sys/vm/vm_fault.c

   1 /*
   2  * Copyright (c) 1991, 1993
   3  *      The Regents of the University of California.  All rights reserved.
   4  * Copyright (c) 1994 John S. Dyson
   5  * All rights reserved.
   6  * Copyright (c) 1994 David Greenman
   7  * All rights reserved.
   8  *
   9  *
  10  * This code is derived from software contributed to Berkeley by
  11  * The Mach Operating System project at Carnegie-Mellon University.
  12  *
  13  * Redistribution and use in source and binary forms, with or without
  14  * modification, are permitted provided that the following conditions
  15  * are met:
  16  * 1. Redistributions of source code must retain the above copyright
  17  *    notice, this list of conditions and the following disclaimer.
  18  * 2. Redistributions in binary form must reproduce the above copyright
  19  *    notice, this list of conditions and the following disclaimer in the
  20  *    documentation and/or other materials provided with the distribution.
  21  * 3. All advertising materials mentioning features or use of this software
  22  *    must display the following acknowledgement:
  23  *      This product includes software developed by the University of
  24  *      California, Berkeley and its contributors.
  25  * 4. Neither the name of the University nor the names of its contributors
  26  *    may be used to endorse or promote products derived from this software
  27  *    without specific prior written permission.
  28  *
  29  * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
  30  * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
  31  * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
  32  * ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
  33  * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
  34  * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
  35  * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
  36  * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
  37  * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
  38  * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
  39  * SUCH DAMAGE.
  40  *
  41  *      from: @(#)vm_fault.c    8.4 (Berkeley) 1/12/94
  42  *
  43  *
  44  * Copyright (c) 1987, 1990 Carnegie-Mellon University.
  45  * All rights reserved.
  46  *
  47  * Authors: Avadis Tevanian, Jr., Michael Wayne Young
  48  *
  49  * Permission to use, copy, modify and distribute this software and
  50  * its documentation is hereby granted, provided that both the copyright
  51  * notice and this permission notice appear in all copies of the
  52  * software, derivative works or modified versions, and any portions
  53  * thereof, and that both notices appear in supporting documentation.
  54  *
  55  * CARNEGIE MELLON ALLOWS FREE USE OF THIS SOFTWARE IN ITS "AS IS"
  56  * CONDITION.  CARNEGIE MELLON DISCLAIMS ANY LIABILITY OF ANY KIND
  57  * FOR ANY DAMAGES WHATSOEVER RESULTING FROM THE USE OF THIS SOFTWARE.
  58  *
  59  * Carnegie Mellon requests users of this software to return to
  60  *
  61  *  Software Distribution Coordinator  or  Software.Distribution@CS.CMU.EDU
  62  *  School of Computer Science
  63  *  Carnegie Mellon University
  64  *  Pittsburgh PA 15213-3890
  65  *
  66  * any improvements or extensions that they make and grant Carnegie the
  67  * rights to redistribute these changes.
  68  *
  69  * $FreeBSD$
  70  */
  71
  72 /*
  73  *      Page fault handling module.
  74  */
  75
  76 #include <sys/param.h>
  77 #include <sys/systm.h>
  78 #include <sys/kernel.h>
  79 #include <sys/lock.h>
  80 #include <sys/mutex.h>
  81 #include <sys/proc.h>
  82 #include <sys/resourcevar.h>
  83 #include <sys/sysctl.h>
  84 #include <sys/vmmeter.h>
  85 #include <sys/vnode.h>
  86
  87 #include <vm/vm.h>
  88 #include <vm/vm_param.h>
  89 #include <vm/pmap.h>
  90 #include <vm/vm_map.h>
  91 #include <vm/vm_object.h>
  92 #include <vm/vm_page.h>
  93 #include <vm/vm_pageout.h>
  94 #include <vm/vm_kern.h>
  95 #include <vm/vm_pager.h>
  96 #include <vm/vnode_pager.h>
  97 #include <vm/vm_extern.h>
  98
  99 static int vm_fault_additional_pages __P((vm_page_t, int,
 100                                           int, vm_page_t *, int *));
 101
 102 #define VM_FAULT_READ_AHEAD 8
 103 #define VM_FAULT_READ_BEHIND 7
 104 #define VM_FAULT_READ (VM_FAULT_READ_AHEAD+VM_FAULT_READ_BEHIND+1)
 105
 106 struct faultstate {
 107         vm_page_t m;
 108         vm_object_t object;
 109         vm_pindex_t pindex;
 110         vm_page_t first_m;
 111         vm_object_t     first_object;
 112         vm_pindex_t first_pindex;
 113         vm_map_t map;
 114         vm_map_entry_t entry;
 115         int lookup_still_valid;
 116         struct vnode *vp;
 117 };
 118
 119 static __inline void
 120 release_page(struct faultstate *fs)
 121 {
 122         vm_page_wakeup(fs->m);
 123         vm_page_deactivate(fs->m);
 124         fs->m = NULL;
 125 }
 126
 127 static __inline void
 128 unlock_map(struct faultstate *fs)
 129 {
 130         if (fs->lookup_still_valid) {
 131                 vm_map_lookup_done(fs->map, fs->entry);
 132                 fs->lookup_still_valid = FALSE;
 133         }
 134 }
 135
 136 static void
 137 _unlock_things(struct faultstate *fs, int dealloc)
 138 {
 139         GIANT_REQUIRED;
 140         vm_object_pip_wakeup(fs->object);
 141         if (fs->object != fs->first_object) {
 142                 vm_page_free(fs->first_m);
 143                 vm_object_pip_wakeup(fs->first_object);
 144                 fs->first_m = NULL;
 145         }
 146         if (dealloc) {
 147                 vm_object_deallocate(fs->first_object);
 148         }
 149         unlock_map(fs);
 150         if (fs->vp != NULL) {
 151                 vput(fs->vp);
 152                 fs->vp = NULL;
 153         }
 154 }
 155
 156 #define unlock_things(fs) _unlock_things(fs, 0)
 157 #define unlock_and_deallocate(fs) _unlock_things(fs, 1)
 158
 159 /*
 160  * TRYPAGER - used by vm_fault to calculate whether the pager for the
 161  *            current object *might* contain the page.
