampling PMCs require a log file */
                if (PMC_IS_SAMPLING_MODE(mode) && PMC_IS_SYSTEM_MODE(mode))
                        pmc->pm_flags |= PMC_F_NEEDS_LOGFILE;

                /*
                 * Configure global pmc's immediately
                 */

                if (PMC_IS_SYSTEM_MODE(PMC_TO_MODE(pmc))) {

                        pmc_save_cpu_binding(&pb);
                        pmc_select_cpu(cpu);

                        phw = pmc_pcpu[cpu]->pc_hwpmcs[n];
                        pcd = pmc_ri_to_classdep(md, n, &adjri);

                        if ((phw->phw_state & PMC_PHW_FLAG_IS_ENABLED) == 0 ||
                            (error = pcd->pcd_config_pmc(cpu, adjri, pmc)) != 0) {
                                (void) pcd->pcd_release_pmc(cpu, adjri, pmc);
                                pmc_destroy_pmc_descriptor(pmc);
                                pmc = NULL;
                                pmc_restore_cpu_binding(&pb);
                                error = EPERM;
                                break;
                        }

                        pmc_restore_cpu_binding(&pb);
                }

                pmc->pm_state    = PMC_STATE_ALLOCATED;

                /*
                 * mark row disposition
                 */

                if (PMC_IS_SYSTEM_MODE(mode))
                        PMC_MARK_ROW_STANDALONE(n);
                else
                        PMC_MARK_ROW_THREAD(n);

                /*
                 * Register this PMC with the current thread as its owner.
                 */

                if ((error =
                    pmc_register_owner(curthread->td_proc, pmc)) != 0) {
                        pmc_release_pmc_descriptor(pmc);
                        pmc_destroy_pmc_descriptor(pmc);
                        pmc = NULL;
                        break;
                }

                /*
                 * Return the allocated index.
                 */

                pa.pm_pmcid = pmc->pm_id;

                error = copyout(&pa, arg, sizeof(pa));
        }
        break;


        /*
         * Attach a PMC to a process.
         */

        case PMC_OP_PMCATTACH:
        {
                struct pmc *pm;
                struct proc *p;
                struct pmc_op_pmcattach a;

                sx_assert(&pmc_sx, SX_XLOCKED);

                if ((error = copyin(arg, &a, sizeof(a))) != 0)
                        break;

                if (a.pm_pid < 0) {
                        error = EINVAL;
                        break;
                } else if (a.pm_pid == 0)
                        a.pm_pid = td->td_proc->p_pid;

                if ((error = pmc_find_pmc(a.pm_pmc, &pm)) != 0)
                        break;

                if (PMC_IS_SYSTEM_MODE(PMC_TO_MODE(pm))) {
                        error = EINVAL;
                        break;
                }

                /* PMCs may be (re)attached only when allocated or stopped */
                if (pm->pm_state == PMC_STATE_RUNNING) {
                        error = EBUSY;
                        break;
                } else if (pm->pm_state != PMC_STATE_ALLOCATED &&
                    pm->pm_state != PMC_STATE_STOPPED) {
                        error = EINVAL;
                        break;
                }

                /* lookup pid */
                if ((p = pfind(a.pm_pid)) == NULL) {
                        error = ESRCH;
                        break;
                }

                /*
                 * Ignore processes that are working on exiting.
                 */
                if (p->p_flag & P_WEXIT) {
                        error = ESRCH;
                        PROC_UNLOCK(p); /* pfind() returns a locked process */
                        break;
                }

                /*
                 * we are allowed to attach a PMC to a process if
                 * we can debug it.
                 */
                error = p_candebug(curthread, p);

                PROC_UNLOCK(p);

                if (error == 0)
                        error = pmc_attach_process(p, pm);
        }
        break;


        /*
         * Detach an attached PMC from a process.
         */

        case PMC_OP_PMCDETACH:
        {
                struct pmc *pm;
                struct proc *p;
                struct pmc_op_pmcattach a;

                if ((error = copyin(arg, &a, sizeof(a))) != 0)
                        break;

                if (a.pm_pid < 0) {
                        error = EINVAL;
                        break;
                } else if (a.pm_pid == 0)
                        a.pm_pid = td->td_proc->p_pid;

                if ((error = pmc_find_pmc(a.pm_pmc, &pm)) != 0)
                        break;

                if ((p = pfind(a.pm_pid)) == NULL) {
                        error = ESRCH;
                        break;
                }

                /*
                 * Treat processes that are in the process of exiting
                 * as if they were not present.
                 */

                if (p->p_flag & P_WEXIT)
                        error = ESRCH;

                PROC_UNLOCK(p); /* pfind() returns a locked process */

                if (error == 0)
                        error = pmc_detach_process(p, pm);
        }
        break;


        /*
         * Retrieve the MSR number associated with the counter
         * 'pmc_id'.  This allows processes to directly use RDPMC
         * instructions to read their PMCs, without the overhead of a
         * system call.
         */

        case PMC_OP_PMCGETMSR:
        {
                int adjri, ri;
                struct pmc *pm;
                struct pmc_target *pt;
                struct pmc_op_getmsr gm;
                struct pmc_classdep *pcd;

                PMC_DOWNGRADE_SX();

                if ((error = copyin(arg, &gm, sizeof(gm))) != 0)
                        break;

                if ((error = pmc_find_pmc(gm.pm_pmcid, &pm)) != 0)
                        break;

                /*
                 * The allocated PMC has to be a process virtual PMC,
                 * i.e., of type MODE_T[CS].  Global PMCs can only be
                 * read using the PMCREAD operation since they may be
                 * allocated on a different CPU than the one we could
                 * be running on at the time of the RDPMC instruction.
                 *
                 * The GETMSR operation is not allowed for PMCs that
                 * are inherited across processes.
                 */

                if (!PMC_IS_VIRTUAL_MODE(PMC_TO_MODE(pm)) ||
                    (pm->pm_flags & PMC_F_DESCENDANTS)) {
                        error = EINVAL;
                        break;
                }

                /*
                 * It only makes sense to use a RDPMC (or its
                 * equivalent instruction on non-x86 architectures) on
                 * a process that has allocated and attached a PMC to
                 * itself.  Conversely the PMC is only allowed to have
                 * one process attached to it -- its owner.
                 */

                if ((pt = LIST_FIRST(&pm->pm_targets)) == NULL ||
                    LIST_NEXT(pt, pt_next) != NULL ||
                    pt->pt_process->pp_proc != pm->pm_owner->po_owner) {
                        error = EINVAL;
                        break;
                }

                ri = PMC_TO_ROWINDEX(pm);
                pcd = pmc_ri_to_classdep(md, ri, &adjri);

                /* PMC class has no 'GETMSR' support */
                if (pcd->pcd_get_msr == NULL) {
                        error = ENOSYS;
                        break;
                }

                if ((error = (*pcd->pcd_get_msr)(adjri, &gm.pm_msr)) < 0)
                        break;

                if ((error = copyout(&gm, arg, sizeof(gm))) < 0)
                        break;

                /*
                 * Mark our process as using MSRs.  Update machine
                 * state using a forced context switch.
                 */

                pt->pt_process->pp_flags |= PMC_PP_ENABLE_MSR_ACCESS;
                pmc_force_context_switch();

        }
        break;

