sys/vm/vm_fault.c

   1 /*-
   2  * SPDX-License-Identifier: (BSD-4-Clause AND MIT-CMU)
   3  *
   4  * Copyright (c) 1991, 1993
   5  *      The Regents of the University of California.  All rights reserved.
   6  * Copyright (c) 1994 John S. Dyson
   7  * All rights reserved.
   8  * Copyright (c) 1994 David Greenman
   9  * All rights reserved.
  10  *
  11  *
  12  * This code is derived from software contributed to Berkeley by
  13  * The Mach Operating System project at Carnegie-Mellon University.
  14  *
  15  * Redistribution and use in source and binary forms, with or without
  16  * modification, are permitted provided that the following conditions
  17  * are met:
  18  * 1. Redistributions of source code must retain the above copyright
  19  *    notice, this list of conditions and the following disclaimer.
  20  * 2. Redistributions in binary form must reproduce the above copyright
  21  *    notice, this list of conditions and the following disclaimer in the
  22  *    documentation and/or other materials provided with the distribution.
  23  * 3. All advertising materials mentioning features or use of this software
  24  *    must display the following acknowledgement:
  25  *      This product includes software developed by the University of
  26  *      California, Berkeley and its contributors.
  27  * 4. Neither the name of the University nor the names of its contributors
  28  *    may be used to endorse or promote products derived from this software
  29  *    without specific prior written permission.
  30  *
  31  * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
  32  * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
  33  * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
  34  * ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
  35  * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
  36  * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
  37  * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
  38  * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
  39  * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
  40  * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
  41  * SUCH DAMAGE.
  42  *
  43  *      from: @(#)vm_fault.c    8.4 (Berkeley) 1/12/94
  44  *
  45  *
  46  * Copyright (c) 1987, 1990 Carnegie-Mellon University.
  47  * All rights reserved.
  48  *
  49  * Authors: Avadis Tevanian, Jr., Michael Wayne Young
  50  *
  51  * Permission to use, copy, modify and distribute this software and
  52  * its documentation is hereby granted, provided that both the copyright
  53  * notice and this permission notice appear in all copies of the
  54  * software, derivative works or modified versions, and any portions
  55  * thereof, and that both notices appear in supporting documentation.
  56  *
  57  * CARNEGIE MELLON ALLOWS FREE USE OF THIS SOFTWARE IN ITS "AS IS"
  58  * CONDITION.  CARNEGIE MELLON DISCLAIMS ANY LIABILITY OF ANY KIND
  59  * FOR ANY DAMAGES WHATSOEVER RESULTING FROM THE USE OF THIS SOFTWARE.
  60  *
  61  * Carnegie Mellon requests users of this software to return to
  62  *
  63  *  Software Distribution Coordinator  or  Software.Distribution@CS.CMU.EDU
  64  *  School of Computer Science
  65  *  Carnegie Mellon University
  66  *  Pittsburgh PA 15213-3890
  67  *
  68  * any improvements or extensions that they make and grant Carnegie the
  69  * rights to redistribute these changes.
  70  */
  71
  72 /*
  73  *      Page fault handling module.
  74  */
  75
  76 #include <sys/cdefs.h>
  77 __FBSDID("$FreeBSD$");
  78
  79 #include "opt_ktrace.h"
  80 #include "opt_vm.h"
  81
  82 #include <sys/param.h>
  83 #include <sys/systm.h>
  84 #include <sys/kernel.h>
  85 #include <sys/lock.h>
  86 #include <sys/mman.h>
  87 #include <sys/proc.h>
  88 #include <sys/racct.h>
  89 #include <sys/resourcevar.h>
  90 #include <sys/rwlock.h>
  91 #include <sys/sysctl.h>
  92 #include <sys/vmmeter.h>
  93 #include <sys/vnode.h>
  94 #ifdef KTRACE
  95 #include <sys/ktrace.h>
  96 #endif
  97
  98 #include <vm/vm.h>
  99 #include <vm/vm_param.h>
 100 #include <vm/pmap.h>
 101 #include <vm/vm_map.h>
 102 #include <vm/vm_object.h>
 103 #include <vm/vm_page.h>
 104 #include <vm/vm_pageout.h>
 105 #include <vm/vm_kern.h>
 106 #include <vm/vm_pager.h>
 107 #include <vm/vm_extern.h>
 108 #include <vm/vm_reserv.h>
 109
 110 #define PFBAK 4
 111 #define PFFOR 4
 112
 113 #define VM_FAULT_READ_DEFAULT   (1 + VM_FAULT_READ_AHEAD_INIT)
 114 #define VM_FAULT_READ_MAX       (1 + VM_FAULT_READ_AHEAD_MAX)
 115
 116 #define VM_FAULT_DONTNEED_MIN   1048576
 117
 118 struct faultstate {
 119         vm_page_t m;
 120         vm_object_t object;
 121         vm_pindex_t pindex;
 122         vm_page_t first_m;
 123         vm_object_t     first_object;
 124         vm_pindex_t first_pindex;
 125         vm_map_t map;
 126         vm_map_entry_t entry;
 127         int map_generation;
 128         bool lookup_still_valid;
 129         struct vnode *vp;
 130 };
 131
 132 static void vm_fault_dontneed(const struct faultstate *fs, vm_offset_t vaddr,
 133             int ahead);
 134 static void vm_fault_prefault(const struct faultstate *fs, vm_offset_t addra,
 135             int backward, int forward, bool obj_locked);
 136
 137 static inline void
 138 release_page(struct faultstate *fs)
 139 {
 140
 141         vm_page_xunbusy(fs->m);
 142         vm_page_lock(fs->m);
 143         vm_page_deactivate(fs->m);
 144         vm_page_unlock(fs->m);
 145         fs->m = NULL;
 146 }
 147
 148 static inline void
 149 unlock_map(struct faultstate *fs)
 150 {
 151
 152         if (fs->lookup_still_valid) {
 153                 vm_map_lookup_done(fs->map, fs->entry);
 154                 fs->lookup_still_valid = false;
 155         }
 156 }
 157
 158 static void
 159 unlock_vp(struct faultstate *fs)
 160 {
 161
 162         if (fs->vp != NULL) {
 163                 vput(fs->vp);
 164                 fs->vp = NULL;
 165         }
 166 }
 167
 168 static void
 169 unlock_and_deallocate(struct faultstate *fs)
 170 {
 171
 172         vm_object_pip_wakeup(fs->object);
 173         VM_OBJECT_WUNLOCK(fs->object);
 174         if (fs->object != fs->first_object) {
 175                 VM_OBJECT_WLOCK(fs->first_object);
 176                 vm_page_lock(fs->first_m);
 177                 vm_page_free(fs->first_m);
 178                 vm_page_unlock(fs->first_m);
 179                 vm_object_pip_wakeup(fs->first_object);
 180                 VM_OBJECT_WUNLOCK(fs->first_object);
 181                 fs->first_m = NULL;
 182         }
 183         vm_object_deallocate(fs->first_object);
 184         unlock_map(fs);
 185         unlock_vp(fs);
 186 }
 187
 188 static void
 189 vm_fault_dirty(vm_map_entry_t entry, vm_page_t m, vm_prot_t prot,
 190     vm_prot_t fault_type, int fault_flags, bool set_wd)
 191 {
 192         bool need_dirty;
 193
 194         if (((prot & VM_PROT_WRITE) == 0 &&
 195             (fault_flags & VM_FAULT_DIRTY) == 0) ||
 196             (m->oflags & VPO_UNMANAGED) != 0)
 197                 return;
 198
 199         VM_OBJECT_ASSERT_LOCKED(m->object);
 200
 201         need_dirty = ((fault_type & VM_PROT_WRITE) != 0 &&
 202             (fault_flags & VM_FAULT_WIRE) == 0) ||
 203             (fault_flags & VM_FAULT_DIRTY) != 0;
 204
 205         if (set_wd)
 206                 vm_object_set_writeable_dirty(m->object);
 207         else
 208                 /*
 209                  * If two callers of vm_fault_dirty() with set_wd ==
 210                  * FALSE, one for the map entry with MAP_ENTRY_NOSYNC
 211                  * flag set, other with flag clear, race, it is
 212                  * possible for the no-NOSYNC thread to see m->dirty
 213                  * != 0 and not clear VPO_NOSYNC.  Take vm_page lock
 214                  * around manipulation of VPO_NOSYNC and
 215                  * vm_page_dirty() call, to avoid the race and keep
 216                  * m->oflags consistent.
 217                  */
 218                 vm_page_lock(m);
 219
 220         /*
 221          * If this is a NOSYNC mmap we do not want to set VPO_NOSYNC
 222          * if the page is already dirty to prevent data written with
 223          * the expectation of being synced from not being synced.
 224          * Likewise if this entry does not request NOSYNC then make
 225          * sure the page isn't marked NOSYNC.  Applications sharing
 226          * data should use the same flags to avoid ping ponging.
 227          */
 228         if ((entry->eflags & MAP_ENTRY_NOSYNC) != 0) {
 229                 if (m->dirty == 0) {
 230                         m->oflags |= VPO_NOSYNC;
 231                 }
 232         } else {
 233                 m->oflags &= ~VPO_NOSYNC;
 234         }
 235
 236         /*
 237          * If the fault is a write, we know that this page is being
 238          * written NOW so dirty it explicitly to save on
 239          * pmap_is_modified() calls later.
 240          *
 241          * Also, since the page is now dirty, we can possibly tell
 242          * the pager to release any swap backing the page.  Calling
 243          * the pager requires a write lock on the object.