 162  *
 163  *            default objects are zero-fill, there is no real pager.
 164  */
 165
 166 #define TRYPAGER        (fs.object->type != OBJT_DEFAULT && \
 167                         (((fault_flags & VM_FAULT_WIRE_MASK) == 0) || wired))
 168
 169 /*
 170  *      vm_fault:
 171  *
 172  *      Handle a page fault occurring at the given address,
 173  *      requiring the given permissions, in the map specified.
 174  *      If successful, the page is inserted into the
 175  *      associated physical map.
 176  *
 177  *      NOTE: the given address should be truncated to the
 178  *      proper page address.
 179  *
 180  *      KERN_SUCCESS is returned if the page fault is handled; otherwise,
 181  *      a standard error specifying why the fault is fatal is returned.
 182  *
 183  *
 184  *      The map in question must be referenced, and remains so.
 185  *      Caller may hold no locks.
 186  */
 187 static int vm_fault1 __P((vm_map_t, vm_offset_t, vm_prot_t, int));
 188
 189 int
 190 vm_fault(vm_map_t map, vm_offset_t vaddr, vm_prot_t fault_type,
 191          int fault_flags)
 192 {
 193         int ret;
 194
 195         mtx_lock(&Giant);
 196         /* GIANT_REQUIRED */
 197
 198         ret = vm_fault1(map, vaddr, fault_type, fault_flags);
 199         mtx_unlock(&Giant);
 200         return (ret);
 201 }
 202
 203 static int
 204 vm_fault1(vm_map_t map, vm_offset_t vaddr, vm_prot_t fault_type,
 205           int fault_flags)
 206 {
 207         vm_prot_t prot;
 208         int result;
 209         boolean_t wired;
 210         int map_generation;
 211         vm_object_t next_object;
 212         vm_page_t marray[VM_FAULT_READ];
 213         int hardfault;
 214         int faultcount;
 215         struct faultstate fs;
 216
 217         GIANT_REQUIRED;
 218
 219         cnt.v_vm_faults++;
 220         hardfault = 0;
 221
 222 RetryFault:;
 223
 224         /*
 225          * Find the backing store object and offset into it to begin the
 226          * search.
 227          */
 228         fs.map = map;
 229         if ((result = vm_map_lookup(&fs.map, vaddr,
 230                 fault_type, &fs.entry, &fs.first_object,
 231                 &fs.first_pindex, &prot, &wired)) != KERN_SUCCESS) {
 232                 if ((result != KERN_PROTECTION_FAILURE) ||
 233                         ((fault_flags & VM_FAULT_WIRE_MASK) != VM_FAULT_USER_WIRE)) {
 234                         return result;
 235                 }
 236
 237                 /*
 238                  * If we are user-wiring a r/w segment, and it is COW, then
 239                  * we need to do the COW operation.  Note that we don't COW
 240                  * currently RO sections now, because it is NOT desirable
 241                  * to COW .text.  We simply keep .text from ever being COW'ed
 242                  * and take the heat that one cannot debug wired .text sections.
 243                  */
 244                 result = vm_map_lookup(&fs.map, vaddr,
 245                         VM_PROT_READ|VM_PROT_WRITE|VM_PROT_OVERRIDE_WRITE,
 246                         &fs.entry, &fs.first_object, &fs.first_pindex, &prot, &wired);
 247                 if (result != KERN_SUCCESS) {
 248                         return result;
 249                 }
 250
 251                 /*
 252                  * If we don't COW now, on a user wire, the user will never
 253                  * be able to write to the mapping.  If we don't make this
 254                  * restriction, the bookkeeping would be nearly impossible.
 255                  */
 256                 if ((fs.entry->protection & VM_PROT_WRITE) == 0)
 257                         fs.entry->max_protection &= ~VM_PROT_WRITE;
 258         }
 259
 260         map_generation = fs.map->timestamp;
 261
 262         if (fs.entry->eflags & MAP_ENTRY_NOFAULT) {
 263                 panic("vm_fault: fault on nofault entry, addr: %lx",
 264                     (u_long)vaddr);
 265         }
 266
 267         /*
 268          * Make a reference to this object to prevent its disposal while we
 269          * are messing with it.  Once we have the reference, the map is free
 270          * to be diddled.  Since objects reference their shadows (and copies),
 271          * they will stay around as well.
 272          */
 273         vm_object_reference(fs.first_object);
 274         vm_object_pip_add(fs.first_object, 1);
 275
 276         fs.vp = vnode_pager_lock(fs.first_object);
 277         if ((fault_type & VM_PROT_WRITE) &&
 278                 (fs.first_object->type == OBJT_VNODE)) {
 279                 vm_freeze_copyopts(fs.first_object,
 280                         fs.first_pindex, fs.first_pindex + 1);
 281         }
 282
 283         fs.lookup_still_valid = TRUE;
 284
 285         if (wired)
 286                 fault_type = prot;
 287
 288         fs.first_m = NULL;
 289
 290         /*
 291          * Search for the page at object/offset.
