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: src/sys/vm/vm_fault.c,v 1.108.2.8 2002/02/26 05:49:27 silby Exp $
  70  * $DragonFly: src/sys/vm/vm_fault.c,v 1.47 2008/07/01 02:02:56 dillon Exp $
  71  */
  72
  73 /*
  74  *      Page fault handling module.
  75  */
  76
  77 #include <sys/param.h>
  78 #include <sys/systm.h>
  79 #include <sys/kernel.h>
  80 #include <sys/proc.h>
  81 #include <sys/vnode.h>
  82 #include <sys/resourcevar.h>
  83 #include <sys/vmmeter.h>
  84 #include <sys/vkernel.h>
  85 #include <sys/sfbuf.h>
  86 #include <sys/lock.h>
  87 #include <sys/sysctl.h>
  88
  89 #include <vm/vm.h>
  90 #include <vm/vm_param.h>
  91 #include <vm/pmap.h>
  92 #include <vm/vm_map.h>
  93 #include <vm/vm_object.h>
  94 #include <vm/vm_page.h>
  95 #include <vm/vm_pageout.h>
  96 #include <vm/vm_kern.h>
  97 #include <vm/vm_pager.h>
  98 #include <vm/vnode_pager.h>
  99 #include <vm/vm_extern.h>
 100
 101 #include <sys/thread2.h>
 102 #include <vm/vm_page2.h>
 103
 104 struct faultstate {
 105         vm_page_t m;
 106         vm_object_t object;
 107         vm_pindex_t pindex;
 108         vm_prot_t prot;
 109         vm_page_t first_m;
 110         vm_object_t first_object;
 111         vm_prot_t first_prot;
 112         vm_map_t map;
 113         vm_map_entry_t entry;
 114         int lookup_still_valid;
 115         int didlimit;
 116         int hardfault;
 117         int fault_flags;
 118         int map_generation;
 119         boolean_t wired;
 120         struct vnode *vp;
 121 };
 122
 123 static int vm_fast_fault = 1;
 124 SYSCTL_INT(_vm, OID_AUTO, fast_fault, CTLFLAG_RW, &vm_fast_fault, 0, "");
 125 static int debug_cluster = 0;
 126 SYSCTL_INT(_vm, OID_AUTO, debug_cluster, CTLFLAG_RW, &debug_cluster, 0, "");
 127
 128 static int vm_fault_object(struct faultstate *, vm_pindex_t, vm_prot_t);
 129 static int vm_fault_vpagetable(struct faultstate *, vm_pindex_t *, vpte_t, int);
 130 #if 0
 131 static int vm_fault_additional_pages (vm_page_t, int, int, vm_page_t *, int *);
 132 #endif
 133 static int vm_fault_ratelimit(struct vmspace *);
 134 static void vm_prefault(pmap_t pmap, vm_offset_t addra, vm_map_entry_t entry,
 135                         int prot);
 136
 137 static __inline void
 138 release_page(struct faultstate *fs)
 139 {
 140         vm_page_deactivate(fs->m);
 141         vm_page_wakeup(fs->m);
 142         fs->m = NULL;
 143 }
 144
 145 static __inline void
 146 unlock_map(struct faultstate *fs)
 147 {
 148         if (fs->lookup_still_valid && fs->map) {
 149                 vm_map_lookup_done(fs->map, fs->entry, 0);
 150                 fs->lookup_still_valid = FALSE;
 151         }
 152 }
 153
 154 /*
 155  * Clean up after a successful call to vm_fault_object() so another call
 156  * to vm_fault_object() can be made.