        /*
         * Release an allocated PMC
         */

        case PMC_OP_PMCRELEASE:
        {
                pmc_id_t pmcid;
                struct pmc *pm;
                struct pmc_owner *po;
                struct pmc_op_simple sp;

                /*
                 * Find PMC pointer for the named PMC.
                 *
                 * Use pmc_release_pmc_descriptor() to switch off the
                 * PMC, remove all its target threads, and remove the
                 * PMC from its owner's list.
                 *
                 * Remove the owner record if this is the last PMC
                 * owned.
                 *
                 * Free up space.
                 */

                if ((error = copyin(arg, &sp, sizeof(sp))) != 0)
                        break;

                pmcid = sp.pm_pmcid;

                if ((error = pmc_find_pmc(pmcid, &pm)) != 0)
                        break;

                po = pm->pm_owner;
                pmc_release_pmc_descriptor(pm);
                pmc_maybe_remove_owner(po);
                pmc_destroy_pmc_descriptor(pm);
        }
        break;


        /*
         * Read and/or write a PMC.
         */

        case PMC_OP_PMCRW:
        {
                int adjri;
                struct pmc *pm;
                uint32_t cpu, ri;
                pmc_value_t oldvalue;
                struct pmc_binding pb;
                struct pmc_op_pmcrw prw;
                struct pmc_classdep *pcd;
                struct pmc_op_pmcrw *pprw;

                PMC_DOWNGRADE_SX();

                if ((error = copyin(arg, &prw, sizeof(prw))) != 0)
                        break;

                ri = 0;
                PMCDBG2(PMC,OPS,1, "rw id=%d flags=0x%x", prw.pm_pmcid,
                    prw.pm_flags);

                /* must have at least one flag set */
                if ((prw.pm_flags & (PMC_F_OLDVALUE|PMC_F_NEWVALUE)) == 0) {
                        error = EINVAL;
                        break;
                }

                /* locate pmc descriptor */
                if ((error = pmc_find_pmc(prw.pm_pmcid, &pm)) != 0)
                        break;

                /* Can't read a PMC that hasn't been started. */
                if (pm->pm_state != PMC_STATE_ALLOCATED &&
                    pm->pm_state != PMC_STATE_STOPPED &&
                    pm->pm_state != PMC_STATE_RUNNING) {
                        error = EINVAL;
                        break;
                }

                /* writing a new value is allowed only for 'STOPPED' pmcs */
                if (pm->pm_state == PMC_STATE_RUNNING &&
                    (prw.pm_flags & PMC_F_NEWVALUE)) {
                        error = EBUSY;
                        break;
                }

                if (PMC_IS_VIRTUAL_MODE(PMC_TO_MODE(pm))) {

                        /*
                         * If this PMC is attached to its owner (i.e.,
                         * the process requesting this operation) and
                         * is running, then attempt to get an
                         * upto-date reading from hardware for a READ.
                         * Writes are only allowed when the PMC is
                         * stopped, so only update the saved value
                         * field.
                         *
                         * If the PMC is not running, or is not
                         * attached to its owner, read/write to the
                         * savedvalue field.
                         */

                        ri = PMC_TO_ROWINDEX(pm);
                        pcd = pmc_ri_to_classdep(md, ri, &adjri);

                        mtx_pool_lock_spin(pmc_mtxpool, pm);
                        cpu = curthread->td_oncpu;

                        if (prw.pm_flags & PMC_F_OLDVALUE) {
                                if ((pm->pm_flags & PMC_F_ATTACHED_TO_OWNER) &&
                                    (pm->pm_state == PMC_STATE_RUNNING))
                                        error = (*pcd->pcd_read_pmc)(cpu, adjri,
                                            &oldvalue);
                                else
                                        oldvalue = pm->pm_gv.pm_savedvalue;
                        }
                        if (prw.pm_flags & PMC_F_NEWVALUE)
                                pm->pm_gv.pm_savedvalue = prw.pm_value;

                        mtx_pool_unlock_spin(pmc_mtxpool, pm);

                } else { /* System mode PMCs */
                        cpu = PMC_TO_CPU(pm);
                        ri  = PMC_TO_ROWINDEX(pm);
                        pcd = pmc_ri_to_classdep(md, ri, &adjri);

                        if (!pmc_cpu_is_active(cpu)) {
                                error = ENXIO;
                                break;
                        }

                        /* move this thread to CPU 'cpu' */
                        pmc_save_cpu_binding(&pb);
                        pmc_select_cpu(cpu);

                        critical_enter();
                        /* save old value */
                        if (prw.pm_flags & PMC_F_OLDVALUE)
                                if ((error = (*pcd->pcd_read_pmc)(cpu, adjri,
                                         &oldvalue)))
                                        goto error;
                        /* write out new value */
                        if (prw.pm_flags & PMC_F_NEWVALUE)
                                error = (*pcd->pcd_write_pmc)(cpu, adjri,
                                    prw.pm_value);
                error:
                        critical_exit();
                        pmc_restore_cpu_binding(&pb);
                        if (error)
                                break;
                }

                pprw = (struct pmc_op_pmcrw *) arg;

#ifdef  HWPMC_DEBUG
                if (prw.pm_flags & PMC_F_NEWVALUE)
                        PMCDBG3(PMC,OPS,2, "rw id=%d new %jx -> old %jx",
                            ri, prw.pm_value, oldvalue);
                else if (prw.pm_flags & PMC_F_OLDVALUE)
                        PMCDBG2(PMC,OPS,2, "rw id=%d -> old %jx", ri, oldvalue);
#endif

                /* return old value if requested */
                if (prw.pm_flags & PMC_F_OLDVALUE)
                        if ((error = copyout(&oldvalue, &pprw->pm_value,
                                 sizeof(prw.pm_value))))
                                break;

        }
        break;


        /*
         * Set the sampling rate for a sampling mode PMC and the
         * initial count for a counting mode PMC.
         */

        case PMC_OP_PMCSETCOUNT:
        {
                struct pmc *pm;
                struct pmc_op_pmcsetcount sc;

                PMC_DOWNGRADE_SX();

                if ((error = copyin(arg, &sc, sizeof(sc))) != 0)
                        break;

                if ((error = pmc_find_pmc(sc.pm_pmcid, &pm)) != 0)
                        break;

                if (pm->pm_state == PMC_STATE_RUNNING) {
                        error = EBUSY;
                        break;
                }

                if (PMC_IS_SAMPLING_MODE(PMC_TO_MODE(pm)))
                        pm->pm_sc.pm_reloadcount = sc.pm_count;
                else
                        pm->pm_sc.pm_initial = sc.pm_count;
        }
        break;


        /*
         * Start a PMC.
         */

        case PMC_OP_PMCSTART:
        {
                pmc_id_t pmcid;
                struct pmc *pm;
                struct pmc_op_simple sp;

                sx_assert(&pmc_sx, SX_XLOCKED);

                if ((error = copyin(arg, &sp, sizeof(sp))) != 0)
                        break;

                pmcid = sp.pm_pmcid;

                if ((error = pmc_find_pmc(pmcid, &pm)) != 0)
                        break;