 292          */
 293
 294         fs.object = fs.first_object;
 295         fs.pindex = fs.first_pindex;
 296
 297         while (TRUE) {
 298                 /*
 299                  * If the object is dead, we stop here
 300                  */
 301
 302                 if (fs.object->flags & OBJ_DEAD) {
 303                         unlock_and_deallocate(&fs);
 304                         return (KERN_PROTECTION_FAILURE);
 305                 }
 306
 307                 /*
 308                  * See if page is resident
 309                  */
 310
 311                 fs.m = vm_page_lookup(fs.object, fs.pindex);
 312                 if (fs.m != NULL) {
 313                         int queue, s;
 314                         /*
 315                          * Wait/Retry if the page is busy.  We have to do this
 316                          * if the page is busy via either PG_BUSY or
 317                          * vm_page_t->busy because the vm_pager may be using
 318                          * vm_page_t->busy for pageouts ( and even pageins if
 319                          * it is the vnode pager ), and we could end up trying
 320                          * to pagein and pageout the same page simultaneously.
 321                          *
 322                          * We can theoretically allow the busy case on a read
 323                          * fault if the page is marked valid, but since such
 324                          * pages are typically already pmap'd, putting that
 325                          * special case in might be more effort then it is
 326                          * worth.  We cannot under any circumstances mess
 327                          * around with a vm_page_t->busy page except, perhaps,
 328                          * to pmap it.
 329                          */
 330                         if ((fs.m->flags & PG_BUSY) || fs.m->busy) {
 331                                 unlock_things(&fs);
 332                                 (void)vm_page_sleep_busy(fs.m, TRUE, "vmpfw");
 333                                 cnt.v_intrans++;
 334                                 vm_object_deallocate(fs.first_object);
 335                                 goto RetryFault;
 336                         }
 337
 338                         queue = fs.m->queue;
 339                         s = splvm();
 340                         vm_pageq_remove_nowakeup(fs.m);
 341                         splx(s);
 342
 343                         if ((queue - fs.m->pc) == PQ_CACHE && vm_page_count_severe()) {
 344                                 vm_page_activate(fs.m);
 345                                 unlock_and_deallocate(&fs);
 346                                 VM_WAIT;
 347                                 goto RetryFault;
 348                         }
 349
 350                         /*
 351                          * Mark page busy for other processes, and the
 352                          * pagedaemon.  If it still isn't completely valid
 353                          * (readable), jump to readrest, else break-out ( we
 354                          * found the page ).
 355                          */
 356
 357                         vm_page_busy(fs.m);
 358                         if (((fs.m->valid & VM_PAGE_BITS_ALL) != VM_PAGE_BITS_ALL) &&
 359                                 fs.m->object != kernel_object && fs.m->object != kmem_object) {
 360                                 goto readrest;
 361                         }
 362
 363                         break;
 364                 }
 365
 366                 /*
 367                  * Page is not resident, If this is the search termination
 368                  * or the pager might contain the page, allocate a new page.
 369                  */
 370
 371                 if (TRYPAGER || fs.object == fs.first_object) {
 372                         if (fs.pindex >= fs.object->size) {
 373                                 unlock_and_deallocate(&fs);
 374                                 return (KERN_PROTECTION_FAILURE);
 375                         }
 376
 377                         /*
 378                          * Allocate a new page for this object/offset pair.
 379                          */
 380                         fs.m = NULL;
 381                         if (!vm_page_count_severe()) {
 382                                 fs.m = vm_page_alloc(fs.object, fs.pindex,
 383                                     (fs.vp || fs.object->backing_object)? VM_ALLOC_NORMAL: VM_ALLOC_ZERO);
 384                         }
 385                         if (fs.m == NULL) {
 386                                 unlock_and_deallocate(&fs);
 387                                 VM_WAIT;
 388                                 goto RetryFault;
 389                         }
 390                 }
 391
 392 readrest:
 393                 /*
 394                  * We have found a valid page or we have allocated a new page.
 395                  * The page thus may not be valid or may not be entirely
 396                  * valid.
 397                  *
 398                  * Attempt to fault-in the page if there is a chance that the
 399                  * pager has it, and potentially fault in additional pages
 400                  * at the same time.
 401                  */
 402
 403                 if (TRYPAGER) {
 404                         int rv;
 405                         int reqpage;
 406                         int ahead, behind;
 407                         u_char behavior = vm_map_entry_behavior(fs.entry);
 408
 409                         if (behavior == MAP_ENTRY_BEHAV_RANDOM) {
 410                                 ahead = 0;
 411                                 behind = 0;
 412                         } else {
 413                                 behind = (vaddr - fs.entry->start) >> PAGE_SHIFT;
 414                                 if (behind > VM_FAULT_READ_BEHIND)
 415                                         behind = VM_FAULT_READ_BEHIND;
 416
 417                                 ahead = ((fs.entry->end - vaddr) >> PAGE_SHIFT) - 1;
 418                                 if (ahead > VM_FAULT_READ_AHEAD)
 419                                         ahead = VM_FAULT_READ_AHEAD;
 420                         }
 421
 422                         if ((fs.first_object->type != OBJT_DEVICE) &&
 423                             (behavior == MAP_ENTRY_BEHAV_SEQUENTIAL ||
 424                                 (behavior != MAP_ENTRY_BEHAV_RANDOM &&
 425                                 fs.pindex >= fs.entry->lastr &&
 426                                 fs.pindex < fs.entry->lastr + VM_FAULT_READ))
 427                         ) {
 428                                 vm_pindex_t firstpindex, tmppindex;
 429
 430                                 if (fs.first_pindex < 2 * VM_FAULT_READ)
 431                                         firstpindex = 0;
 432                                 else
 433                                         firstpindex = fs.first_pindex - 2 * VM_FAULT_READ;
 434
 435                                 /*
 436                                  * note: partially valid pages cannot be
 437                                  * included in the lookahead - NFS piecemeal
 438                                  * writes will barf on it badly.