 157  */
 158 static void
 159 _cleanup_successful_fault(struct faultstate *fs, int relock)
 160 {
 161         if (fs->object != fs->first_object) {
 162                 vm_page_free(fs->first_m);
 163                 vm_object_pip_wakeup(fs->object);
 164                 fs->first_m = NULL;
 165         }
 166         fs->object = fs->first_object;
 167         if (relock && fs->lookup_still_valid == FALSE) {
 168                 if (fs->map)
 169                         vm_map_lock_read(fs->map);
 170                 fs->lookup_still_valid = TRUE;
 171         }
 172 }
 173
 174 static void
 175 _unlock_things(struct faultstate *fs, int dealloc)
 176 {
 177         vm_object_pip_wakeup(fs->first_object);
 178         _cleanup_successful_fault(fs, 0);
 179         if (dealloc) {
 180                 vm_object_deallocate(fs->first_object);
 181                 fs->first_object = NULL;
 182         }
 183         unlock_map(fs);
 184         if (fs->vp != NULL) {
 185                 vput(fs->vp);
 186                 fs->vp = NULL;
 187         }
 188 }
 189
 190 #define unlock_things(fs) _unlock_things(fs, 0)
 191 #define unlock_and_deallocate(fs) _unlock_things(fs, 1)
 192 #define cleanup_successful_fault(fs) _cleanup_successful_fault(fs, 1)
 193
 194 /*
 195  * TRYPAGER
 196  *
 197  * Determine if the pager for the current object *might* contain the page.
 198  *
 199  * We only need to try the pager if this is not a default object (default
 200  * objects are zero-fill and have no real pager), and if we are not taking
 201  * a wiring fault or if the FS entry is wired.
 202  */
 203 #define TRYPAGER(fs)    \
 204                 (fs->object->type != OBJT_DEFAULT && \
 205                 (((fs->fault_flags & VM_FAULT_WIRE_MASK) == 0) || fs->wired))
 206
 207 /*
 208  * vm_fault:
 209  *
 210  * Handle a page fault occuring at the given address, requiring the given
 211  * permissions, in the map specified.  If successful, the page is inserted
 212  * into the associated physical map.
 213  *
 214  * NOTE: The given address should be truncated to the proper page address.
 215  *
 216  * KERN_SUCCESS is returned if the page fault is handled; otherwise,
 217  * a standard error specifying why the fault is fatal is returned.
 218  *
 219  * The map in question must be referenced, and remains so.
 220  * The caller may hold no locks.
 221  */
 222 int
 223 vm_fault(vm_map_t map, vm_offset_t vaddr, vm_prot_t fault_type, int fault_flags)
 224 {
 225         int result;
 226         vm_pindex_t first_pindex;
 227         struct faultstate fs;
 228
 229         mycpu->gd_cnt.v_vm_faults++;
 230
 231         fs.didlimit = 0;
 232         fs.hardfault = 0;
 233         fs.fault_flags = fault_flags;
 234
 235 RetryFault:
 236         /*
 237          * Find the vm_map_entry representing the backing store and resolve
 238          * the top level object and page index.  This may have the side
 239          * effect of executing a copy-on-write on the map entry and/or
 240          * creating a shadow object, but will not COW any actual VM pages.
 241          *
 242          * On success fs.map is left read-locked and various other fields
 243          * are initialized but not otherwise referenced or locked.
 244          *
 245          * NOTE!  vm_map_lookup will try to upgrade the fault_type to
 246          * VM_FAULT_WRITE if the map entry is a virtual page table and also
 247          * writable, so we can set the 'A'accessed bit in the virtual page
 248          * table entry.
 249          */
 250         fs.map = map;
 251         result = vm_map_lookup(&fs.map, vaddr, fault_type,
 252                                &fs.entry, &fs.first_object,
 253                                &first_pindex, &fs.first_prot, &fs.wired);
 254
 255         /*
 256          * If the lookup failed or the map protections are incompatible,
 257          * the fault generally fails.  However, if the caller is trying
 258          * to do a user wiring we have more work to do.
 259          */
 260         if (result != KERN_SUCCESS) {
 261                 if (result != KERN_PROTECTION_FAILURE)
 262                         return result;
 263                 if ((fs.fault_flags & VM_FAULT_WIRE_MASK) != VM_FAULT_USER_WIRE)
 264                         return result;
 265
 266                 /*
 267                  * If we are user-wiring a r/w segment, and it is COW, then
 268                  * we need to do the COW operation.  Note that we don't
 269                  * currently COW RO sections now, because it is NOT desirable
 270                  * to COW .text.  We simply keep .text from ever being COW'ed
 271                  * and take the heat that one cannot debug wired .text sections.