                KASSERT(pmcid == pm->pm_id,
                    ("[pmc,%d] pmcid %x != id %x", __LINE__,
                        pm->pm_id, pmcid));

                if (pm->pm_state == PMC_STATE_RUNNING) /* already running */
                        break;
                else if (pm->pm_state != PMC_STATE_STOPPED &&
                    pm->pm_state != PMC_STATE_ALLOCATED) {
                        error = EINVAL;
                        break;
                }

                error = pmc_start(pm);
        }
        break;


        /*
         * Stop a PMC.
         */

        case PMC_OP_PMCSTOP:
        {
                pmc_id_t pmcid;
                struct pmc *pm;
                struct pmc_op_simple sp;

                PMC_DOWNGRADE_SX();

                if ((error = copyin(arg, &sp, sizeof(sp))) != 0)
                        break;

                pmcid = sp.pm_pmcid;

                /*
                 * Mark the PMC as inactive and invoke the MD stop
                 * routines if needed.
                 */

                if ((error = pmc_find_pmc(pmcid, &pm)) != 0)
                        break;

                KASSERT(pmcid == pm->pm_id,
                    ("[pmc,%d] pmc id %x != pmcid %x", __LINE__,
                        pm->pm_id, pmcid));

                if (pm->pm_state == PMC_STATE_STOPPED) /* already stopped */
                        break;
                else if (pm->pm_state != PMC_STATE_RUNNING) {
                        error = EINVAL;
                        break;
                }

                error = pmc_stop(pm);
        }
        break;


        /*
         * Write a user supplied value to the log file.
         */

        case PMC_OP_WRITELOG:
        {
                struct pmc_op_writelog wl;
                struct pmc_owner *po;

                PMC_DOWNGRADE_SX();

                if ((error = copyin(arg, &wl, sizeof(wl))) != 0)
                        break;

                if ((po = pmc_find_owner_descriptor(td->td_proc)) == NULL) {
                        error = EINVAL;
                        break;
                }

                if ((po->po_flags & PMC_PO_OWNS_LOGFILE) == 0) {
                        error = EINVAL;
                        break;
                }

                error = pmclog_process_userlog(po, &wl);
        }
        break;


        default:
                error = EINVAL;
                break;
        }

        if (is_sx_downgraded)
                sx_sunlock(&pmc_sx);
        else
                sx_xunlock(&pmc_sx);
done_syscall:
        if (error)
                atomic_add_int(&pmc_stats.pm_syscall_errors, 1);

        return (error);
}

/*
 * Helper functions
 */


/*
 * Mark the thread as needing callchain capture and post an AST.  The
 * actual callchain capture will be done in a context where it is safe
 * to take page faults.
 */

static void
pmc_post_callchain_callback(void)
{
        struct thread *td;

        td = curthread;

        /*
         * If there is multiple PMCs for the same interrupt ignore new post
         */
        if (td->td_pflags & TDP_CALLCHAIN)
                return;

        /*
         * Mark this thread as needing callchain capture.
         * `td->td_pflags' will be safe to touch because this thread
         * was in user space when it was interrupted.
         */
        td->td_pflags |= TDP_CALLCHAIN;

        /*
         * Don't let this thread migrate between CPUs until callchain
         * capture completes.
         */
        sched_pin();

        return;
}

/*
 * Interrupt processing.
 *
 * Find a free slot in the per-cpu array of samples and capture the
 * current callchain there.  If a sample was successfully added, a bit
 * is set in mask 'pmc_cpumask' denoting that the DO_SAMPLES hook
 * needs to be invoked from the clock handler.
 *
 * This function is meant to be called from an NMI handler.  It cannot
 * use any of the locking primitives supplied by the OS.
 */

int
pmc_process_interrupt(int cpu, int ring, struct pmc *pm, struct trapframe *tf,
    int inuserspace)
{
        int error, callchaindepth;
        struct thread *td;
        struct pmc_sample *ps;
        struct pmc_samplebuffer *psb;

        error = 0;

        /*
         * Allocate space for a sample buffer.
         */
        psb = pmc_pcpu[cpu]->pc_sb[ring];

        ps = psb->ps_write;
        if (ps->ps_nsamples) {  /* in use, reader hasn't caught up */
                CPU_SET_ATOMIC(cpu, &pm->pm_stalled);
                atomic_add_int(&pmc_stats.pm_intr_bufferfull, 1);
                PMCDBG6(SAM,INT,1,"(spc) cpu=%d pm=%p tf=%p um=%d wr=%d rd=%d",
                    cpu, pm, (void *) tf, inuserspace,
                    (int) (psb->ps_write - psb->ps_samples),
                    (int) (psb->ps_read - psb->ps_samples));
                callchaindepth = 1;
                error = ENOMEM;
                goto done;
        }


        /* Fill in entry. */
        PMCDBG6(SAM,INT,1,"cpu=%d pm=%p tf=%p um=%d wr=%d rd=%d", cpu, pm,
            (void *) tf, inuserspace,
            (int) (psb->ps_write - psb->ps_samples),
            (int) (psb->ps_read - psb->ps_samples));

        KASSERT(pm->pm_runcount >= 0,
            ("[pmc,%d] pm=%p runcount %d", __LINE__, (void *) pm,
                pm->pm_runcount));

        atomic_add_rel_int(&pm->pm_runcount, 1);        /* hold onto PMC */

        ps->ps_pmc = pm;
        if ((td = curthread) && td->td_proc)
                ps->ps_pid = td->td_proc->p_pid;
        else
                ps->ps_pid = -1;
        ps->ps_cpu = cpu;
        ps->ps_td = td;
        ps->ps_flags = inuserspace ? PMC_CC_F_USERSPACE : 0;

        callchaindepth = (pm->pm_flags & PMC_F_CALLCHAIN) ?
            pmc_callchaindepth : 1;

        if (callchaindepth == 1)
                ps->ps_pc[0] = PMC_TRAPFRAME_TO_PC(tf);
        else {
                /*
                 * Kernel stack traversals can be done immediately,
                 * while we defer to an AST for user space traversals.
                 */
                if (!inuserspace) {
                        callchaindepth =
                            pmc_save_kernel_callchain(ps->ps_pc,
                                callchaindepth, tf);
                } else {
                        pmc_post_callchain_callback();
                        callchaindepth = PMC_SAMPLE_INUSE;
                }
        }

        ps->ps_nsamples = callchaindepth;       /* mark entry as in use */

        /* increment write pointer, modulo ring buffer size */
        ps++;
        if (ps == psb->ps_fence)
                psb->ps_write = psb->ps_samples;
        else
                psb->ps_write = ps;

 done:
        /* mark CPU as needing processing */
        if (callchaindepth != PMC_SAMPLE_INUSE)
                CPU_SET_ATOMIC(cpu, &pmc_cpumask);

        return (error);
}

/*
 * Capture a user call chain.  This function will be called from ast()
 * before control returns to userland and before the process gets
 * rescheduled.
 */

static void
pmc_capture_user_callchain(int cpu, int ring, struct trapframe *tf)
{
        struct pmc *pm;
        struct thread *td;
        struct pmc_sample *ps, *ps_end;
        struct pmc_samplebuffer *psb;
#ifdef  INVARIANTS
        int ncallchains;
        int nfree;
#endif

        psb = pmc_pcpu[cpu]->pc_sb[ring];
        td = curthread;