 439                                  */
 440
 441                                 for(tmppindex = fs.first_pindex - 1;
 442                                         tmppindex >= firstpindex;
 443                                         --tmppindex) {
 444                                         vm_page_t mt;
 445                                         mt = vm_page_lookup( fs.first_object, tmppindex);
 446                                         if (mt == NULL || (mt->valid != VM_PAGE_BITS_ALL))
 447                                                 break;
 448                                         if (mt->busy ||
 449                                                 (mt->flags & (PG_BUSY | PG_FICTITIOUS | PG_UNMANAGED)) ||
 450                                                 mt->hold_count ||
 451                                                 mt->wire_count)
 452                                                 continue;
 453                                         if (mt->dirty == 0)
 454                                                 vm_page_test_dirty(mt);
 455                                         if (mt->dirty) {
 456                                                 vm_page_protect(mt, VM_PROT_NONE);
 457                                                 vm_page_deactivate(mt);
 458                                         } else {
 459                                                 vm_page_cache(mt);
 460                                         }
 461                                 }
 462
 463                                 ahead += behind;
 464                                 behind = 0;
 465                         }
 466
 467                         /*
 468                          * now we find out if any other pages should be paged
 469                          * in at this time this routine checks to see if the
 470                          * pages surrounding this fault reside in the same
 471                          * object as the page for this fault.  If they do,
 472                          * then they are faulted in also into the object.  The
 473                          * array "marray" returned contains an array of
 474                          * vm_page_t structs where one of them is the
 475                          * vm_page_t passed to the routine.  The reqpage
 476                          * return value is the index into the marray for the
 477                          * vm_page_t passed to the routine.
 478                          *
 479                          * fs.m plus the additional pages are PG_BUSY'd.
 480                          */
 481                         faultcount = vm_fault_additional_pages(
 482                             fs.m, behind, ahead, marray, &reqpage);
 483
 484                         /*
 485                          * update lastr imperfectly (we do not know how much
 486                          * getpages will actually read), but good enough.
 487                          */
 488                         fs.entry->lastr = fs.pindex + faultcount - behind;
 489
 490                         /*
 491                          * Call the pager to retrieve the data, if any, after
 492                          * releasing the lock on the map.  We hold a ref on
 493                          * fs.object and the pages are PG_BUSY'd.
 494                          */
 495                         unlock_map(&fs);
 496
 497                         rv = faultcount ?
 498                             vm_pager_get_pages(fs.object, marray, faultcount,
 499                                 reqpage) : VM_PAGER_FAIL;
 500
 501                         if (rv == VM_PAGER_OK) {
 502                                 /*
 503                                  * Found the page. Leave it busy while we play
 504                                  * with it.
 505                                  */
 506
 507                                 /*
 508                                  * Relookup in case pager changed page. Pager
 509                                  * is responsible for disposition of old page
 510                                  * if moved.
 511                                  */
 512                                 fs.m = vm_page_lookup(fs.object, fs.pindex);
 513                                 if(!fs.m) {
 514                                         unlock_and_deallocate(&fs);
 515                                         goto RetryFault;
 516                                 }
 517
 518                                 hardfault++;
 519                                 break; /* break to PAGE HAS BEEN FOUND */
 520                         }
 521                         /*
 522                          * Remove the bogus page (which does not exist at this
 523                          * object/offset); before doing so, we must get back
 524                          * our object lock to preserve our invariant.
 525                          *
 526                          * Also wake up any other process that may want to bring
 527                          * in this page.
 528                          *
 529                          * If this is the top-level object, we must leave the
 530                          * busy page to prevent another process from rushing
 531                          * past us, and inserting the page in that object at
 532                          * the same time that we are.
 533                          */
 534
 535                         if (rv == VM_PAGER_ERROR)
 536                                 printf("vm_fault: pager read error, pid %d (%s)\n",
 537                                     curproc->p_pid, curproc->p_comm);
 538                         /*
 539                          * Data outside the range of the pager or an I/O error
 540                          */
 541                         /*
 542                          * XXX - the check for kernel_map is a kludge to work
 543                          * around having the machine panic on a kernel space
 544                          * fault w/ I/O error.
 545                          */
 546                         if (((fs.map != kernel_map) && (rv == VM_PAGER_ERROR)) ||
 547                                 (rv == VM_PAGER_BAD)) {
 548                                 vm_page_free(fs.m);
 549                                 fs.m = NULL;
 550                                 unlock_and_deallocate(&fs);
 551                                 return ((rv == VM_PAGER_ERROR) ? KERN_FAILURE : KERN_PROTECTION_FAILURE);
 552                         }
 553                         if (fs.object != fs.first_object) {
 554                                 vm_page_free(fs.m);
 555                                 fs.m = NULL;
 556                                 /*
 557                                  * XXX - we cannot just fall out at this
 558                                  * point, m has been freed and is invalid!
 559                                  */
 560                         }
 561                 }
 562
 563                 /*
 564                  * We get here if the object has default pager (or unwiring)
 565                  * or the pager doesn't have the page.
 566                  */
 567                 if (fs.object == fs.first_object)
 568                         fs.first_m = fs.m;
 569
 570                 /*
 571                  * Move on to the next object.  Lock the next object before
 572                  * unlocking the current one.
 573                  */
 574
 575                 fs.pindex += OFF_TO_IDX(fs.object->backing_object_offset);
 576                 next_object = fs.object->backing_object;
 577                 if (next_object == NULL) {
 578                         /*
 579                          * If there's no object left, fill the page in the top
 580                          * object with zeros.
 581                          */
 582                         if (fs.object != fs.first_object) {
 583                                 vm_object_pip_wakeup(fs.object);
 584
 585                                 fs.object = fs.first_object;
 586                                 fs.pindex = fs.first_pindex;
 587                                 fs.m = fs.first_m;
 588                         }
 589                         fs.first_m = NULL;
 590
 591                         /*
 592                          * Zero the page if necessary and mark it valid.