 244          */
 245         if (need_dirty)
 246                 vm_page_dirty(m);
 247         if (!set_wd)
 248                 vm_page_unlock(m);
 249         else if (need_dirty)
 250                 vm_pager_page_unswapped(m);
 251 }
 252
 253 static void
 254 vm_fault_fill_hold(vm_page_t *m_hold, vm_page_t m)
 255 {
 256
 257         if (m_hold != NULL) {
 258                 *m_hold = m;
 259                 vm_page_lock(m);
 260                 vm_page_hold(m);
 261                 vm_page_unlock(m);
 262         }
 263 }
 264
 265 /*
 266  * Unlocks fs.first_object and fs.map on success.
 267  */
 268 static int
 269 vm_fault_soft_fast(struct faultstate *fs, vm_offset_t vaddr, vm_prot_t prot,
 270     int fault_type, int fault_flags, boolean_t wired, vm_page_t *m_hold)
 271 {
 272         vm_page_t m, m_map;
 273 #if (defined(__amd64__) || defined(__i386__) || defined(__aarch64__)) && \
 274     VM_NRESERVLEVEL > 0
 275         vm_page_t m_super;
 276         int flags;
 277 #endif
 278         int psind, rv;
 279
 280         MPASS(fs->vp == NULL);
 281         m = vm_page_lookup(fs->first_object, fs->first_pindex);
 282         /* A busy page can be mapped for read|execute access. */
 283         if (m == NULL || ((prot & VM_PROT_WRITE) != 0 &&
 284             vm_page_busied(m)) || m->valid != VM_PAGE_BITS_ALL)
 285                 return (KERN_FAILURE);
 286         m_map = m;
 287         psind = 0;
 288 #if (defined(__amd64__) || defined(__i386__) || defined(__aarch64__)) && \
 289     VM_NRESERVLEVEL > 0
 290         if ((m->flags & PG_FICTITIOUS) == 0 &&
 291             (m_super = vm_reserv_to_superpage(m)) != NULL &&
 292             rounddown2(vaddr, pagesizes[m_super->psind]) >= fs->entry->start &&
 293             roundup2(vaddr + 1, pagesizes[m_super->psind]) <= fs->entry->end &&
 294             (vaddr & (pagesizes[m_super->psind] - 1)) == (VM_PAGE_TO_PHYS(m) &
 295             (pagesizes[m_super->psind] - 1)) &&
 296             pmap_ps_enabled(fs->map->pmap)) {
 297                 flags = PS_ALL_VALID;
 298                 if ((prot & VM_PROT_WRITE) != 0) {
 299                         /*
 300                          * Create a superpage mapping allowing write access
 301                          * only if none of the constituent pages are busy and
 302                          * all of them are already dirty (except possibly for
 303                          * the page that was faulted on).
 304                          */
 305                         flags |= PS_NONE_BUSY;
 306                         if ((fs->first_object->flags & OBJ_UNMANAGED) == 0)
 307                                 flags |= PS_ALL_DIRTY;
 308                 }
 309                 if (vm_page_ps_test(m_super, flags, m)) {
 310                         m_map = m_super;
 311                         psind = m_super->psind;
 312                         vaddr = rounddown2(vaddr, pagesizes[psind]);
 313                         /* Preset the modified bit for dirty superpages. */
 314                         if ((flags & PS_ALL_DIRTY) != 0)
 315                                 fault_type |= VM_PROT_WRITE;
 316                 }
 317         }
 318 #endif
 319         rv = pmap_enter(fs->map->pmap, vaddr, m_map, prot, fault_type |
 320             PMAP_ENTER_NOSLEEP | (wired ? PMAP_ENTER_WIRED : 0), psind);
 321         if (rv != KERN_SUCCESS)
 322                 return (rv);
 323         vm_fault_fill_hold(m_hold, m);
 324         vm_fault_dirty(fs->entry, m, prot, fault_type, fault_flags, false);
 325         if (psind == 0 && !wired)
 326                 vm_fault_prefault(fs, vaddr, PFBAK, PFFOR, true);
 327         VM_OBJECT_RUNLOCK(fs->first_object);
 328         vm_map_lookup_done(fs->map, fs->entry);
 329         curthread->td_ru.ru_minflt++;
 330         return (KERN_SUCCESS);
 331 }
 332
 333 static void
 334 vm_fault_restore_map_lock(struct faultstate *fs)
 335 {
 336
 337         VM_OBJECT_ASSERT_WLOCKED(fs->first_object);
 338         MPASS(fs->first_object->paging_in_progress > 0);
 339
 340         if (!vm_map_trylock_read(fs->map)) {
 341                 VM_OBJECT_WUNLOCK(fs->first_object);
 342                 vm_map_lock_read(fs->map);
 343                 VM_OBJECT_WLOCK(fs->first_object);
 344         }
 345         fs->lookup_still_valid = true;
 346 }
 347
 348 static void
 349 vm_fault_populate_check_page(vm_page_t m)
 350 {
 351
 352         /*
 353          * Check each page to ensure that the pager is obeying the
 354          * interface: the page must be installed in the object, fully
 355          * valid, and exclusively busied.
 356          */
 357         MPASS(m != NULL);
 358         MPASS(m->valid == VM_PAGE_BITS_ALL);
 359         MPASS(vm_page_xbusied(m));
 360 }
 361
 362 static void
 363 vm_fault_populate_cleanup(vm_object_t object, vm_pindex_t first,
 364     vm_pindex_t last)
 365 {
 366         vm_page_t m;
 367         vm_pindex_t pidx;
 368
 369         VM_OBJECT_ASSERT_WLOCKED(object);
 370         MPASS(first <= last);
 371         for (pidx = first, m = vm_page_lookup(object, pidx);
 372             pidx <= last; pidx++, m = vm_page_next(m)) {
 373                 vm_fault_populate_check_page(m);
 374                 vm_page_lock(m);
 375                 vm_page_deactivate(m);
 376                 vm_page_unlock(m);
 377                 vm_page_xunbusy(m);
 378         }
 379 }
 380
 381 static int
 382 vm_fault_populate(struct faultstate *fs, vm_prot_t prot, int fault_type,
 383     int fault_flags, boolean_t wired, vm_page_t *m_hold)
 384 {
 385         struct mtx *m_mtx;
 386         vm_offset_t vaddr;
 387         vm_page_t m;
 388         vm_pindex_t map_first, map_last, pager_first, pager_last, pidx;
 389         int i, npages, psind, rv;
 390
 391         MPASS(fs->object == fs->first_object);
 392         VM_OBJECT_ASSERT_WLOCKED(fs->first_object);
 393         MPASS(fs->first_object->paging_in_progress > 0);
 394         MPASS(fs->first_object->backing_object == NULL);
 395         MPASS(fs->lookup_still_valid);
 396
 397         pager_first = OFF_TO_IDX(fs->entry->offset);
 398         pager_last = pager_first + atop(fs->entry->end - fs->entry->start) - 1;
 399         unlock_map(fs);
 400         unlock_vp(fs);
 401
 402         /*
 403          * Call the pager (driver) populate() method.
 404          *
 405          * There is no guarantee that the method will be called again
 406          * if the current fault is for read, and a future fault is
 407          * for write.  Report the entry's maximum allowed protection
 408          * to the driver.
 409          */
 410         rv = vm_pager_populate(fs->first_object, fs->first_pindex,
 411             fault_type, fs->entry->max_protection, &pager_first, &pager_last);
 412
 413         VM_OBJECT_ASSERT_WLOCKED(fs->first_object);
 414         if (rv == VM_PAGER_BAD) {
 415                 /*
 416                  * VM_PAGER_BAD is the backdoor for a pager to request
 417                  * normal fault handling.
 418                  */
 419                 vm_fault_restore_map_lock(fs);
 420                 if (fs->map->timestamp != fs->map_generation)
 421                         return (KERN_RESOURCE_SHORTAGE); /* RetryFault */
 422                 return (KERN_NOT_RECEIVER);
 423         }
 424         if (rv != VM_PAGER_OK)
 425                 return (KERN_FAILURE); /* AKA SIGSEGV */
 426
 427         /* Ensure that the driver is obeying the interface. */
 428         MPASS(pager_first <= pager_last);
 429         MPASS(fs->first_pindex <= pager_last);
 430         MPASS(fs->first_pindex >= pager_first);
 431         MPASS(pager_last < fs->first_object->size);
 432
 433         vm_fault_restore_map_lock(fs);
 434         if (fs->map->timestamp != fs->map_generation) {
 435                 vm_fault_populate_cleanup(fs->first_object, pager_first,
 436                     pager_last);
 437                 return (KERN_RESOURCE_SHORTAGE); /* RetryFault */
 438         }
 439
 440         /*
 441          * The map is unchanged after our last unlock.  Process the fault.
 442          *
 443          * The range [pager_first, pager_last] that is given to the
 444          * pager is only a hint.  The pager may populate any range
 445          * within the object that includes the requested page index.
 446          * In case the pager expanded the range, clip it to fit into
 447          * the map entry.