        KASSERT(td->td_pflags & TDP_CALLCHAIN,
            ("[pmc,%d] Retrieving callchain for thread that doesn't want it",
                __LINE__));

#ifdef  INVARIANTS
        ncallchains = 0;
        nfree = 0;
#endif

        /*
         * Iterate through all deferred callchain requests.
         * Walk from the current read pointer to the current
         * write pointer.
         */

        ps = psb->ps_read;
        ps_end = psb->ps_write;
        do {
#ifdef  INVARIANTS
                if ((ps->ps_pmc == NULL) ||
                    (ps->ps_pmc->pm_state != PMC_STATE_RUNNING))
                        nfree++;
#endif
                if (ps->ps_nsamples != PMC_SAMPLE_INUSE)
                        goto next;
                if (ps->ps_td != td)
                        goto next;

                KASSERT(ps->ps_cpu == cpu,
                    ("[pmc,%d] cpu mismatch ps_cpu=%d pcpu=%d", __LINE__,
                        ps->ps_cpu, PCPU_GET(cpuid)));

                pm = ps->ps_pmc;

                KASSERT(pm->pm_flags & PMC_F_CALLCHAIN,
                    ("[pmc,%d] Retrieving callchain for PMC that doesn't "
                        "want it", __LINE__));

                KASSERT(pm->pm_runcount > 0,
                    ("[pmc,%d] runcount %d", __LINE__, pm->pm_runcount));

                /*
                 * Retrieve the callchain and mark the sample buffer
                 * as 'processable' by the timer tick sweep code.
                 */
                ps->ps_nsamples = pmc_save_user_callchain(ps->ps_pc,
                    pmc_callchaindepth, tf);

#ifdef  INVARIANTS
                ncallchains++;
#endif

next:
                /* increment the pointer, modulo sample ring size */
                if (++ps == psb->ps_fence)
                        ps = psb->ps_samples;
        } while (ps != ps_end);

#ifdef  INVARIANTS
        KASSERT(ncallchains > 0 || nfree > 0,
            ("[pmc,%d] cpu %d didn't find a sample to collect", __LINE__,
                cpu));
#endif

        KASSERT(td->td_pinned == 1,
            ("[pmc,%d] invalid td_pinned value", __LINE__));
        sched_unpin();  /* Can migrate safely now. */

        /* mark CPU as needing processing */
        CPU_SET_ATOMIC(cpu, &pmc_cpumask);

        return;
}

/*
 * Process saved PC samples.
 */

static void
pmc_process_samples(int cpu, int ring)
{
        struct pmc *pm;
        int adjri, n;
        struct thread *td;
        struct pmc_owner *po;
        struct pmc_sample *ps;
        struct pmc_classdep *pcd;
        struct pmc_samplebuffer *psb;

        KASSERT(PCPU_GET(cpuid) == cpu,
            ("[pmc,%d] not on the correct CPU pcpu=%d cpu=%d", __LINE__,
                PCPU_GET(cpuid), cpu));

        psb = pmc_pcpu[cpu]->pc_sb[ring];

        for (n = 0; n < pmc_nsamples; n++) { /* bound on #iterations */

                ps = psb->ps_read;
                if (ps->ps_nsamples == PMC_SAMPLE_FREE)
                        break;

                pm = ps->ps_pmc;

                KASSERT(pm->pm_runcount > 0,
                    ("[pmc,%d] pm=%p runcount %d", __LINE__, (void *) pm,
                        pm->pm_runcount));

                po = pm->pm_owner;

                KASSERT(PMC_IS_SAMPLING_MODE(PMC_TO_MODE(pm)),
                    ("[pmc,%d] pmc=%p non-sampling mode=%d", __LINE__,
                        pm, PMC_TO_MODE(pm)));

                /* Ignore PMCs that have been switched off */
                if (pm->pm_state != PMC_STATE_RUNNING)
                        goto entrydone;

                /* If there is a pending AST wait for completion */
                if (ps->ps_nsamples == PMC_SAMPLE_INUSE) {
                        /* Need a rescan at a later time. */
                        CPU_SET_ATOMIC(cpu, &pmc_cpumask);
                        break;
                }

                PMCDBG6(SAM,OPS,1,"cpu=%d pm=%p n=%d fl=%x wr=%d rd=%d", cpu,
                    pm, ps->ps_nsamples, ps->ps_flags,
                    (int) (psb->ps_write - psb->ps_samples),
                    (int) (psb->ps_read - psb->ps_samples));

                /*
                 * If this is a process-mode PMC that is attached to
                 * its owner, and if the PC is in user mode, update
                 * profiling statistics like timer-based profiling
                 * would have done.
                 */
                if (pm->pm_flags & PMC_F_ATTACHED_TO_OWNER) {
                        if (ps->ps_flags & PMC_CC_F_USERSPACE) {
                                td = FIRST_THREAD_IN_PROC(po->po_owner);
                                addupc_intr(td, ps->ps_pc[0], 1);
                        }
                        goto entrydone;
                }

                /*
                 * Otherwise, this is either a sampling mode PMC that
                 * is attached to a different process than its owner,
                 * or a system-wide sampling PMC.  Dispatch a log
                 * entry to the PMC's owner process.
                 */
                pmclog_process_callchain(pm, ps);

        entrydone:
                ps->ps_nsamples = 0; /* mark entry as free */
                atomic_subtract_rel_int(&pm->pm_runcount, 1);

                /* increment read pointer, modulo sample size */
                if (++ps == psb->ps_fence)
                        psb->ps_read = psb->ps_samples;
                else
                        psb->ps_read = ps;
        }

        atomic_add_int(&pmc_stats.pm_log_sweeps, 1);

        /* Do not re-enable stalled PMCs if we failed to process any samples */
        if (n == 0)
                return;

        /*
         * Restart any stalled sampling PMCs on this CPU.
         *
         * If the NMI handler sets the pm_stalled field of a PMC after
         * the check below, we'll end up processing the stalled PMC at
         * the next hardclock tick.
         */
        for (n = 0; n < md->pmd_npmc; n++) {
                pcd = pmc_ri_to_classdep(md, n, &adjri);
                KASSERT(pcd != NULL,
                    ("[pmc,%d] null pcd ri=%d", __LINE__, n));
                (void) (*pcd->pcd_get_config)(cpu,adjri,&pm);

                if (pm == NULL ||                        /* !cfg'ed */
                    pm->pm_state != PMC_STATE_RUNNING || /* !active */
                    !PMC_IS_SAMPLING_MODE(PMC_TO_MODE(pm)) || /* !sampling */
                    !CPU_ISSET(cpu, &pm->pm_cpustate) || /* !desired */
                    !CPU_ISSET(cpu, &pm->pm_stalled)) /* !stalled */
                        continue;

                CPU_CLR_ATOMIC(cpu, &pm->pm_stalled);
                (*pcd->pcd_start_pmc)(cpu, adjri);
        }
}

/*
 * Event handlers.
 */

/*
 * Handle a process exit.
 *
 * Remove this process from all hash tables.  If this process
 * owned any PMCs, turn off those PMCs and deallocate them,
 * removing any associations with target processes.
 *
 * This function will be called by the last 'thread' of a
 * process.
 *
 * XXX This eventhandler gets called early in the exit process.
 * Consider using a 'hook' invocation from thread_exit() or equivalent
 * spot.  Another negative is that kse_exit doesn't seem to call
 * exit1() [??].
 *
 */

static void
pmc_process_exit(void *arg __unused, struct proc *p)
{
        struct pmc *pm;
        int adjri, cpu;
        unsigned int ri;
        int is_using_hwpmcs;
        struct pmc_owner *po;
        struct pmc_process *pp;
        struct pmc_classdep *pcd;
        pmc_value_t newvalue, tmp;