 593                          */
 594                         if ((fs.m->flags & PG_ZERO) == 0) {
 595                                 vm_page_zero_fill(fs.m);
 596                         } else {
 597                                 cnt.v_ozfod++;
 598                         }
 599                         cnt.v_zfod++;
 600                         fs.m->valid = VM_PAGE_BITS_ALL;
 601                         break;  /* break to PAGE HAS BEEN FOUND */
 602                 } else {
 603                         if (fs.object != fs.first_object) {
 604                                 vm_object_pip_wakeup(fs.object);
 605                         }
 606                         KASSERT(fs.object != next_object, ("object loop %p", next_object));
 607                         fs.object = next_object;
 608                         vm_object_pip_add(fs.object, 1);
 609                 }
 610         }
 611
 612         KASSERT((fs.m->flags & PG_BUSY) != 0,
 613             ("vm_fault: not busy after main loop"));
 614
 615         /*
 616          * PAGE HAS BEEN FOUND. [Loop invariant still holds -- the object lock
 617          * is held.]
 618          */
 619
 620         /*
 621          * If the page is being written, but isn't already owned by the
 622          * top-level object, we have to copy it into a new page owned by the
 623          * top-level object.
 624          */
 625
 626         if (fs.object != fs.first_object) {
 627                 /*
 628                  * We only really need to copy if we want to write it.
 629                  */
 630
 631                 if (fault_type & VM_PROT_WRITE) {
 632                         /*
 633                          * This allows pages to be virtually copied from a
 634                          * backing_object into the first_object, where the
 635                          * backing object has no other refs to it, and cannot
 636                          * gain any more refs.  Instead of a bcopy, we just
 637                          * move the page from the backing object to the
 638                          * first object.  Note that we must mark the page
 639                          * dirty in the first object so that it will go out
 640                          * to swap when needed.
 641                          */
 642                         if (map_generation == fs.map->timestamp &&
 643                                 /*
 644                                  * Only one shadow object
 645                                  */
 646                                 (fs.object->shadow_count == 1) &&
 647                                 /*
 648                                  * No COW refs, except us
 649                                  */
 650                                 (fs.object->ref_count == 1) &&
 651                                 /*
 652                                  * No one else can look this object up
 653                                  */
 654                                 (fs.object->handle == NULL) &&
 655                                 /*
 656                                  * No other ways to look the object up
 657                                  */
 658                                 ((fs.object->type == OBJT_DEFAULT) ||
 659                                  (fs.object->type == OBJT_SWAP)) &&
 660                                 /*
 661                                  * We don't chase down the shadow chain
 662                                  */
 663                                 (fs.object == fs.first_object->backing_object) &&
 664
 665                                 /*
 666                                  * grab the lock if we need to
 667                                  */
 668                                 (fs.lookup_still_valid ||
 669                                  lockmgr(&fs.map->lock, LK_EXCLUSIVE|LK_NOWAIT, (void *)0, curthread) == 0)
 670                             ) {
 671
 672                                 fs.lookup_still_valid = 1;
 673                                 /*
 674                                  * get rid of the unnecessary page
 675                                  */
 676                                 vm_page_protect(fs.first_m, VM_PROT_NONE);
 677                                 vm_page_free(fs.first_m);
 678                                 fs.first_m = NULL;
 679
 680                                 /*
 681                                  * grab the page and put it into the
 682                                  * process'es object.  The page is
 683                                  * automatically made dirty.
 684                                  */
 685                                 vm_page_rename(fs.m, fs.first_object, fs.first_pindex);
 686                                 fs.first_m = fs.m;
 687                                 vm_page_busy(fs.first_m);
 688                                 fs.m = NULL;
 689                                 cnt.v_cow_optim++;
 690                         } else {
 691                                 /*
 692                                  * Oh, well, lets copy it.
 693                                  */
 694                                 vm_page_copy(fs.m, fs.first_m);
 695                         }
 696
 697                         if (fs.m) {
 698                                 /*
 699                                  * We no longer need the old page or object.
 700                                  */
 701                                 release_page(&fs);
 702                         }
 703
 704                         /*
 705                          * fs.object != fs.first_object due to above
 706                          * conditional
 707                          */
 708
 709                         vm_object_pip_wakeup(fs.object);
 710
 711                         /*
 712                          * Only use the new page below...
 713                          */
 714
 715                         cnt.v_cow_faults++;
 716                         fs.m = fs.first_m;
 717                         fs.object = fs.first_object;
 718                         fs.pindex = fs.first_pindex;
 719
 720                 } else {
 721                         prot &= ~VM_PROT_WRITE;
 722                 }
 723         }
 724
 725         /*
 726          * We must verify that the maps have not changed since our last
 727          * lookup.
 728          */
 729
 730         if (!fs.lookup_still_valid &&
 731                 (fs.map->timestamp != map_generation)) {
 732                 vm_object_t retry_object;
 733                 vm_pindex_t retry_pindex;
 734                 vm_prot_t retry_prot;
 735
 736                 /*
 737                  * Since map entries may be pageable, make sure we can take a
 738                  * page fault on them.
 739                  */
 740
 741                 /*
 742                  * Unlock vnode before the lookup to avoid deadlock.   E.G.
 743                  * avoid a deadlock between the inode and exec_map that can
 744                  * occur due to locks being obtained in different orders.
 745                  */
 746
 747                 if (fs.vp != NULL) {
 748                         vput(fs.vp);
 749                         fs.vp = NULL;
 750                 }
 751
 752                 if (fs.map->infork) {
 753                         release_page(&fs);
 754                         unlock_and_deallocate(&fs);
 755                         goto RetryFault;
 756                 }
 757
 758                 /*
 759                  * To avoid trying to write_lock the map while another process
 760                  * has it read_locked (in vm_map_pageable), we do not try for
 761                  * write permission.  If the page is still writable, we will
 762                  * get write permission.  If it is not, or has been marked
 763                  * needs_copy, we enter the mapping without write permission,
 764                  * and will merely take another fault.