 448          */
 449         map_first = OFF_TO_IDX(fs->entry->offset);
 450         if (map_first > pager_first) {
 451                 vm_fault_populate_cleanup(fs->first_object, pager_first,
 452                     map_first - 1);
 453                 pager_first = map_first;
 454         }
 455         map_last = map_first + atop(fs->entry->end - fs->entry->start) - 1;
 456         if (map_last < pager_last) {
 457                 vm_fault_populate_cleanup(fs->first_object, map_last + 1,
 458                     pager_last);
 459                 pager_last = map_last;
 460         }
 461         for (pidx = pager_first, m = vm_page_lookup(fs->first_object, pidx);
 462             pidx <= pager_last;
 463             pidx += npages, m = vm_page_next(&m[npages - 1])) {
 464                 vaddr = fs->entry->start + IDX_TO_OFF(pidx) - fs->entry->offset;
 465 #if defined(__amd64__) || defined(__i386__) || defined(__aarch64__)
 466                 psind = m->psind;
 467                 if (psind > 0 && ((vaddr & (pagesizes[psind] - 1)) != 0 ||
 468                     pidx + OFF_TO_IDX(pagesizes[psind]) - 1 > pager_last ||
 469                     !pmap_ps_enabled(fs->map->pmap)))
 470                         psind = 0;
 471 #else
 472                 psind = 0;
 473 #endif
 474                 npages = atop(pagesizes[psind]);
 475                 for (i = 0; i < npages; i++) {
 476                         vm_fault_populate_check_page(&m[i]);
 477                         vm_fault_dirty(fs->entry, &m[i], prot, fault_type,
 478                             fault_flags, true);
 479                 }
 480                 VM_OBJECT_WUNLOCK(fs->first_object);
 481                 pmap_enter(fs->map->pmap, vaddr, m, prot, fault_type | (wired ?
 482                     PMAP_ENTER_WIRED : 0), psind);
 483                 VM_OBJECT_WLOCK(fs->first_object);
 484                 m_mtx = NULL;
 485                 for (i = 0; i < npages; i++) {
 486                         vm_page_change_lock(&m[i], &m_mtx);
 487                         if ((fault_flags & VM_FAULT_WIRE) != 0)
 488                                 vm_page_wire(&m[i]);
 489                         else
 490                                 vm_page_activate(&m[i]);
 491                         if (m_hold != NULL && m[i].pindex == fs->first_pindex) {
 492                                 *m_hold = &m[i];
 493                                 vm_page_hold(&m[i]);
 494                         }
 495                         vm_page_xunbusy_maybelocked(&m[i]);
 496                 }
 497                 if (m_mtx != NULL)
 498                         mtx_unlock(m_mtx);
 499         }
 500         curthread->td_ru.ru_majflt++;
 501         return (KERN_SUCCESS);
 502 }
 503
 504 /*
 505  *      vm_fault:
 506  *
 507  *      Handle a page fault occurring at the given address,
 508  *      requiring the given permissions, in the map specified.
 509  *      If successful, the page is inserted into the
 510  *      associated physical map.
 511  *
 512  *      NOTE: the given address should be truncated to the
 513  *      proper page address.
 514  *
 515  *      KERN_SUCCESS is returned if the page fault is handled; otherwise,
 516  *      a standard error specifying why the fault is fatal is returned.
 517  *
 518  *      The map in question must be referenced, and remains so.
 519  *      Caller may hold no locks.
 520  */
 521 int
 522 vm_fault(vm_map_t map, vm_offset_t vaddr, vm_prot_t fault_type,
 523     int fault_flags)
 524 {
 525         struct thread *td;
 526         int result;
 527
 528         td = curthread;
 529         if ((td->td_pflags & TDP_NOFAULTING) != 0)
 530                 return (KERN_PROTECTION_FAILURE);
 531 #ifdef KTRACE
 532         if (map != kernel_map && KTRPOINT(td, KTR_FAULT))
 533                 ktrfault(vaddr, fault_type);
 534 #endif
 535         result = vm_fault_hold(map, trunc_page(vaddr), fault_type, fault_flags,
 536             NULL);
 537 #ifdef KTRACE
 538         if (map != kernel_map && KTRPOINT(td, KTR_FAULTEND))
 539                 ktrfaultend(result);
 540 #endif
 541         return (result);
 542 }
 543
 544 int
 545 vm_fault_hold(vm_map_t map, vm_offset_t vaddr, vm_prot_t fault_type,
 546     int fault_flags, vm_page_t *m_hold)
 547 {
 548         struct faultstate fs;
 549         struct vnode *vp;
 550         vm_object_t next_object, retry_object;
 551         vm_offset_t e_end, e_start;
 552         vm_pindex_t retry_pindex;
 553         vm_prot_t prot, retry_prot;
 554         int ahead, alloc_req, behind, cluster_offset, error, era, faultcount;
 555         int locked, nera, result, rv;
 556         u_char behavior;
 557         boolean_t wired;        /* Passed by reference. */
 558         bool dead, hardfault, is_first_object_locked;
 559
 560         VM_CNT_INC(v_vm_faults);
 561         fs.vp = NULL;
 562         faultcount = 0;
 563         nera = -1;
 564         hardfault = false;
 565
 566 RetryFault:;
 567
 568         /*
 569          * Find the backing store object and offset into it to begin the
 570          * search.
 571          */
 572         fs.map = map;
 573         result = vm_map_lookup(&fs.map, vaddr, fault_type |
 574             VM_PROT_FAULT_LOOKUP, &fs.entry, &fs.first_object,
 575             &fs.first_pindex, &prot, &wired);
 576         if (result != KERN_SUCCESS) {
 577                 unlock_vp(&fs);
 578                 return (result);
 579         }
 580
 581         fs.map_generation = fs.map->timestamp;
 582
 583         if (fs.entry->eflags & MAP_ENTRY_NOFAULT) {
 584                 panic("%s: fault on nofault entry, addr: %#lx",
 585                     __func__, (u_long)vaddr);
 586         }
 587
 588         if (fs.entry->eflags & MAP_ENTRY_IN_TRANSITION &&
 589             fs.entry->wiring_thread != curthread) {
 590                 vm_map_unlock_read(fs.map);
 591                 vm_map_lock(fs.map);
 592                 if (vm_map_lookup_entry(fs.map, vaddr, &fs.entry) &&
 593                     (fs.entry->eflags & MAP_ENTRY_IN_TRANSITION)) {
 594                         unlock_vp(&fs);
 595                         fs.entry->eflags |= MAP_ENTRY_NEEDS_WAKEUP;
 596                         vm_map_unlock_and_wait(fs.map, 0);
 597                 } else
 598                         vm_map_unlock(fs.map);
 599                 goto RetryFault;
 600         }
 601
 602         MPASS((fs.entry->eflags & MAP_ENTRY_GUARD) == 0);
 603
 604         if (wired)
 605                 fault_type = prot | (fault_type & VM_PROT_COPY);
 606         else
 607                 KASSERT((fault_flags & VM_FAULT_WIRE) == 0,
 608                     ("!wired && VM_FAULT_WIRE"));
 609
 610         /*
 611          * Try to avoid lock contention on the top-level object through
 612          * special-case handling of some types of page faults, specifically,
 613          * those that are both (1) mapping an existing page from the top-
 614          * level object and (2) not having to mark that object as containing
 615          * dirty pages.  Under these conditions, a read lock on the top-level
 616          * object suffices, allowing multiple page faults of a similar type to
 617          * run in parallel on the same top-level object.
 618          */
 619         if (fs.vp == NULL /* avoid locked vnode leak */ &&
 620             (fault_flags & (VM_FAULT_WIRE | VM_FAULT_DIRTY)) == 0 &&
 621             /* avoid calling vm_object_set_writeable_dirty() */
 622             ((prot & VM_PROT_WRITE) == 0 ||
 623             (fs.first_object->type != OBJT_VNODE &&
 624             (fs.first_object->flags & OBJ_TMPFS_NODE) == 0) ||
 625             (fs.first_object->flags & OBJ_MIGHTBEDIRTY) != 0)) {
 626                 VM_OBJECT_RLOCK(fs.first_object);
 627                 if ((prot & VM_PROT_WRITE) == 0 ||
 628                     (fs.first_object->type != OBJT_VNODE &&
 629                     (fs.first_object->flags & OBJ_TMPFS_NODE) == 0) ||
 630                     (fs.first_object->flags & OBJ_MIGHTBEDIRTY) != 0) {
 631                         rv = vm_fault_soft_fast(&fs, vaddr, prot, fault_type,
 632                             fault_flags, wired, m_hold);
 633                         if (rv == KERN_SUCCESS)
 634                                 return (rv);
 635                 }
 636                 if (!VM_OBJECT_TRYUPGRADE(fs.first_object)) {
 637                         VM_OBJECT_RUNLOCK(fs.first_object);
 638                         VM_OBJECT_WLOCK(fs.first_object);
 639                 }
 640         } else {
 641                 VM_OBJECT_WLOCK(fs.first_object);
 642         }
 643
 644         /*
 645          * Make a reference to this object to prevent its disposal while we
 646          * are messing with it.  Once we have the reference, the map is free
 647          * to be diddled.  Since objects reference their shadows (and copies),
 648          * they will stay around as well.
 649          *
 650          * Bump the paging-in-progress count to prevent size changes (e.g.
 651          * truncation operations) during I/O.
 652          */
 653         vm_object_reference_locked(fs.first_object);
 654         vm_object_pip_add(fs.first_object, 1);
 655
 656         fs.lookup_still_valid = true;
 657
 658         fs.first_m = NULL;
 659
 660         /*
 661          * Search for the page at object/offset.
 662          */
 663         fs.object = fs.first_object;
 664         fs.pindex = fs.first_pindex;
 665         while (TRUE) {
 666                 /*
 667                  * If the object is marked for imminent termination,
 668                  * we retry here, since the collapse pass has raced
 669                  * with us.  Otherwise, if we see terminally dead
 670                  * object, return fail.