        PROC_LOCK(p);
        is_using_hwpmcs = p->p_flag & P_HWPMC;
        PROC_UNLOCK(p);

        /*
         * Log a sysexit event to all SS PMC owners.
         */
        LIST_FOREACH(po, &pmc_ss_owners, po_ssnext)
            if (po->po_flags & PMC_PO_OWNS_LOGFILE)
                    pmclog_process_sysexit(po, p->p_pid);

        if (!is_using_hwpmcs)
                return;

        PMC_GET_SX_XLOCK();
        PMCDBG3(PRC,EXT,1,"process-exit proc=%p (%d, %s)", p, p->p_pid,
            p->p_comm);

        /*
         * Since this code is invoked by the last thread in an exiting
         * process, we would have context switched IN at some prior
         * point.  However, with PREEMPTION, kernel mode context
         * switches may happen any time, so we want to disable a
         * context switch OUT till we get any PMCs targeting this
         * process off the hardware.
         *
         * We also need to atomically remove this process'
         * entry from our target process hash table, using
         * PMC_FLAG_REMOVE.
         */
        PMCDBG3(PRC,EXT,1, "process-exit proc=%p (%d, %s)", p, p->p_pid,
            p->p_comm);

        critical_enter(); /* no preemption */

        cpu = curthread->td_oncpu;

        if ((pp = pmc_find_process_descriptor(p,
                 PMC_FLAG_REMOVE)) != NULL) {

                PMCDBG2(PRC,EXT,2,
                    "process-exit proc=%p pmc-process=%p", p, pp);

                /*
                 * The exiting process could the target of
                 * some PMCs which will be running on
                 * currently executing CPU.
                 *
                 * We need to turn these PMCs off like we
                 * would do at context switch OUT time.
                 */
                for (ri = 0; ri < md->pmd_npmc; ri++) {

                        /*
                         * Pick up the pmc pointer from hardware
                         * state similar to the CSW_OUT code.
                         */
                        pm = NULL;

                        pcd = pmc_ri_to_classdep(md, ri, &adjri);

                        (void) (*pcd->pcd_get_config)(cpu, adjri, &pm);

                        PMCDBG2(PRC,EXT,2, "ri=%d pm=%p", ri, pm);

                        if (pm == NULL ||
                            !PMC_IS_VIRTUAL_MODE(PMC_TO_MODE(pm)))
                                continue;

                        PMCDBG4(PRC,EXT,2, "ppmcs[%d]=%p pm=%p "
                            "state=%d", ri, pp->pp_pmcs[ri].pp_pmc,
                            pm, pm->pm_state);

                        KASSERT(PMC_TO_ROWINDEX(pm) == ri,
                            ("[pmc,%d] ri mismatch pmc(%d) ri(%d)",
                                __LINE__, PMC_TO_ROWINDEX(pm), ri));

                        KASSERT(pm == pp->pp_pmcs[ri].pp_pmc,
                            ("[pmc,%d] pm %p != pp_pmcs[%d] %p",
                                __LINE__, pm, ri, pp->pp_pmcs[ri].pp_pmc));

                        KASSERT(pm->pm_runcount > 0,
                            ("[pmc,%d] bad runcount ri %d rc %d",
                                __LINE__, ri, pm->pm_runcount));

                        /*
                         * Change desired state, and then stop if not
                         * stalled. This two-step dance should avoid
                         * race conditions where an interrupt re-enables
                         * the PMC after this code has already checked
                         * the pm_stalled flag.
                         */
                        if (CPU_ISSET(cpu, &pm->pm_cpustate)) {
                                CPU_CLR_ATOMIC(cpu, &pm->pm_cpustate);
                                if (!CPU_ISSET(cpu, &pm->pm_stalled)) {
                                        (void) pcd->pcd_stop_pmc(cpu, adjri);
                                        pcd->pcd_read_pmc(cpu, adjri,
                                            &newvalue);
                                        tmp = newvalue -
                                            PMC_PCPU_SAVED(cpu,ri);

                                        mtx_pool_lock_spin(pmc_mtxpool, pm);
                                        pm->pm_gv.pm_savedvalue += tmp;
                                        pp->pp_pmcs[ri].pp_pmcval += tmp;
                                        mtx_pool_unlock_spin(pmc_mtxpool, pm);
                                }
                        }

                        atomic_subtract_rel_int(&pm->pm_runcount,1);

                        KASSERT((int) pm->pm_runcount >= 0,
                            ("[pmc,%d] runcount is %d", __LINE__, ri));

                        (void) pcd->pcd_config_pmc(cpu, adjri, NULL);
                }

                /*
                 * Inform the MD layer of this pseudo "context switch
                 * out"
                 */
                (void) md->pmd_switch_out(pmc_pcpu[cpu], pp);

                critical_exit(); /* ok to be pre-empted now */

                /*
                 * Unlink this process from the PMCs that are
                 * targeting it.  This will send a signal to
                 * all PMC owner's whose PMCs are orphaned.
                 *
                 * Log PMC value at exit time if requested.
                 */
                for (ri = 0; ri < md->pmd_npmc; ri++)
                        if ((pm = pp->pp_pmcs[ri].pp_pmc) != NULL) {
                                if (pm->pm_flags & PMC_F_NEEDS_LOGFILE &&
                                    PMC_IS_COUNTING_MODE(PMC_TO_MODE(pm)))
                                        pmclog_process_procexit(pm, pp);
                                pmc_unlink_target_process(pm, pp);
                        }
                free(pp, M_PMC);

        } else
                critical_exit(); /* pp == NULL */


        /*
         * If the process owned PMCs, free them up and free up
         * memory.
         */
        if ((po = pmc_find_owner_descriptor(p)) != NULL) {
                pmc_remove_owner(po);
                pmc_destroy_owner_descriptor(po);
        }

        sx_xunlock(&pmc_sx);
}

/*
 * Handle a process fork.
 *
 * If the parent process 'p1' is under HWPMC monitoring, then copy
 * over any attached PMCs that have 'do_descendants' semantics.
 */

static void
pmc_process_fork(void *arg __unused, struct proc *p1, struct proc *newproc,
    int flags)
{
        int is_using_hwpmcs;
        unsigned int ri;
        uint32_t do_descendants;
        struct pmc *pm;
        struct pmc_owner *po;
        struct pmc_process *ppnew, *ppold;

        (void) flags;           /* unused parameter */

        PROC_LOCK(p1);
        is_using_hwpmcs = p1->p_flag & P_HWPMC;
        PROC_UNLOCK(p1);

        /*
         * If there are system-wide sampling PMCs active, we need to
         * log all fork events to their owner's logs.
         */

        LIST_FOREACH(po, &pmc_ss_owners, po_ssnext)
            if (po->po_flags & PMC_PO_OWNS_LOGFILE)
                    pmclog_process_procfork(po, p1->p_pid, newproc->p_pid);

        if (!is_using_hwpmcs)
                return;