 765                  */
 766                 result = vm_map_lookup(&fs.map, vaddr, fault_type & ~VM_PROT_WRITE,
 767                     &fs.entry, &retry_object, &retry_pindex, &retry_prot, &wired);
 768                 map_generation = fs.map->timestamp;
 769
 770                 /*
 771                  * If we don't need the page any longer, put it on the active
 772                  * list (the easiest thing to do here).  If no one needs it,
 773                  * pageout will grab it eventually.
 774                  */
 775
 776                 if (result != KERN_SUCCESS) {
 777                         release_page(&fs);
 778                         unlock_and_deallocate(&fs);
 779                         return (result);
 780                 }
 781                 fs.lookup_still_valid = TRUE;
 782
 783                 if ((retry_object != fs.first_object) ||
 784                     (retry_pindex != fs.first_pindex)) {
 785                         release_page(&fs);
 786                         unlock_and_deallocate(&fs);
 787                         goto RetryFault;
 788                 }
 789                 /*
 790                  * Check whether the protection has changed or the object has
 791                  * been copied while we left the map unlocked. Changing from
 792                  * read to write permission is OK - we leave the page
 793                  * write-protected, and catch the write fault. Changing from
 794                  * write to read permission means that we can't mark the page
 795                  * write-enabled after all.
 796                  */
 797                 prot &= retry_prot;
 798         }
 799
 800         /*
 801          * Put this page into the physical map. We had to do the unlock above
 802          * because pmap_enter may cause other faults.   We don't put the page
 803          * back on the active queue until later so that the page-out daemon
 804          * won't find us (yet).
 805          */
 806
 807         if (prot & VM_PROT_WRITE) {
 808                 vm_page_flag_set(fs.m, PG_WRITEABLE);
 809                 vm_object_set_flag(fs.m->object,
 810                                    OBJ_WRITEABLE|OBJ_MIGHTBEDIRTY);
 811
 812                 /*
 813                  * If the fault is a write, we know that this page is being
 814                  * written NOW so dirty it explicitly to save on
 815                  * pmap_is_modified() calls later.
 816                  *
 817                  * If this is a NOSYNC mmap we do not want to set PG_NOSYNC
 818                  * if the page is already dirty to prevent data written with
 819                  * the expectation of being synced from not being synced.
 820                  * Likewise if this entry does not request NOSYNC then make
 821                  * sure the page isn't marked NOSYNC.  Applications sharing
 822                  * data should use the same flags to avoid ping ponging.
 823                  *
 824                  * Also tell the backing pager, if any, that it should remove
 825                  * any swap backing since the page is now dirty.
 826                  */
 827                 if (fs.entry->eflags & MAP_ENTRY_NOSYNC) {
 828                         if (fs.m->dirty == 0)
 829                                 vm_page_flag_set(fs.m, PG_NOSYNC);
 830                 } else {
 831                         vm_page_flag_clear(fs.m, PG_NOSYNC);
 832                 }
 833                 if (fault_flags & VM_FAULT_DIRTY) {
 834                         int s;
 835                         vm_page_dirty(fs.m);
 836                         s = splvm();
 837                         vm_pager_page_unswapped(fs.m);
 838                         splx(s);
 839                 }
 840         }
 841
 842         /*
 843          * Page had better still be busy
 844          */
 845
 846         KASSERT(fs.m->flags & PG_BUSY,
 847                 ("vm_fault: page %p not busy!", fs.m));
 848
 849         unlock_things(&fs);
 850
 851         /*
 852          * Sanity check: page must be completely valid or it is not fit to
 853          * map into user space.  vm_pager_get_pages() ensures this.
 854          */
 855
 856         if (fs.m->valid != VM_PAGE_BITS_ALL) {
 857                 vm_page_zero_invalid(fs.m, TRUE);
 858                 printf("Warning: page %p partially invalid on fault\n", fs.m);
 859         }
 860
 861         pmap_enter(fs.map->pmap, vaddr, fs.m, prot, wired);
 862
 863         if (((fault_flags & VM_FAULT_WIRE_MASK) == 0) && (wired == 0)) {
 864                 pmap_prefault(fs.map->pmap, vaddr, fs.entry);
 865         }
 866
 867         vm_page_flag_clear(fs.m, PG_ZERO);
 868         vm_page_flag_set(fs.m, PG_MAPPED|PG_REFERENCED);
 869         if (fault_flags & VM_FAULT_HOLD)
 870                 vm_page_hold(fs.m);
 871
 872         /*
 873          * If the page is not wired down, then put it where the pageout daemon
 874          * can find it.
 875          */
 876
 877         if (fault_flags & VM_FAULT_WIRE_MASK) {
 878                 if (wired)
 879                         vm_page_wire(fs.m);
 880                 else
 881                         vm_page_unwire(fs.m, 1);
 882         } else {
 883                 vm_page_activate(fs.m);
 884         }
 885
 886         mtx_lock_spin(&sched_lock);
 887         if (curproc && (curproc->p_sflag & PS_INMEM) && curproc->p_stats) {
 888                 if (hardfault) {
 889                         curproc->p_stats->p_ru.ru_majflt++;
 890                 } else {
 891                         curproc->p_stats->p_ru.ru_minflt++;
 892                 }
 893         }
 894         mtx_unlock_spin(&sched_lock);
 895
 896         /*
 897          * Unlock everything, and return
 898          */
 899
 900         vm_page_wakeup(fs.m);
 901         vm_object_deallocate(fs.first_object);
 902
 903         return (KERN_SUCCESS);
 904
 905 }
 906
 907 /*
 908  *      vm_fault_wire:
 909  *
 910  *      Wire down a range of virtual addresses in a map.