 671                  */
 672                 if ((fs.object->flags & OBJ_DEAD) != 0) {
 673                         dead = fs.object->type == OBJT_DEAD;
 674                         unlock_and_deallocate(&fs);
 675                         if (dead)
 676                                 return (KERN_PROTECTION_FAILURE);
 677                         pause("vmf_de", 1);
 678                         goto RetryFault;
 679                 }
 680
 681                 /*
 682                  * See if page is resident
 683                  */
 684                 fs.m = vm_page_lookup(fs.object, fs.pindex);
 685                 if (fs.m != NULL) {
 686                         /*
 687                          * Wait/Retry if the page is busy.  We have to do this
 688                          * if the page is either exclusive or shared busy
 689                          * because the vm_pager may be using read busy for
 690                          * pageouts (and even pageins if it is the vnode
 691                          * pager), and we could end up trying to pagein and
 692                          * pageout the same page simultaneously.
 693                          *
 694                          * We can theoretically allow the busy case on a read
 695                          * fault if the page is marked valid, but since such
 696                          * pages are typically already pmap'd, putting that
 697                          * special case in might be more effort then it is
 698                          * worth.  We cannot under any circumstances mess
 699                          * around with a shared busied page except, perhaps,
 700                          * to pmap it.
 701                          */
 702                         if (vm_page_busied(fs.m)) {
 703                                 /*
 704                                  * Reference the page before unlocking and
 705                                  * sleeping so that the page daemon is less
 706                                  * likely to reclaim it.
 707                                  */
 708                                 vm_page_aflag_set(fs.m, PGA_REFERENCED);
 709                                 if (fs.object != fs.first_object) {
 710                                         if (!VM_OBJECT_TRYWLOCK(
 711                                             fs.first_object)) {
 712                                                 VM_OBJECT_WUNLOCK(fs.object);
 713                                                 VM_OBJECT_WLOCK(fs.first_object);
 714                                                 VM_OBJECT_WLOCK(fs.object);
 715                                         }
 716                                         vm_page_lock(fs.first_m);
 717                                         vm_page_free(fs.first_m);
 718                                         vm_page_unlock(fs.first_m);
 719                                         vm_object_pip_wakeup(fs.first_object);
 720                                         VM_OBJECT_WUNLOCK(fs.first_object);
 721                                         fs.first_m = NULL;
 722                                 }
 723                                 unlock_map(&fs);
 724                                 if (fs.m == vm_page_lookup(fs.object,
 725                                     fs.pindex)) {
 726                                         vm_page_sleep_if_busy(fs.m, "vmpfw");
 727                                 }
 728                                 vm_object_pip_wakeup(fs.object);
 729                                 VM_OBJECT_WUNLOCK(fs.object);
 730                                 VM_CNT_INC(v_intrans);
 731                                 vm_object_deallocate(fs.first_object);
 732                                 goto RetryFault;
 733                         }
 734
 735                         /*
 736                          * Mark page busy for other processes, and the
 737                          * pagedaemon.  If it still isn't completely valid
 738                          * (readable), jump to readrest, else break-out ( we
 739                          * found the page ).
 740                          */
 741                         vm_page_xbusy(fs.m);
 742                         if (fs.m->valid != VM_PAGE_BITS_ALL)
 743                                 goto readrest;
 744                         break; /* break to PAGE HAS BEEN FOUND */
 745                 }
 746                 KASSERT(fs.m == NULL, ("fs.m should be NULL, not %p", fs.m));
 747
 748                 /*
 749                  * Page is not resident.  If the pager might contain the page
 750                  * or this is the beginning of the search, allocate a new
 751                  * page.  (Default objects are zero-fill, so there is no real
 752                  * pager for them.)
 753                  */
 754                 if (fs.object->type != OBJT_DEFAULT ||
 755                     fs.object == fs.first_object) {
 756                         if (fs.pindex >= fs.object->size) {
 757                                 unlock_and_deallocate(&fs);
 758                                 return (KERN_PROTECTION_FAILURE);
 759                         }
 760
 761                         if (fs.object == fs.first_object &&
 762                             (fs.first_object->flags & OBJ_POPULATE) != 0 &&
 763                             fs.first_object->shadow_count == 0) {
 764                                 rv = vm_fault_populate(&fs, prot, fault_type,
 765                                     fault_flags, wired, m_hold);
 766                                 switch (rv) {
 767                                 case KERN_SUCCESS:
 768                                 case KERN_FAILURE:
 769                                         unlock_and_deallocate(&fs);
 770                                         return (rv);
 771                                 case KERN_RESOURCE_SHORTAGE:
 772                                         unlock_and_deallocate(&fs);
 773                                         goto RetryFault;
 774                                 case KERN_NOT_RECEIVER:
 775                                         /*
 776                                          * Pager's populate() method
 777                                          * returned VM_PAGER_BAD.
 778                                          */
 779                                         break;
 780                                 default:
 781                                         panic("inconsistent return codes");
 782                                 }
 783                         }
 784
 785                         /*
 786                          * Allocate a new page for this object/offset pair.
 787                          *
 788                          * Unlocked read of the p_flag is harmless. At
 789                          * worst, the P_KILLED might be not observed
 790                          * there, and allocation can fail, causing
 791                          * restart and new reading of the p_flag.
 792                          */
 793                         if (!vm_page_count_severe() || P_KILLED(curproc)) {
 794 #if VM_NRESERVLEVEL > 0
 795                                 vm_object_color(fs.object, atop(vaddr) -
 796                                     fs.pindex);
 797 #endif
 798                                 alloc_req = P_KILLED(curproc) ?
 799                                     VM_ALLOC_SYSTEM : VM_ALLOC_NORMAL;
 800                                 if (fs.object->type != OBJT_VNODE &&
 801                                     fs.object->backing_object == NULL)
 802                                         alloc_req |= VM_ALLOC_ZERO;
 803                                 fs.m = vm_page_alloc(fs.object, fs.pindex,
 804                                     alloc_req);
 805                         }
 806                         if (fs.m == NULL) {
 807                                 unlock_and_deallocate(&fs);
 808                                 vm_waitpfault();
 809                                 goto RetryFault;
 810                         }
 811                 }
 812
 813 readrest:
 814                 /*
 815                  * At this point, we have either allocated a new page or found
 816                  * an existing page that is only partially valid.
 817                  *
 818                  * We hold a reference on the current object and the page is
 819                  * exclusive busied.
 820                  */
 821
 822                 /*
 823                  * If the pager for the current object might have the page,
 824                  * then determine the number of additional pages to read and
 825                  * potentially reprioritize previously read pages for earlier
 826                  * reclamation.  These operations should only be performed
 827                  * once per page fault.  Even if the current pager doesn't
 828                  * have the page, the number of additional pages to read will
 829                  * apply to subsequent objects in the shadow chain.
 830                  */
 831                 if (fs.object->type != OBJT_DEFAULT && nera == -1 &&
 832                     !P_KILLED(curproc)) {
 833                         KASSERT(fs.lookup_still_valid, ("map unlocked"));
 834                         era = fs.entry->read_ahead;
 835                         behavior = vm_map_entry_behavior(fs.entry);
 836                         if (behavior == MAP_ENTRY_BEHAV_RANDOM) {
 837                                 nera = 0;
 838                         } else if (behavior == MAP_ENTRY_BEHAV_SEQUENTIAL) {
 839                                 nera = VM_FAULT_READ_AHEAD_MAX;
 840                                 if (vaddr == fs.entry->next_read)
 841                                         vm_fault_dontneed(&fs, vaddr, nera);
 842                         } else if (vaddr == fs.entry->next_read) {
 843                                 /*
 844                                  * This is a sequential fault.  Arithmetically
 845                                  * increase the requested number of pages in
 846                                  * the read-ahead window.  The requested
 847                                  * number of pages is "# of sequential faults
 848                                  * x (read ahead min + 1) + read ahead min"
 849                                  */
 850                                 nera = VM_FAULT_READ_AHEAD_MIN;
 851                                 if (era > 0) {
 852                                         nera += era + 1;
 853                                         if (nera > VM_FAULT_READ_AHEAD_MAX)
 854                                                 nera = VM_FAULT_READ_AHEAD_MAX;
 855                                 }
 856                                 if (era == VM_FAULT_READ_AHEAD_MAX)
 857                                         vm_fault_dontneed(&fs, vaddr, nera);
 858                         } else {
 859                                 /*
 860                                  * This is a non-sequential fault.
 861                                  */
 862                                 nera = 0;
 863                         }
 864                         if (era != nera) {
 865                                 /*
 866                                  * A read lock on the map suffices to update
 867                                  * the read ahead count safely.
 868                                  */
 869                                 fs.entry->read_ahead = nera;
 870                         }
 871
 872                         /*
 873                          * Prepare for unlocking the map.  Save the map
 874                          * entry's start and end addresses, which are used to
 875                          * optimize the size of the pager operation below.
 876                          * Even if the map entry's addresses change after
 877                          * unlocking the map, using the saved addresses is
 878                          * safe.
 879                          */
 880                         e_start = fs.entry->start;
 881                         e_end = fs.entry->end;
 882                 }
 883
 884                 /*
 885                  * Call the pager to retrieve the page if there is a chance
 886                  * that the pager has it, and potentially retrieve additional
 887                  * pages at the same time.