        PMC_GET_SX_XLOCK();
        PMCDBG4(PMC,FRK,1, "process-fork proc=%p (%d, %s) -> %p", p1,
            p1->p_pid, p1->p_comm, newproc);

        /*
         * If the parent process (curthread->td_proc) is a
         * target of any PMCs, look for PMCs that are to be
         * inherited, and link these into the new process
         * descriptor.
         */
        if ((ppold = pmc_find_process_descriptor(curthread->td_proc,
                 PMC_FLAG_NONE)) == NULL)
                goto done;              /* nothing to do */

        do_descendants = 0;
        for (ri = 0; ri < md->pmd_npmc; ri++)
                if ((pm = ppold->pp_pmcs[ri].pp_pmc) != NULL)
                        do_descendants |= pm->pm_flags & PMC_F_DESCENDANTS;
        if (do_descendants == 0) /* nothing to do */
                goto done;

        /* allocate a descriptor for the new process  */
        if ((ppnew = pmc_find_process_descriptor(newproc,
                 PMC_FLAG_ALLOCATE)) == NULL)
                goto done;

        /*
         * Run through all PMCs that were targeting the old process
         * and which specified F_DESCENDANTS and attach them to the
         * new process.
         *
         * Log the fork event to all owners of PMCs attached to this
         * process, if not already logged.
         */
        for (ri = 0; ri < md->pmd_npmc; ri++)
                if ((pm = ppold->pp_pmcs[ri].pp_pmc) != NULL &&
                    (pm->pm_flags & PMC_F_DESCENDANTS)) {
                        pmc_link_target_process(pm, ppnew);
                        po = pm->pm_owner;
                        if (po->po_sscount == 0 &&
                            po->po_flags & PMC_PO_OWNS_LOGFILE)
                                pmclog_process_procfork(po, p1->p_pid,
                                    newproc->p_pid);
                }

        /*
         * Now mark the new process as being tracked by this driver.
         */
        PROC_LOCK(newproc);
        newproc->p_flag |= P_HWPMC;
        PROC_UNLOCK(newproc);

 done:
        sx_xunlock(&pmc_sx);
}

static void
pmc_kld_load(void *arg __unused, linker_file_t lf)
{
        struct pmc_owner *po;

        sx_slock(&pmc_sx);

        /*
         * Notify owners of system sampling PMCs about KLD operations.
         */
        LIST_FOREACH(po, &pmc_ss_owners, po_ssnext)
                if (po->po_flags & PMC_PO_OWNS_LOGFILE)
                        pmclog_process_map_in(po, (pid_t) -1,
                            (uintfptr_t) lf->address, lf->filename);

        /*
         * TODO: Notify owners of (all) process-sampling PMCs too.
         */

        sx_sunlock(&pmc_sx);
}

static void
pmc_kld_unload(void *arg __unused, const char *filename __unused,
    caddr_t address, size_t size)
{
        struct pmc_owner *po;

        sx_slock(&pmc_sx);

        LIST_FOREACH(po, &pmc_ss_owners, po_ssnext)
                if (po->po_flags & PMC_PO_OWNS_LOGFILE)
                        pmclog_process_map_out(po, (pid_t) -1,
                            (uintfptr_t) address, (uintfptr_t) address + size);

        /*
         * TODO: Notify owners of process-sampling PMCs.
         */

        sx_sunlock(&pmc_sx);
}

/*
 * initialization
 */
static const char *
pmc_name_of_pmcclass(enum pmc_class class)
{

        switch (class) {
#undef  __PMC_CLASS
#define __PMC_CLASS(S,V,D)                                              \
        case PMC_CLASS_##S:                                             \
                return #S;
        __PMC_CLASSES();
        default:
                return ("<unknown>");
        }
}

/*
 * Base class initializer: allocate structure and set default classes.
 */
struct pmc_mdep *
pmc_mdep_alloc(int nclasses)
{
        struct pmc_mdep *md;
        int     n;

        /* SOFT + md classes */
        n = 1 + nclasses;
        md = malloc(sizeof(struct pmc_mdep) + n *
            sizeof(struct pmc_classdep), M_PMC, M_WAITOK|M_ZERO);
        md->pmd_nclass = n;

        /* Add base class. */
        pmc_soft_initialize(md);
        return md;
}

void
pmc_mdep_free(struct pmc_mdep *md)
{
        pmc_soft_finalize(md);
        free(md, M_PMC);
}

static int
generic_switch_in(struct pmc_cpu *pc, struct pmc_process *pp)
{
        (void) pc; (void) pp;

        return (0);
}

static int
generic_switch_out(struct pmc_cpu *pc, struct pmc_process *pp)
{
        (void) pc; (void) pp;

        return (0);
}

static struct pmc_mdep *
pmc_generic_cpu_initialize(void)
{
        struct pmc_mdep *md;

        md = pmc_mdep_alloc(0);

        md->pmd_cputype    = PMC_CPU_GENERIC;

        md->pmd_pcpu_init  = NULL;
        md->pmd_pcpu_fini  = NULL;
        md->pmd_switch_in  = generic_switch_in;
        md->pmd_switch_out = generic_switch_out;

        return (md);
}

static void
pmc_generic_cpu_finalize(struct pmc_mdep *md)
{
        (void) md;
}


static int
pmc_initialize(void)
{
        int c, cpu, error, n, ri;
        unsigned int maxcpu;
        struct pmc_binding pb;
        struct pmc_sample *ps;
        struct pmc_classdep *pcd;
        struct pmc_samplebuffer *sb;

        md = NULL;
        error = 0;

#ifdef  HWPMC_DEBUG
        /* parse debug flags first */
        if (TUNABLE_STR_FETCH(PMC_SYSCTL_NAME_PREFIX "debugflags",
                pmc_debugstr, sizeof(pmc_debugstr)))
                pmc_debugflags_parse(pmc_debugstr,
                    pmc_debugstr+strlen(pmc_debugstr));
#endif

        PMCDBG1(MOD,INI,0, "PMC Initialize (version %x)", PMC_VERSION);

        /* check kernel version */
        if (pmc_kernel_version != PMC_VERSION) {
                if (pmc_kernel_version == 0)
                        printf("hwpmc: this kernel has not been compiled with "
                            "'options HWPMC_HOOKS'.\n");
                else
                        printf("hwpmc: kernel version (0x%x) does not match "
                            "module version (0x%x).\n", pmc_kernel_version,
                            PMC_VERSION);
                return EPROGMISMATCH;
        }

        /*
         * check sysctl parameters
         */

        if (pmc_hashsize <= 0) {
                (void) printf("hwpmc: tunable \"hashsize\"=%d must be "
                    "greater than zero.\n", pmc_hashsize);
                pmc_hashsize = PMC_HASH_SIZE;
        }

        if (pmc_nsamples <= 0 || pmc_nsamples > 65535) {
                (void) printf("hwpmc: tunable \"nsamples\"=%d out of "
                    "range.\n", pmc_nsamples);
                pmc_nsamples = PMC_NSAMPLES;
        }

        if (pmc_callchaindepth <= 0 ||
            pmc_callchaindepth > PMC_CALLCHAIN_DEPTH_MAX) {
                (void) printf("hwpmc: tunable \"callchaindepth\"=%d out of "
                    "range - using %d.\n", pmc_callchaindepth,
                    PMC_CALLCHAIN_DEPTH_MAX);
                pmc_callchaindepth = PMC_CALLCHAIN_DEPTH_MAX;
        }

        md = pmc_md_initialize();
        if (md == NULL) {
                /* Default to generic CPU. */
                md = pmc_generic_cpu_initialize();
                if (md == NULL)
                        return (ENOSYS);
        }