 911  */
 912 int
 913 vm_fault_wire(map, start, end)
 914         vm_map_t map;
 915         vm_offset_t start, end;
 916 {
 917
 918         vm_offset_t va;
 919         pmap_t pmap;
 920         int rv;
 921
 922         pmap = vm_map_pmap(map);
 923
 924         /*
 925          * Inform the physical mapping system that the range of addresses may
 926          * not fault, so that page tables and such can be locked down as well.
 927          */
 928
 929         pmap_pageable(pmap, start, end, FALSE);
 930
 931         /*
 932          * We simulate a fault to get the page and enter it in the physical
 933          * map.
 934          */
 935
 936         for (va = start; va < end; va += PAGE_SIZE) {
 937                 rv = vm_fault(map, va, VM_PROT_READ|VM_PROT_WRITE,
 938                         VM_FAULT_CHANGE_WIRING);
 939                 if (rv) {
 940                         if (va != start)
 941                                 vm_fault_unwire(map, start, va);
 942                         return (rv);
 943                 }
 944         }
 945         return (KERN_SUCCESS);
 946 }
 947
 948 /*
 949  *      vm_fault_user_wire:
 950  *
 951  *      Wire down a range of virtual addresses in a map.  This
 952  *      is for user mode though, so we only ask for read access
 953  *      on currently read only sections.
 954  */
 955 int
 956 vm_fault_user_wire(map, start, end)
 957         vm_map_t map;
 958         vm_offset_t start, end;
 959 {
 960
 961         vm_offset_t va;
 962         pmap_t pmap;
 963         int rv;
 964
 965         GIANT_REQUIRED;
 966
 967         pmap = vm_map_pmap(map);
 968
 969         /*
 970          * Inform the physical mapping system that the range of addresses may
 971          * not fault, so that page tables and such can be locked down as well.
 972          */
 973
 974         pmap_pageable(pmap, start, end, FALSE);
 975
 976         /*
 977          * We simulate a fault to get the page and enter it in the physical
 978          * map.
 979          */
 980         for (va = start; va < end; va += PAGE_SIZE) {
 981                 rv = vm_fault(map, va, VM_PROT_READ, VM_FAULT_USER_WIRE);
 982                 if (rv) {
 983                         if (va != start)
 984                                 vm_fault_unwire(map, start, va);
 985                         return (rv);
 986                 }
 987         }
 988         return (KERN_SUCCESS);
 989 }
 990
 991
 992 /*
 993  *      vm_fault_unwire:
 994  *
 995  *      Unwire a range of virtual addresses in a map.
 996  */
 997 void
 998 vm_fault_unwire(map, start, end)
 999         vm_map_t map;
1000         vm_offset_t start, end;
1001 {
1002
1003         vm_offset_t va, pa;
1004         pmap_t pmap;
1005
1006         pmap = vm_map_pmap(map);
1007
1008         /*
1009          * Since the pages are wired down, we must be able to get their
1010          * mappings from the physical map system.
1011          */
1012
1013         for (va = start; va < end; va += PAGE_SIZE) {
1014                 pa = pmap_extract(pmap, va);
1015                 if (pa != (vm_offset_t) 0) {
1016                         pmap_change_wiring(pmap, va, FALSE);
1017                         vm_page_unwire(PHYS_TO_VM_PAGE(pa), 1);
1018                 }
1019         }
1020
1021         /*
1022          * Inform the physical mapping system that the range of addresses may
1023          * fault, so that page tables and such may be unwired themselves.
1024          */
1025
1026         pmap_pageable(pmap, start, end, TRUE);
1027
1028 }
1029
1030 /*
1031  *      Routine:
1032  *              vm_fault_copy_entry
1033  *      Function:
1034  *              Copy all of the pages from a wired-down map entry to another.
1035  *
1036  *      In/out conditions:
1037  *              The source and destination maps must be locked for write.
1038  *              The source map entry must be wired down (or be a sharing map
1039  *              entry corresponding to a main map entry that is wired down).
1040  */
1041
1042 void
1043 vm_fault_copy_entry(dst_map, src_map, dst_entry, src_entry)
1044         vm_map_t dst_map;
1045         vm_map_t src_map;
1046         vm_map_entry_t dst_entry;
1047         vm_map_entry_t src_entry;
1048 {
1049         vm_object_t dst_object;
1050         vm_object_t src_object;
1051         vm_ooffset_t dst_offset;
1052         vm_ooffset_t src_offset;
1053         vm_prot_t prot;
1054         vm_offset_t vaddr;
1055         vm_page_t dst_m;
1056         vm_page_t src_m;
1057
1058 #ifdef  lint
1059         src_map++;
1060 #endif  /* lint */
1061
1062         src_object = src_entry->object.vm_object;
1063         src_offset = src_entry->offset;
1064
1065         /*
1066          * Create the top-level object for the destination entry. (Doesn't
1067          * actually shadow anything - we copy the pages directly.)
1068          */
1069         dst_object = vm_object_allocate(OBJT_DEFAULT,
1070             (vm_size_t) OFF_TO_IDX(dst_entry->end - dst_entry->start));
1071
1072         dst_entry->object.vm_object = dst_object;
1073         dst_entry->offset = 0;
1074
1075         prot = dst_entry->max_protection;
1076
1077         /*
1078          * Loop through all of the pages in the entry's range, copying each
1079          * one from the source object (it should be there) to the destination
1080          * object.