 888                  */
 889                 if (fs.object->type != OBJT_DEFAULT) {
 890                         /*
 891                          * Release the map lock before locking the vnode or
 892                          * sleeping in the pager.  (If the current object has
 893                          * a shadow, then an earlier iteration of this loop
 894                          * may have already unlocked the map.)
 895                          */
 896                         unlock_map(&fs);
 897
 898                         if (fs.object->type == OBJT_VNODE &&
 899                             (vp = fs.object->handle) != fs.vp) {
 900                                 /*
 901                                  * Perform an unlock in case the desired vnode
 902                                  * changed while the map was unlocked during a
 903                                  * retry.
 904                                  */
 905                                 unlock_vp(&fs);
 906
 907                                 locked = VOP_ISLOCKED(vp);
 908                                 if (locked != LK_EXCLUSIVE)
 909                                         locked = LK_SHARED;
 910
 911                                 /*
 912                                  * We must not sleep acquiring the vnode lock
 913                                  * while we have the page exclusive busied or
 914                                  * the object's paging-in-progress count
 915                                  * incremented.  Otherwise, we could deadlock.
 916                                  */
 917                                 error = vget(vp, locked | LK_CANRECURSE |
 918                                     LK_NOWAIT, curthread);
 919                                 if (error != 0) {
 920                                         vhold(vp);
 921                                         release_page(&fs);
 922                                         unlock_and_deallocate(&fs);
 923                                         error = vget(vp, locked | LK_RETRY |
 924                                             LK_CANRECURSE, curthread);
 925                                         vdrop(vp);
 926                                         fs.vp = vp;
 927                                         KASSERT(error == 0,
 928                                             ("vm_fault: vget failed"));
 929                                         goto RetryFault;
 930                                 }
 931                                 fs.vp = vp;
 932                         }
 933                         KASSERT(fs.vp == NULL || !fs.map->system_map,
 934                             ("vm_fault: vnode-backed object mapped by system map"));
 935
 936                         /*
 937                          * Page in the requested page and hint the pager,
 938                          * that it may bring up surrounding pages.
 939                          */
 940                         if (nera == -1 || behavior == MAP_ENTRY_BEHAV_RANDOM ||
 941                             P_KILLED(curproc)) {
 942                                 behind = 0;
 943                                 ahead = 0;
 944                         } else {
 945                                 /* Is this a sequential fault? */
 946                                 if (nera > 0) {
 947                                         behind = 0;
 948                                         ahead = nera;
 949                                 } else {
 950                                         /*
 951                                          * Request a cluster of pages that is
 952                                          * aligned to a VM_FAULT_READ_DEFAULT
 953                                          * page offset boundary within the
 954                                          * object.  Alignment to a page offset
 955                                          * boundary is more likely to coincide
 956                                          * with the underlying file system
 957                                          * block than alignment to a virtual
 958                                          * address boundary.
 959                                          */
 960                                         cluster_offset = fs.pindex %
 961                                             VM_FAULT_READ_DEFAULT;
 962                                         behind = ulmin(cluster_offset,
 963                                             atop(vaddr - e_start));
 964                                         ahead = VM_FAULT_READ_DEFAULT - 1 -
 965                                             cluster_offset;
 966                                 }
 967                                 ahead = ulmin(ahead, atop(e_end - vaddr) - 1);
 968                         }
 969                         rv = vm_pager_get_pages(fs.object, &fs.m, 1,
 970                             &behind, &ahead);
 971                         if (rv == VM_PAGER_OK) {
 972                                 faultcount = behind + 1 + ahead;
 973                                 hardfault = true;
 974                                 break; /* break to PAGE HAS BEEN FOUND */
 975                         }
 976                         if (rv == VM_PAGER_ERROR)
 977                                 printf("vm_fault: pager read error, pid %d (%s)\n",
 978                                     curproc->p_pid, curproc->p_comm);
 979
 980                         /*
 981                          * If an I/O error occurred or the requested page was
 982                          * outside the range of the pager, clean up and return
 983                          * an error.
 984                          */
 985                         if (rv == VM_PAGER_ERROR || rv == VM_PAGER_BAD) {
 986                                 vm_page_lock(fs.m);
 987                                 if (fs.m->wire_count == 0)
 988                                         vm_page_free(fs.m);
 989                                 else
 990                                         vm_page_xunbusy_maybelocked(fs.m);
 991                                 vm_page_unlock(fs.m);
 992                                 fs.m = NULL;
 993                                 unlock_and_deallocate(&fs);
 994                                 return (rv == VM_PAGER_ERROR ? KERN_FAILURE :
 995                                     KERN_PROTECTION_FAILURE);
 996                         }
 997
 998                         /*
 999                          * The requested page does not exist at this object/
1000                          * offset.  Remove the invalid page from the object,
1001                          * waking up anyone waiting for it, and continue on to
1002                          * the next object.  However, if this is the top-level
1003                          * object, we must leave the busy page in place to
1004                          * prevent another process from rushing past us, and
1005                          * inserting the page in that object at the same time
1006                          * that we are.
1007                          */
1008                         if (fs.object != fs.first_object) {
1009                                 vm_page_lock(fs.m);
1010                                 if (fs.m->wire_count == 0)
1011                                         vm_page_free(fs.m);
1012                                 else
1013                                         vm_page_xunbusy_maybelocked(fs.m);
1014                                 vm_page_unlock(fs.m);
1015                                 fs.m = NULL;
1016                         }
1017                 }
1018
1019                 /*
1020                  * We get here if the object has default pager (or unwiring)
1021                  * or the pager doesn't have the page.
1022                  */
1023                 if (fs.object == fs.first_object)
1024                         fs.first_m = fs.m;
1025
1026                 /*
1027                  * Move on to the next object.  Lock the next object before
1028                  * unlocking the current one.
1029                  */
1030                 next_object = fs.object->backing_object;
1031                 if (next_object == NULL) {
1032                         /*
1033                          * If there's no object left, fill the page in the top
1034                          * object with zeros.
1035                          */
1036                         if (fs.object != fs.first_object) {
1037                                 vm_object_pip_wakeup(fs.object);
1038                                 VM_OBJECT_WUNLOCK(fs.object);
1039
1040                                 fs.object = fs.first_object;
1041                                 fs.pindex = fs.first_pindex;
1042                                 fs.m = fs.first_m;
1043                                 VM_OBJECT_WLOCK(fs.object);
1044                         }
1045                         fs.first_m = NULL;
1046
1047                         /*
1048                          * Zero the page if necessary and mark it valid.
1049                          */
1050                         if ((fs.m->flags & PG_ZERO) == 0) {
1051                                 pmap_zero_page(fs.m);
1052                         } else {
1053                                 VM_CNT_INC(v_ozfod);
1054                         }
1055                         VM_CNT_INC(v_zfod);
1056                         fs.m->valid = VM_PAGE_BITS_ALL;
1057                         /* Don't try to prefault neighboring pages. */
1058                         faultcount = 1;
1059                         break;  /* break to PAGE HAS BEEN FOUND */
1060                 } else {
1061                         KASSERT(fs.object != next_object,
1062                             ("object loop %p", next_object));
1063                         VM_OBJECT_WLOCK(next_object);
1064                         vm_object_pip_add(next_object, 1);
1065                         if (fs.object != fs.first_object)
1066                                 vm_object_pip_wakeup(fs.object);
1067                         fs.pindex +=
1068                             OFF_TO_IDX(fs.object->backing_object_offset);
1069                         VM_OBJECT_WUNLOCK(fs.object);
1070                         fs.object = next_object;
1071                 }
1072         }
1073
1074         vm_page_assert_xbusied(fs.m);
1075
1076         /*
1077          * PAGE HAS BEEN FOUND. [Loop invariant still holds -- the object lock
1078          * is held.]
1079          */
1080
1081         /*
1082          * If the page is being written, but isn't already owned by the
1083          * top-level object, we have to copy it into a new page owned by the
1084          * top-level object.
1085          */
1086         if (fs.object != fs.first_object) {
1087                 /*
1088                  * We only really need to copy if we want to write it.
1089                  */
1090                 if ((fault_type & (VM_PROT_COPY | VM_PROT_WRITE)) != 0) {
1091                         /*
1092                          * This allows pages to be virtually copied from a
1093                          * backing_object into the first_object, where the
1094                          * backing object has no other refs to it, and cannot
1095                          * gain any more refs.  Instead of a bcopy, we just
1096                          * move the page from the backing object to the
1097                          * first object.  Note that we must mark the page
1098                          * dirty in the first object so that it will go out
1099                          * to swap when needed.
1100                          */
1101                         is_first_object_locked = false;
1102                         if (
1103                                 /*
1104                                  * Only one shadow object
1105                                  */
1106                                 (fs.object->shadow_count == 1) &&
1107                                 /*
1108                                  * No COW refs, except us
1109                                  */
1110                                 (fs.object->ref_count == 1) &&
1111                                 /*
1112                                  * No one else can look this object up
1113                                  */
1114                                 (fs.object->handle == NULL) &&
1115                                 /*
1116                                  * No other ways to look the object up
1117                                  */
1118                                 ((fs.object->type == OBJT_DEFAULT) ||
1119                                  (fs.object->type == OBJT_SWAP)) &&
1120                             (is_first_object_locked = VM_OBJECT_TRYWLOCK(fs.first_object)) &&
1121                                 /*
1122                                  * We don't chase down the shadow chain
1123                                  */
1124                             fs.object == fs.first_object->backing_object) {
1125                                 vm_page_lock(fs.m);
1126                                 vm_page_remque(fs.m);
1127                                 vm_page_remove(fs.m);
1128                                 vm_page_unlock(fs.m);
1129                                 vm_page_lock(fs.first_m);
1130                                 vm_page_replace_checked(fs.m, fs.first_object,
1131                                     fs.first_pindex, fs.first_m);
1132                                 vm_page_free(fs.first_m);
1133                                 vm_page_unlock(fs.first_m);
1134                                 vm_page_dirty(fs.m);
1135 #if VM_NRESERVLEVEL > 0
1136                                 /*
1137                                  * Rename the reservation.