        KASSERT(md->pmd_nclass >= 1 && md->pmd_npmc >= 1,
            ("[pmc,%d] no classes or pmcs", __LINE__));

        /* Compute the map from row-indices to classdep pointers. */
        pmc_rowindex_to_classdep = malloc(sizeof(struct pmc_classdep *) *
            md->pmd_npmc, M_PMC, M_WAITOK|M_ZERO);

        for (n = 0; n < md->pmd_npmc; n++)
                pmc_rowindex_to_classdep[n] = NULL;
        for (ri = c = 0; c < md->pmd_nclass; c++) {
                pcd = &md->pmd_classdep[c];
                for (n = 0; n < pcd->pcd_num; n++, ri++)
                        pmc_rowindex_to_classdep[ri] = pcd;
        }

        KASSERT(ri == md->pmd_npmc,
            ("[pmc,%d] npmc miscomputed: ri=%d, md->npmc=%d", __LINE__,
            ri, md->pmd_npmc));

        maxcpu = pmc_cpu_max();

        /* allocate space for the per-cpu array */
        pmc_pcpu = malloc(maxcpu * sizeof(struct pmc_cpu *), M_PMC,
            M_WAITOK|M_ZERO);

        /* per-cpu 'saved values' for managing process-mode PMCs */
        pmc_pcpu_saved = malloc(sizeof(pmc_value_t) * maxcpu * md->pmd_npmc,
            M_PMC, M_WAITOK);

        /* Perform CPU-dependent initialization. */
        pmc_save_cpu_binding(&pb);
        error = 0;
        for (cpu = 0; error == 0 && cpu < maxcpu; cpu++) {
                if (!pmc_cpu_is_active(cpu))
                        continue;
                pmc_select_cpu(cpu);
                pmc_pcpu[cpu] = malloc(sizeof(struct pmc_cpu) +
                    md->pmd_npmc * sizeof(struct pmc_hw *), M_PMC,
                    M_WAITOK|M_ZERO);
                if (md->pmd_pcpu_init)
                        error = md->pmd_pcpu_init(md, cpu);
                for (n = 0; error == 0 && n < md->pmd_nclass; n++)
                        error = md->pmd_classdep[n].pcd_pcpu_init(md, cpu);
        }
        pmc_restore_cpu_binding(&pb);

        if (error)
                return (error);

        /* allocate space for the sample array */
        for (cpu = 0; cpu < maxcpu; cpu++) {
                if (!pmc_cpu_is_active(cpu))
                        continue;

                sb = malloc(sizeof(struct pmc_samplebuffer) +
                    pmc_nsamples * sizeof(struct pmc_sample), M_PMC,
                    M_WAITOK|M_ZERO);
                sb->ps_read = sb->ps_write = sb->ps_samples;
                sb->ps_fence = sb->ps_samples + pmc_nsamples;

                KASSERT(pmc_pcpu[cpu] != NULL,
                    ("[pmc,%d] cpu=%d Null per-cpu data", __LINE__, cpu));

                sb->ps_callchains = malloc(pmc_callchaindepth * pmc_nsamples *
                    sizeof(uintptr_t), M_PMC, M_WAITOK|M_ZERO);

                for (n = 0, ps = sb->ps_samples; n < pmc_nsamples; n++, ps++)
                        ps->ps_pc = sb->ps_callchains +
                            (n * pmc_callchaindepth);

                pmc_pcpu[cpu]->pc_sb[PMC_HR] = sb;

                sb = malloc(sizeof(struct pmc_samplebuffer) +
                    pmc_nsamples * sizeof(struct pmc_sample), M_PMC,
                    M_WAITOK|M_ZERO);
                sb->ps_read = sb->ps_write = sb->ps_samples;
                sb->ps_fence = sb->ps_samples + pmc_nsamples;

                KASSERT(pmc_pcpu[cpu] != NULL,
                    ("[pmc,%d] cpu=%d Null per-cpu data", __LINE__, cpu));

                sb->ps_callchains = malloc(pmc_callchaindepth * pmc_nsamples *
                    sizeof(uintptr_t), M_PMC, M_WAITOK|M_ZERO);

                for (n = 0, ps = sb->ps_samples; n < pmc_nsamples; n++, ps++)
                        ps->ps_pc = sb->ps_callchains +
                            (n * pmc_callchaindepth);

                pmc_pcpu[cpu]->pc_sb[PMC_SR] = sb;
        }

        /* allocate space for the row disposition array */
        pmc_pmcdisp = malloc(sizeof(enum pmc_mode) * md->pmd_npmc,
            M_PMC, M_WAITOK|M_ZERO);

        /* mark all PMCs as available */
        for (n = 0; n < (int) md->pmd_npmc; n++)
                PMC_MARK_ROW_FREE(n);

        /* allocate thread hash tables */
        pmc_ownerhash = hashinit(pmc_hashsize, M_PMC,
            &pmc_ownerhashmask);

        pmc_processhash = hashinit(pmc_hashsize, M_PMC,
            &pmc_processhashmask);
        mtx_init(&pmc_processhash_mtx, "pmc-process-hash", "pmc-leaf",
            MTX_SPIN);

        LIST_INIT(&pmc_ss_owners);
        pmc_ss_count = 0;

        /* allocate a pool of spin mutexes */
        pmc_mtxpool = mtx_pool_create("pmc-leaf", pmc_mtxpool_size,
            MTX_SPIN);

        PMCDBG4(MOD,INI,1, "pmc_ownerhash=%p, mask=0x%lx "
            "targethash=%p mask=0x%lx", pmc_ownerhash, pmc_ownerhashmask,
            pmc_processhash, pmc_processhashmask);

        /* register process {exit,fork,exec} handlers */
        pmc_exit_tag = EVENTHANDLER_REGISTER(process_exit,
            pmc_process_exit, NULL, EVENTHANDLER_PRI_ANY);
        pmc_fork_tag = EVENTHANDLER_REGISTER(process_fork,
            pmc_process_fork, NULL, EVENTHANDLER_PRI_ANY);

        /* register kld event handlers */
        pmc_kld_load_tag = EVENTHANDLER_REGISTER(kld_load, pmc_kld_load,
            NULL, EVENTHANDLER_PRI_ANY);
        pmc_kld_unload_tag = EVENTHANDLER_REGISTER(kld_unload, pmc_kld_unload,
            NULL, EVENTHANDLER_PRI_ANY);

        /* initialize logging */
        pmclog_initialize();