1081          */
1082         for (vaddr = dst_entry->start, dst_offset = 0;
1083             vaddr < dst_entry->end;
1084             vaddr += PAGE_SIZE, dst_offset += PAGE_SIZE) {
1085
1086                 /*
1087                  * Allocate a page in the destination object
1088                  */
1089                 do {
1090                         dst_m = vm_page_alloc(dst_object,
1091                                 OFF_TO_IDX(dst_offset), VM_ALLOC_NORMAL);
1092                         if (dst_m == NULL) {
1093                                 VM_WAIT;
1094                         }
1095                 } while (dst_m == NULL);
1096
1097                 /*
1098                  * Find the page in the source object, and copy it in.
1099                  * (Because the source is wired down, the page will be in
1100                  * memory.)
1101                  */
1102                 src_m = vm_page_lookup(src_object,
1103                         OFF_TO_IDX(dst_offset + src_offset));
1104                 if (src_m == NULL)
1105                         panic("vm_fault_copy_wired: page missing");
1106
1107                 vm_page_copy(src_m, dst_m);
1108
1109                 /*
1110                  * Enter it in the pmap...
1111                  */
1112
1113                 vm_page_flag_clear(dst_m, PG_ZERO);
1114                 pmap_enter(dst_map->pmap, vaddr, dst_m, prot, FALSE);
1115                 vm_page_flag_set(dst_m, PG_WRITEABLE|PG_MAPPED);
1116
1117                 /*
1118                  * Mark it no longer busy, and put it on the active list.
1119                  */
1120                 vm_page_activate(dst_m);
1121                 vm_page_wakeup(dst_m);
1122         }
1123 }
1124
1125
1126 /*
1127  * This routine checks around the requested page for other pages that
1128  * might be able to be faulted in.  This routine brackets the viable
1129  * pages for the pages to be paged in.
1130  *
1131  * Inputs:
1132  *      m, rbehind, rahead
1133  *
1134  * Outputs:
1135  *  marray (array of vm_page_t), reqpage (index of requested page)
1136  *
1137  * Return value:
1138  *  number of pages in marray
1139  *
1140  * This routine can't block.
1141  */
1142 static int
1143 vm_fault_additional_pages(m, rbehind, rahead, marray, reqpage)
1144         vm_page_t m;
1145         int rbehind;
1146         int rahead;
1147         vm_page_t *marray;
1148         int *reqpage;
1149 {
1150         int i,j;
1151         vm_object_t object;
1152         vm_pindex_t pindex, startpindex, endpindex, tpindex;
1153         vm_page_t rtm;
1154         int cbehind, cahead;
1155
1156         GIANT_REQUIRED;
1157
1158         object = m->object;
1159         pindex = m->pindex;
1160
1161         /*
1162          * we don't fault-ahead for device pager
1163          */
1164         if (object->type == OBJT_DEVICE) {
1165                 *reqpage = 0;
1166                 marray[0] = m;
1167                 return 1;
1168         }
1169
1170         /*
1171          * if the requested page is not available, then give up now
1172          */
1173
1174         if (!vm_pager_has_page(object, pindex, &cbehind, &cahead)) {
1175                 return 0;
1176         }
1177
1178         if ((cbehind == 0) && (cahead == 0)) {
1179                 *reqpage = 0;
1180                 marray[0] = m;
1181                 return 1;
1182         }
1183
1184         if (rahead > cahead) {
1185                 rahead = cahead;
1186         }
1187
1188         if (rbehind > cbehind) {
1189                 rbehind = cbehind;
1190         }
1191
1192         /*
1193          * try to do any readahead that we might have free pages for.
1194          */
1195         if ((rahead + rbehind) >
1196                 ((cnt.v_free_count + cnt.v_cache_count) - cnt.v_free_reserved)) {
1197                 pagedaemon_wakeup();
1198                 marray[0] = m;
1199                 *reqpage = 0;
1200                 return 1;
1201         }
1202
1203         /*
1204          * scan backward for the read behind pages -- in memory
1205          */
1206         if (pindex > 0) {
1207                 if (rbehind > pindex) {
1208                         rbehind = pindex;
1209                         startpindex = 0;
1210                 } else {
1211                         startpindex = pindex - rbehind;
1212                 }
1213
1214                 for ( tpindex = pindex - 1; tpindex >= startpindex; tpindex -= 1) {
1215                         if (vm_page_lookup( object, tpindex)) {
1216                                 startpindex = tpindex + 1;
1217                                 break;
1218                         }
1219                         if (tpindex == 0)
1220                                 break;
1221                 }
1222
1223                 for(i = 0, tpindex = startpindex; tpindex < pindex; i++, tpindex++) {
1224
1225                         rtm = vm_page_alloc(object, tpindex, VM_ALLOC_NORMAL);
1226                         if (rtm == NULL) {
1227                                 for (j = 0; j < i; j++) {
1228                                         vm_page_free(marray[j]);
1229                                 }
1230                                 marray[0] = m;
1231                                 *reqpage = 0;
1232                                 return 1;
1233                         }
1234
1235                         marray[i] = rtm;
1236                 }
1237         } else {
1238                 startpindex = 0;
1239                 i = 0;
1240         }
1241
1242         marray[i] = m;
1243         /* page offset of the required page */
1244         *reqpage = i;
1245
1246         tpindex = pindex + 1;
1247         i++;
1248
1249         /*
1250          * scan forward for the read ahead pages
1251          */
1252         endpindex = tpindex + rahead;
1253         if (endpindex > object->size)
1254                 endpindex = object->size;
1255
1256         for( ; tpindex < endpindex; i++, tpindex++) {
1257
1258                 if (vm_page_lookup(object, tpindex)) {
1259                         break;
1260                 }
1261
1262                 rtm = vm_page_alloc(object, tpindex, VM_ALLOC_NORMAL);
1263                 if (rtm == NULL) {
1264                         break;
1265                 }
1266
1267                 marray[i] = rtm;
1268         }
1269
1270         /* return number of bytes of pages */
1271         return i;
1272 }