1138                                  */
1139                                 vm_reserv_rename(fs.m, fs.first_object,
1140                                     fs.object, OFF_TO_IDX(
1141                                     fs.first_object->backing_object_offset));
1142 #endif
1143                                 /*
1144                                  * Removing the page from the backing object
1145                                  * unbusied it.
1146                                  */
1147                                 vm_page_xbusy(fs.m);
1148                                 fs.first_m = fs.m;
1149                                 fs.m = NULL;
1150                                 VM_CNT_INC(v_cow_optim);
1151                         } else {
1152                                 /*
1153                                  * Oh, well, lets copy it.
1154                                  */
1155                                 pmap_copy_page(fs.m, fs.first_m);
1156                                 fs.first_m->valid = VM_PAGE_BITS_ALL;
1157                                 if (wired && (fault_flags &
1158                                     VM_FAULT_WIRE) == 0) {
1159                                         vm_page_lock(fs.first_m);
1160                                         vm_page_wire(fs.first_m);
1161                                         vm_page_unlock(fs.first_m);
1162
1163                                         vm_page_lock(fs.m);
1164                                         vm_page_unwire(fs.m, PQ_INACTIVE);
1165                                         vm_page_unlock(fs.m);
1166                                 }
1167                                 /*
1168                                  * We no longer need the old page or object.
1169                                  */
1170                                 release_page(&fs);
1171                         }
1172                         /*
1173                          * fs.object != fs.first_object due to above
1174                          * conditional
1175                          */
1176                         vm_object_pip_wakeup(fs.object);
1177                         VM_OBJECT_WUNLOCK(fs.object);
1178                         /*
1179                          * Only use the new page below...
1180                          */
1181                         fs.object = fs.first_object;
1182                         fs.pindex = fs.first_pindex;
1183                         fs.m = fs.first_m;
1184                         if (!is_first_object_locked)
1185                                 VM_OBJECT_WLOCK(fs.object);
1186                         VM_CNT_INC(v_cow_faults);
1187                         curthread->td_cow++;
1188                 } else {
1189                         prot &= ~VM_PROT_WRITE;
1190                 }
1191         }
1192
1193         /*
1194          * We must verify that the maps have not changed since our last
1195          * lookup.
1196          */
1197         if (!fs.lookup_still_valid) {
1198                 if (!vm_map_trylock_read(fs.map)) {
1199                         release_page(&fs);
1200                         unlock_and_deallocate(&fs);
1201                         goto RetryFault;
1202                 }
1203                 fs.lookup_still_valid = true;
1204                 if (fs.map->timestamp != fs.map_generation) {
1205                         result = vm_map_lookup_locked(&fs.map, vaddr, fault_type,
1206                             &fs.entry, &retry_object, &retry_pindex, &retry_prot, &wired);
1207
1208                         /*
1209                          * If we don't need the page any longer, put it on the inactive
1210                          * list (the easiest thing to do here).  If no one needs it,
1211                          * pageout will grab it eventually.
1212                          */
1213                         if (result != KERN_SUCCESS) {
1214                                 release_page(&fs);
1215                                 unlock_and_deallocate(&fs);
1216
1217                                 /*
1218                                  * If retry of map lookup would have blocked then
1219                                  * retry fault from start.
1220                                  */
1221                                 if (result == KERN_FAILURE)
1222                                         goto RetryFault;
1223                                 return (result);
1224                         }
1225                         if ((retry_object != fs.first_object) ||
1226                             (retry_pindex != fs.first_pindex)) {
1227                                 release_page(&fs);
1228                                 unlock_and_deallocate(&fs);
1229                                 goto RetryFault;
1230                         }
1231
1232                         /*
1233                          * Check whether the protection has changed or the object has
1234                          * been copied while we left the map unlocked. Changing from
1235                          * read to write permission is OK - we leave the page
1236                          * write-protected, and catch the write fault. Changing from
1237                          * write to read permission means that we can't mark the page
1238                          * write-enabled after all.
1239                          */
1240                         prot &= retry_prot;
1241                         fault_type &= retry_prot;
1242                         if (prot == 0) {
1243                                 release_page(&fs);
1244                                 unlock_and_deallocate(&fs);
1245                                 goto RetryFault;
1246                         }
1247
1248                         /* Reassert because wired may have changed. */
1249                         KASSERT(wired || (fault_flags & VM_FAULT_WIRE) == 0,
1250                             ("!wired && VM_FAULT_WIRE"));
1251                 }
1252         }
1253
1254         /*
1255          * If the page was filled by a pager, save the virtual address that
1256          * should be faulted on next under a sequential access pattern to the
1257          * map entry.  A read lock on the map suffices to update this address
1258          * safely.
1259          */
1260         if (hardfault)
1261                 fs.entry->next_read = vaddr + ptoa(ahead) + PAGE_SIZE;
1262
1263         vm_fault_dirty(fs.entry, fs.m, prot, fault_type, fault_flags, true);
1264         vm_page_assert_xbusied(fs.m);
1265
1266         /*
1267          * Page must be completely valid or it is not fit to
1268          * map into user space.  vm_pager_get_pages() ensures this.
1269          */
1270         KASSERT(fs.m->valid == VM_PAGE_BITS_ALL,
1271             ("vm_fault: page %p partially invalid", fs.m));
1272         VM_OBJECT_WUNLOCK(fs.object);
1273
1274         /*
1275          * Put this page into the physical map.  We had to do the unlock above
1276          * because pmap_enter() may sleep.  We don't put the page
1277          * back on the active queue until later so that the pageout daemon
1278          * won't find it (yet).
1279          */
1280         pmap_enter(fs.map->pmap, vaddr, fs.m, prot,
1281             fault_type | (wired ? PMAP_ENTER_WIRED : 0), 0);
1282         if (faultcount != 1 && (fault_flags & VM_FAULT_WIRE) == 0 &&
1283             wired == 0)
1284                 vm_fault_prefault(&fs, vaddr,
1285                     faultcount > 0 ? behind : PFBAK,
1286                     faultcount > 0 ? ahead : PFFOR, false);
1287         VM_OBJECT_WLOCK(fs.object);
1288         vm_page_lock(fs.m);
1289
1290         /*
1291          * If the page is not wired down, then put it where the pageout daemon
1292          * can find it.
1293          */
1294         if ((fault_flags & VM_FAULT_WIRE) != 0)
1295                 vm_page_wire(fs.m);
1296         else
1297                 vm_page_activate(fs.m);
1298         if (m_hold != NULL) {
1299                 *m_hold = fs.m;
1300                 vm_page_hold(fs.m);
1301         }
1302         vm_page_unlock(fs.m);
1303         vm_page_xunbusy(fs.m);
1304
1305         /*
1306          * Unlock everything, and return
1307          */
1308         unlock_and_deallocate(&fs);
1309         if (hardfault) {
1310                 VM_CNT_INC(v_io_faults);
1311                 curthread->td_ru.ru_majflt++;
1312 #ifdef RACCT
1313                 if (racct_enable && fs.object->type == OBJT_VNODE) {
1314                         PROC_LOCK(curproc);
1315                         if ((fault_type & (VM_PROT_COPY | VM_PROT_WRITE)) != 0) {
1316                                 racct_add_force(curproc, RACCT_WRITEBPS,
1317                                     PAGE_SIZE + behind * PAGE_SIZE);
1318                                 racct_add_force(curproc, RACCT_WRITEIOPS, 1);
1319                         } else {
1320                                 racct_add_force(curproc, RACCT_READBPS,
1321                                     PAGE_SIZE + ahead * PAGE_SIZE);
1322                                 racct_add_force(curproc, RACCT_READIOPS, 1);
1323                         }
1324                         PROC_UNLOCK(curproc);
1325                 }
1326 #endif
1327         } else
1328                 curthread->td_ru.ru_minflt++;
1329
1330         return (KERN_SUCCESS);
1331 }
1332
1333 /*
1334  * Speed up the reclamation of pages that precede the faulting pindex within
1335  * the first object of the shadow chain.  Essentially, perform the equivalent
1336  * to madvise(..., MADV_DONTNEED) on a large cluster of pages that precedes
1337  * the faulting pindex by the cluster size when the pages read by vm_fault()
1338  * cross a cluster-size boundary.  The cluster size is the greater of the
1339  * smallest superpage size and VM_FAULT_DONTNEED_MIN.
1340  *
1341  * When "fs->first_object" is a shadow object, the pages in the backing object
1342  * that precede the faulting pindex are deactivated by vm_fault().  So, this
1343  * function must only be concerned with pages in the first object.