        /* set hook functions */
        pmc_intr = md->pmd_intr;
        pmc_hook = pmc_hook_handler;

        if (error == 0) {
                printf(PMC_MODULE_NAME ":");
                for (n = 0; n < (int) md->pmd_nclass; n++) {
                        pcd = &md->pmd_classdep[n];
                        printf(" %s/%d/%d/0x%b",
                            pmc_name_of_pmcclass(pcd->pcd_class),
                            pcd->pcd_num,
                            pcd->pcd_width,
                            pcd->pcd_caps,
                            "\20"
                            "\1INT\2USR\3SYS\4EDG\5THR"
                            "\6REA\7WRI\10INV\11QUA\12PRC"
                            "\13TAG\14CSC");
                }
                printf("\n");
        }

        return (error);
}

/* prepare to be unloaded */
static void
pmc_cleanup(void)
{
        int c, cpu;
        unsigned int maxcpu;
        struct pmc_ownerhash *ph;
        struct pmc_owner *po, *tmp;
        struct pmc_binding pb;
#ifdef  HWPMC_DEBUG
        struct pmc_processhash *prh;
#endif

        PMCDBG0(MOD,INI,0, "cleanup");

        /* switch off sampling */
        CPU_ZERO(&pmc_cpumask);
        pmc_intr = NULL;

        sx_xlock(&pmc_sx);
        if (pmc_hook == NULL) { /* being unloaded already */
                sx_xunlock(&pmc_sx);
                return;
        }

        pmc_hook = NULL; /* prevent new threads from entering module */

        /* deregister event handlers */
        EVENTHANDLER_DEREGISTER(process_fork, pmc_fork_tag);
        EVENTHANDLER_DEREGISTER(process_exit, pmc_exit_tag);
        EVENTHANDLER_DEREGISTER(kld_load, pmc_kld_load_tag);
        EVENTHANDLER_DEREGISTER(kld_unload, pmc_kld_unload_tag);

        /* send SIGBUS to all owner threads, free up allocations */
        if (pmc_ownerhash)
                for (ph = pmc_ownerhash;
                     ph <= &pmc_ownerhash[pmc_ownerhashmask];
                     ph++) {
                        LIST_FOREACH_SAFE(po, ph, po_next, tmp) {
                                pmc_remove_owner(po);

                                /* send SIGBUS to owner processes */
                                PMCDBG3(MOD,INI,2, "cleanup signal proc=%p "
                                    "(%d, %s)", po->po_owner,
                                    po->po_owner->p_pid,
                                    po->po_owner->p_comm);

                                PROC_LOCK(po->po_owner);
                                kern_psignal(po->po_owner, SIGBUS);
                                PROC_UNLOCK(po->po_owner);

                                pmc_destroy_owner_descriptor(po);
                        }
                }

        /* reclaim allocated data structures */
        if (pmc_mtxpool)
                mtx_pool_destroy(&pmc_mtxpool);

        mtx_destroy(&pmc_processhash_mtx);
        if (pmc_processhash) {
#ifdef  HWPMC_DEBUG
                struct pmc_process *pp;

                PMCDBG0(MOD,INI,3, "destroy process hash");
                for (prh = pmc_processhash;
                     prh <= &pmc_processhash[pmc_processhashmask];
                     prh++)
                        LIST_FOREACH(pp, prh, pp_next)
                            PMCDBG1(MOD,INI,3, "pid=%d", pp->pp_proc->p_pid);
#endif

                hashdestroy(pmc_processhash, M_PMC, pmc_processhashmask);
                pmc_processhash = NULL;
        }

        if (pmc_ownerhash) {
                PMCDBG0(MOD,INI,3, "destroy owner hash");
                hashdestroy(pmc_ownerhash, M_PMC, pmc_ownerhashmask);
                pmc_ownerhash = NULL;
        }

        KASSERT(LIST_EMPTY(&pmc_ss_owners),
            ("[pmc,%d] Global SS owner list not empty", __LINE__));
        KASSERT(pmc_ss_count == 0,
            ("[pmc,%d] Global SS count not empty", __LINE__));

        /* do processor and pmc-class dependent cleanup */
        maxcpu = pmc_cpu_max();

        PMCDBG0(MOD,INI,3, "md cleanup");
        if (md) {
                pmc_save_cpu_binding(&pb);
                for (cpu = 0; cpu < maxcpu; cpu++) {
                        PMCDBG2(MOD,INI,1,"pmc-cleanup cpu=%d pcs=%p",
                            cpu, pmc_pcpu[cpu]);
                        if (!pmc_cpu_is_active(cpu) || pmc_pcpu[cpu] == NULL)
                                continue;
                        pmc_select_cpu(cpu);
                        for (c = 0; c < md->pmd_nclass; c++)
                                md->pmd_classdep[c].pcd_pcpu_fini(md, cpu);
                        if (md->pmd_pcpu_fini)
                                md->pmd_pcpu_fini(md, cpu);
                }

                if (md->pmd_cputype == PMC_CPU_GENERIC)
                        pmc_generic_cpu_finalize(md);
                else
                        pmc_md_finalize(md);

                pmc_mdep_free(md);
                md = NULL;
                pmc_restore_cpu_binding(&pb);
        }

        /* Free per-cpu descriptors. */
        for (cpu = 0; cpu < maxcpu; cpu++) {
                if (!pmc_cpu_is_active(cpu))
                        continue;
                KASSERT(pmc_pcpu[cpu]->pc_sb[PMC_HR] != NULL,
                    ("[pmc,%d] Null hw cpu sample buffer cpu=%d", __LINE__,
                        cpu));
                KASSERT(pmc_pcpu[cpu]->pc_sb[PMC_SR] != NULL,
                    ("[pmc,%d] Null sw cpu sample buffer cpu=%d", __LINE__,
                        cpu));
                free(pmc_pcpu[cpu]->pc_sb[PMC_HR]->ps_callchains, M_PMC);
                free(pmc_pcpu[cpu]->pc_sb[PMC_HR], M_PMC);
                free(pmc_pcpu[cpu]->pc_sb[PMC_SR]->ps_callchains, M_PMC);
                free(pmc_pcpu[cpu]->pc_sb[PMC_SR], M_PMC);
                free(pmc_pcpu[cpu], M_PMC);
        }

        free(pmc_pcpu, M_PMC);
        pmc_pcpu = NULL;

        free(pmc_pcpu_saved, M_PMC);
        pmc_pcpu_saved = NULL;

        if (pmc_pmcdisp) {
                free(pmc_pmcdisp, M_PMC);
                pmc_pmcdisp = NULL;
        }

        if (pmc_rowindex_to_classdep) {
                free(pmc_rowindex_to_classdep, M_PMC);
                pmc_rowindex_to_classdep = NULL;
        }

        pmclog_shutdown();

        sx_xunlock(&pmc_sx);    /* we are done */
}

/*
 * The function called at load/unload.
 */

static int
load (struct module *module __unused, int cmd, void *arg __unused)
{
        int error;

        error = 0;

        switch (cmd) {
        case MOD_LOAD :
                /* initialize the subsystem */
                error = pmc_initialize();
                if (error != 0)
                        break;
                PMCDBG2(MOD,INI,1, "syscall=%d maxcpu=%d",
                    pmc_syscall_num, pmc_cpu_max());
                break;


        case MOD_UNLOAD :
        case MOD_SHUTDOWN:
                pmc_cleanup();
                PMCDBG0(MOD,INI,1, "unloaded");
                break;

        default :
                error = EINVAL; /* XXX should panic(9) */
                break;
        }

        return error;
}

/* memory pool */
MALLOC_DEFINE(M_PMC, "pmc", "Memory space for the PMC module");