1344  */
1345 static void
1346 vm_fault_dontneed(const struct faultstate *fs, vm_offset_t vaddr, int ahead)
1347 {
1348         vm_map_entry_t entry;
1349         vm_object_t first_object, object;
1350         vm_offset_t end, start;
1351         vm_page_t m, m_next;
1352         vm_pindex_t pend, pstart;
1353         vm_size_t size;
1354
1355         object = fs->object;
1356         VM_OBJECT_ASSERT_WLOCKED(object);
1357         first_object = fs->first_object;
1358         if (first_object != object) {
1359                 if (!VM_OBJECT_TRYWLOCK(first_object)) {
1360                         VM_OBJECT_WUNLOCK(object);
1361                         VM_OBJECT_WLOCK(first_object);
1362                         VM_OBJECT_WLOCK(object);
1363                 }
1364         }
1365         /* Neither fictitious nor unmanaged pages can be reclaimed. */
1366         if ((first_object->flags & (OBJ_FICTITIOUS | OBJ_UNMANAGED)) == 0) {
1367                 size = VM_FAULT_DONTNEED_MIN;
1368                 if (MAXPAGESIZES > 1 && size < pagesizes[1])
1369                         size = pagesizes[1];
1370                 end = rounddown2(vaddr, size);
1371                 if (vaddr - end >= size - PAGE_SIZE - ptoa(ahead) &&
1372                     (entry = fs->entry)->start < end) {
1373                         if (end - entry->start < size)
1374                                 start = entry->start;
1375                         else
1376                                 start = end - size;
1377                         pmap_advise(fs->map->pmap, start, end, MADV_DONTNEED);
1378                         pstart = OFF_TO_IDX(entry->offset) + atop(start -
1379                             entry->start);
1380                         m_next = vm_page_find_least(first_object, pstart);
1381                         pend = OFF_TO_IDX(entry->offset) + atop(end -
1382                             entry->start);
1383                         while ((m = m_next) != NULL && m->pindex < pend) {
1384                                 m_next = TAILQ_NEXT(m, listq);
1385                                 if (m->valid != VM_PAGE_BITS_ALL ||
1386                                     vm_page_busied(m))
1387                                         continue;
1388
1389                                 /*
1390                                  * Don't clear PGA_REFERENCED, since it would
1391                                  * likely represent a reference by a different
1392                                  * process.
1393                                  *
1394                                  * Typically, at this point, prefetched pages
1395                                  * are still in the inactive queue.  Only
1396                                  * pages that triggered page faults are in the
1397                                  * active queue.
1398                                  */
1399                                 vm_page_lock(m);
1400                                 if (!vm_page_inactive(m))
1401                                         vm_page_deactivate(m);
1402                                 vm_page_unlock(m);
1403                         }
1404                 }
1405         }
1406         if (first_object != object)
1407                 VM_OBJECT_WUNLOCK(first_object);
1408 }
1409
1410 /*
1411  * vm_fault_prefault provides a quick way of clustering
1412  * pagefaults into a processes address space.  It is a "cousin"
1413  * of vm_map_pmap_enter, except it runs at page fault time instead
1414  * of mmap time.
1415  */
1416 static void
1417 vm_fault_prefault(const struct faultstate *fs, vm_offset_t addra,
1418     int backward, int forward, bool obj_locked)
1419 {
1420         pmap_t pmap;
1421         vm_map_entry_t entry;
1422         vm_object_t backing_object, lobject;
1423         vm_offset_t addr, starta;
1424         vm_pindex_t pindex;
1425         vm_page_t m;
1426         int i;
1427
1428         pmap = fs->map->pmap;
1429         if (pmap != vmspace_pmap(curthread->td_proc->p_vmspace))
1430                 return;
1431
1432         entry = fs->entry;
1433
1434         if (addra < backward * PAGE_SIZE) {
1435                 starta = entry->start;
1436         } else {
1437                 starta = addra - backward * PAGE_SIZE;
1438                 if (starta < entry->start)
1439                         starta = entry->start;
1440         }
1441
1442         /*
1443          * Generate the sequence of virtual addresses that are candidates for
1444          * prefaulting in an outward spiral from the faulting virtual address,
1445          * "addra".  Specifically, the sequence is "addra - PAGE_SIZE", "addra
1446          * + PAGE_SIZE", "addra - 2 * PAGE_SIZE", "addra + 2 * PAGE_SIZE", ...
1447          * If the candidate address doesn't have a backing physical page, then
1448          * the loop immediately terminates.
1449          */
1450         for (i = 0; i < 2 * imax(backward, forward); i++) {
1451                 addr = addra + ((i >> 1) + 1) * ((i & 1) == 0 ? -PAGE_SIZE :
1452                     PAGE_SIZE);
1453                 if (addr > addra + forward * PAGE_SIZE)
1454                         addr = 0;
1455
1456                 if (addr < starta || addr >= entry->end)
1457                         continue;
1458
1459                 if (!pmap_is_prefaultable(pmap, addr))
1460                         continue;
1461
1462                 pindex = ((addr - entry->start) + entry->offset) >> PAGE_SHIFT;
1463                 lobject = entry->object.vm_object;
1464                 if (!obj_locked)
1465                         VM_OBJECT_RLOCK(lobject);
1466                 while ((m = vm_page_lookup(lobject, pindex)) == NULL &&
1467                     lobject->type == OBJT_DEFAULT &&
1468                     (backing_object = lobject->backing_object) != NULL) {
1469                         KASSERT((lobject->backing_object_offset & PAGE_MASK) ==
1470                             0, ("vm_fault_prefault: unaligned object offset"));
1471                         pindex += lobject->backing_object_offset >> PAGE_SHIFT;
1472                         VM_OBJECT_RLOCK(backing_object);
1473                         if (!obj_locked || lobject != entry->object.vm_object)
1474                                 VM_OBJECT_RUNLOCK(lobject);
1475                         lobject = backing_object;
1476                 }
1477                 if (m == NULL) {
1478                         if (!obj_locked || lobject != entry->object.vm_object)
1479                                 VM_OBJECT_RUNLOCK(lobject);
1480                         break;
1481                 }
1482                 if (m->valid == VM_PAGE_BITS_ALL &&
1483                     (m->flags & PG_FICTITIOUS) == 0)
1484                         pmap_enter_quick(pmap, addr, m, entry->protection);
1485                 if (!obj_locked || lobject != entry->object.vm_object)
1486                         VM_OBJECT_RUNLOCK(lobject);
1487         }
1488 }
1489
1490 /*
1491  * Hold each of the physical pages that are mapped by the specified range of
1492  * virtual addresses, ["addr", "addr" + "len"), if those mappings are valid
1493  * and allow the specified types of access, "prot".  If all of the implied
1494  * pages are successfully held, then the number of held pages is returned
1495  * together with pointers to those pages in the array "ma".  However, if any
1496  * of the pages cannot be held, -1 is returned.
1497  */
1498 int
1499 vm_fault_quick_hold_pages(vm_map_t map, vm_offset_t addr, vm_size_t len,
1500     vm_prot_t prot, vm_page_t *ma, int max_count)
1501 {
1502         vm_offset_t end, va;
1503         vm_page_t *mp;
1504         int count;
1505         boolean_t pmap_failed;
1506
1507         if (len == 0)
1508                 return (0);
1509         end = round_page(addr + len);
1510         addr = trunc_page(addr);
1511
1512         /*
1513          * Check for illegal addresses.
1514          */
1515         if (addr < vm_map_min(map) || addr > end || end > vm_map_max(map))
1516                 return (-1);
1517
1518         if (atop(end - addr) > max_count)
1519                 panic("vm_fault_quick_hold_pages: count > max_count");
1520         count = atop(end - addr);
1521
1522         /*
1523          * Most likely, the physical pages are resident in the pmap, so it is
1524          * faster to try pmap_extract_and_hold() first.
1525          */
1526         pmap_failed = FALSE;
1527         for (mp = ma, va = addr; va < end; mp++, va += PAGE_SIZE) {
1528                 *mp = pmap_extract_and_hold(map->pmap, va, prot);
1529                 if (*mp == NULL)
1530                         pmap_failed = TRUE;
1531                 else if ((prot & VM_PROT_WRITE) != 0 &&
1532                     (*mp)->dirty != VM_PAGE_BITS_ALL) {
1533                         /*
1534                          * Explicitly dirty the physical page.  Otherwise, the
1535                          * caller's changes may go unnoticed because they are
1536                          * performed through an unmanaged mapping or by a DMA
1537                          * operation.
1538                          *
1539                          * The object lock is not held here.
1540                          * See vm_page_clear_dirty_mask().
1541                          */
1542                         vm_page_dirty(*mp);
1543                 }
1544         }
1545         if (pmap_failed) {
1546                 /*
1547                  * One or more pages could not be held by the pmap.  Either no
1548                  * page was mapped at the specified virtual address or that
1549                  * mapping had insufficient permissions.  Attempt to fault in
1550                  * and hold these pages.
1551                  *
1552                  * If vm_fault_disable_pagefaults() was called,
1553                  * i.e., TDP_NOFAULTING is set, we must not sleep nor
1554                  * acquire MD VM locks, which means we must not call
1555                  * vm_fault_hold().  Some (out of tree) callers mark
1556                  * too wide a code area with vm_fault_disable_pagefaults()
1557                  * already, use the VM_PROT_QUICK_NOFAULT flag to request
1558                  * the proper behaviour explicitly.
1559                  */
1560                 if ((prot & VM_PROT_QUICK_NOFAULT) != 0 &&
1561                     (curthread->td_pflags & TDP_NOFAULTING) != 0)
1562                         goto error;
1563                 for (mp = ma, va = addr; va < end; mp++, va += PAGE_SIZE)
1564                         if (*mp == NULL && vm_fault_hold(map, va, prot,
1565                             VM_FAULT_NORMAL, mp) != KERN_SUCCESS)
1566                                 goto error;
1567         }
1568         return (count);
1569 error:
1570         for (mp = ma; mp < ma + count; mp++)
1571                 if (*mp != NULL) {
1572                         vm_page_lock(*mp);
1573                         vm_page_unhold(*mp);
1574                         vm_page_unlock(*mp);
1575                 }
1576         return (-1);
1577 }
1578
1579 /*
1580  *      Routine:
1581  *              vm_fault_copy_entry
1582  *      Function:
1583  *              Create new shadow object backing dst_entry with private copy of
1584  *              all underlying pages. When src_entry is equal to dst_entry,
1585  *              function implements COW for wired-down map entry. Otherwise,
1586  *              it forks wired entry into dst_map.
1587  *
1588  *      In/out conditions:
1589  *              The source and destination maps must be locked for write.
1590  *              The source map entry must be wired down (or be a sharing map
1591  *              entry corresponding to a main map entry that is wired down).
1592  */
1593 void
1594 vm_fault_copy_entry(vm_map_t dst_map, vm_map_t src_map,
1595     vm_map_entry_t dst_entry, vm_map_entry_t src_entry,
1596     vm_ooffset_t *fork_charge)
1597 {
1598         vm_object_t backing_object, dst_object, object, src_object;
1599         vm_pindex_t dst_pindex, pindex, src_pindex;
1600         vm_prot_t access, prot;
1601         vm_offset_t vaddr;
1602         vm_page_t dst_m;
1603         vm_page_t src_m;
1604         boolean_t upgrade;
1605
1606 #ifdef  lint
1607         src_map++;
1608 #endif  /* lint */
1609
1610         upgrade = src_entry == dst_entry;
1611         access = prot = dst_entry->protection;
1612
1613         src_object = src_entry->object.vm_object;
1614         src_pindex = OFF_TO_IDX(src_entry->offset);
1615
1616         if (upgrade && (dst_entry->eflags & MAP_ENTRY_NEEDS_COPY) == 0) {
1617                 dst_object = src_object;
1618                 vm_object_reference(dst_object);
1619         } else {
1620                 /*
1621                  * Create the top-level object for the destination entry. (Doesn't
1622                  * actually shadow anything - we copy the pages directly.)
1623                  */
1624                 dst_object = vm_object_allocate(OBJT_DEFAULT,
1625                     atop(dst_entry->end - dst_entry->start));
1626 #if VM_NRESERVLEVEL > 0
1627                 dst_object->flags |= OBJ_COLORED;
1628                 dst_object->pg_color = atop(dst_entry->start);
1629 #endif
1630         }
1631
1632         VM_OBJECT_WLOCK(dst_object);
1633         KASSERT(upgrade || dst_entry->object.vm_object == NULL,
1634             ("vm_fault_copy_entry: vm_object not NULL"));
1635         if (src_object != dst_object) {
1636                 dst_object->domain = src_object->domain;
1637                 dst_entry->object.vm_object = dst_object;
1638                 dst_entry->offset = 0;
1639                 dst_object->charge = dst_entry->end - dst_entry->start;
1640         }
1641         if (fork_charge != NULL) {
1642                 KASSERT(dst_entry->cred == NULL,
1643                     ("vm_fault_copy_entry: leaked swp charge"));
1644                 dst_object->cred = curthread->td_ucred;
1645                 crhold(dst_object->cred);
1646                 *fork_charge += dst_object->charge;
1647         } else if (dst_object->cred == NULL) {
1648                 KASSERT(dst_entry->cred != NULL, ("no cred for entry %p",
1649                     dst_entry));
1650                 dst_object->cred = dst_entry->cred;
1651                 dst_entry->cred = NULL;
1652         }
1653
1654         /*
1655          * If not an upgrade, then enter the mappings in the pmap as
1656          * read and/or execute accesses.  Otherwise, enter them as
1657          * write accesses.
1658          *
1659          * A writeable large page mapping is only created if all of
1660          * the constituent small page mappings are modified. Marking
1661          * PTEs as modified on inception allows promotion to happen
1662          * without taking potentially large number of soft faults.
1663          */
1664         if (!upgrade)
1665                 access &= ~VM_PROT_WRITE;
1666
1667         /*
1668          * Loop through all of the virtual pages within the entry's
1669          * range, copying each page from the source object to the
1670          * destination object.  Since the source is wired, those pages
1671          * must exist.  In contrast, the destination is pageable.
1672          * Since the destination object doesn't share any backing storage
1673          * with the source object, all of its pages must be dirtied,
1674          * regardless of whether they can be written.
1675          */
1676         for (vaddr = dst_entry->start, dst_pindex = 0;
1677             vaddr < dst_entry->end;
1678             vaddr += PAGE_SIZE, dst_pindex++) {
1679 again:
1680                 /*
1681                  * Find the page in the source object, and copy it in.
1682                  * Because the source is wired down, the page will be
1683                  * in memory.
1684                  */
1685                 if (src_object != dst_object)
1686                         VM_OBJECT_RLOCK(src_object);
1687                 object = src_object;
1688                 pindex = src_pindex + dst_pindex;
1689                 while ((src_m = vm_page_lookup(object, pindex)) == NULL &&
1690                     (backing_object = object->backing_object) != NULL) {
1691                         /*
1692                          * Unless the source mapping is read-only or
1693                          * it is presently being upgraded from
1694                          * read-only, the first object in the shadow
1695                          * chain should provide all of the pages.  In
1696                          * other words, this loop body should never be
1697                          * executed when the source mapping is already
1698                          * read/write.
1699                          */
1700                         KASSERT((src_entry->protection & VM_PROT_WRITE) == 0 ||
1701                             upgrade,
1702                             ("vm_fault_copy_entry: main object missing page"));
1703
1704                         VM_OBJECT_RLOCK(backing_object);
1705                         pindex += OFF_TO_IDX(object->backing_object_offset);
1706                         if (object != dst_object)
1707                                 VM_OBJECT_RUNLOCK(object);
1708                         object = backing_object;
1709                 }
1710                 KASSERT(src_m != NULL, ("vm_fault_copy_entry: page missing"));
1711
1712                 if (object != dst_object) {
1713                         /*
1714                          * Allocate a page in the destination object.
1715                          */
1716                         dst_m = vm_page_alloc(dst_object, (src_object ==
1717                             dst_object ? src_pindex : 0) + dst_pindex,
1718                             VM_ALLOC_NORMAL);
1719                         if (dst_m == NULL) {
1720                                 VM_OBJECT_WUNLOCK(dst_object);
1721                                 VM_OBJECT_RUNLOCK(object);
1722                                 vm_wait(dst_object);
1723                                 VM_OBJECT_WLOCK(dst_object);
1724                                 goto again;
1725                         }
1726                         pmap_copy_page(src_m, dst_m);
1727                         VM_OBJECT_RUNLOCK(object);
1728                         dst_m->valid = VM_PAGE_BITS_ALL;
1729                         dst_m->dirty = VM_PAGE_BITS_ALL;
1730                 } else {
1731                         dst_m = src_m;
1732                         if (vm_page_sleep_if_busy(dst_m, "fltupg"))
1733                                 goto again;
1734                         vm_page_xbusy(dst_m);
1735                         KASSERT(dst_m->valid == VM_PAGE_BITS_ALL,
1736                             ("invalid dst page %p", dst_m));
1737                 }
1738                 VM_OBJECT_WUNLOCK(dst_object);
1739
1740                 /*
1741                  * Enter it in the pmap. If a wired, copy-on-write
1742                  * mapping is being replaced by a write-enabled
1743                  * mapping, then wire that new mapping.
1744                  */
1745                 pmap_enter(dst_map->pmap, vaddr, dst_m, prot,
1746                     access | (upgrade ? PMAP_ENTER_WIRED : 0), 0);
1747
1748                 /*
1749                  * Mark it no longer busy, and put it on the active list.
1750                  */
1751                 VM_OBJECT_WLOCK(dst_object);
1752
1753                 if (upgrade) {
1754                         if (src_m != dst_m) {
1755                                 vm_page_lock(src_m);
1756                                 vm_page_unwire(src_m, PQ_INACTIVE);
1757                                 vm_page_unlock(src_m);
1758                                 vm_page_lock(dst_m);
1759                                 vm_page_wire(dst_m);
1760                                 vm_page_unlock(dst_m);
1761                         } else {
1762                                 KASSERT(dst_m->wire_count > 0,
1763                                     ("dst_m %p is not wired", dst_m));
1764                         }
1765                 } else {
1766                         vm_page_lock(dst_m);
1767                         vm_page_activate(dst_m);
1768                         vm_page_unlock(dst_m);
1769                 }
1770                 vm_page_xunbusy(dst_m);
1771         }
1772         VM_OBJECT_WUNLOCK(dst_object);
1773         if (upgrade) {
1774                 dst_entry->eflags &= ~(MAP_ENTRY_COW | MAP_ENTRY_NEEDS_COPY);
1775                 vm_object_deallocate(src_object);
1776         }
1777 }
1778
1779 /*
1780  * Block entry into the machine-independent layer's page fault handler by
1781  * the calling thread.  Subsequent calls to vm_fault() by that thread will
1782  * return KERN_PROTECTION_FAILURE.  Enable machine-dependent handling of
1783  * spurious page faults.
1784  */
1785 int
1786 vm_fault_disable_pagefaults(void)
1787 {
1788
1789         return (curthread_pflags_set(TDP_NOFAULTING | TDP_RESETSPUR));
1790 }
1791
1792 void
1793 vm_fault_enable_pagefaults(int save)
1794 {
1795
1796         curthread_pflags_restore(save);
1797 }