 272                  */
 273                 result = vm_map_lookup(&fs.map, vaddr,
 274                                        VM_PROT_READ|VM_PROT_WRITE|
 275                                         VM_PROT_OVERRIDE_WRITE,
 276                                        &fs.entry, &fs.first_object,
 277                                        &first_pindex, &fs.first_prot,
 278                                        &fs.wired);
 279                 if (result != KERN_SUCCESS)
 280                         return result;
 281
 282                 /*
 283                  * If we don't COW now, on a user wire, the user will never
 284                  * be able to write to the mapping.  If we don't make this
 285                  * restriction, the bookkeeping would be nearly impossible.
 286                  */
 287                 if ((fs.entry->protection & VM_PROT_WRITE) == 0)
 288                         fs.entry->max_protection &= ~VM_PROT_WRITE;
 289         }
 290
 291         /*
 292          * fs.map is read-locked
 293          *
 294          * Misc checks.  Save the map generation number to detect races.
 295          */
 296         fs.map_generation = fs.map->timestamp;
 297
 298         if (fs.entry->eflags & MAP_ENTRY_NOFAULT) {
 299                 panic("vm_fault: fault on nofault entry, addr: %lx",
 300                     (u_long)vaddr);
 301         }
 302
 303         /*
 304          * A system map entry may return a NULL object.  No object means
 305          * no pager means an unrecoverable kernel fault.
 306          */
 307         if (fs.first_object == NULL) {
 308                 panic("vm_fault: unrecoverable fault at %p in entry %p",
 309                         (void *)vaddr, fs.entry);
 310         }
 311
 312         /*
 313          * Make a reference to this object to prevent its disposal while we
 314          * are messing with it.  Once we have the reference, the map is free
 315          * to be diddled.  Since objects reference their shadows (and copies),
 316          * they will stay around as well.
 317          *
 318          * Bump the paging-in-progress count to prevent size changes (e.g.
 319          * truncation operations) during I/O.  This must be done after
 320          * obtaining the vnode lock in order to avoid possible deadlocks.
 321          */
 322         vm_object_reference(fs.first_object);
 323         fs.vp = vnode_pager_lock(fs.first_object);
 324         vm_object_pip_add(fs.first_object, 1);
 325
 326         fs.lookup_still_valid = TRUE;
 327         fs.first_m = NULL;
 328         fs.object = fs.first_object;    /* so unlock_and_deallocate works */
 329
 330         /*
 331          * If the entry is wired we cannot change the page protection.
 332          */
 333         if (fs.wired)
 334                 fault_type = fs.first_prot;
 335
 336         /*
 337          * The page we want is at (first_object, first_pindex), but if the
 338          * vm_map_entry is VM_MAPTYPE_VPAGETABLE we have to traverse the
 339          * page table to figure out the actual pindex.
 340          *
 341          * NOTE!  DEVELOPMENT IN PROGRESS, THIS IS AN INITIAL IMPLEMENTATION
 342          * ONLY
 343          */
 344         if (fs.entry->maptype == VM_MAPTYPE_VPAGETABLE) {
 345                 result = vm_fault_vpagetable(&fs, &first_pindex,
 346                                              fs.entry->aux.master_pde,
 347                                              fault_type);
 348                 if (result == KERN_TRY_AGAIN)
 349                         goto RetryFault;
 350                 if (result != KERN_SUCCESS)
 351                         return (result);
 352         }
 353
 354         /*
 355          * Now we have the actual (object, pindex), fault in the page.  If
 356          * vm_fault_object() fails it will unlock and deallocate the FS
 357          * data.   If it succeeds everything remains locked and fs->object
 358          * will have an additinal PIP count if it is not equal to
 359          * fs->first_object
 360          *
 361          * vm_fault_object will set fs->prot for the pmap operation.  It is
 362          * allowed to set VM_PROT_WRITE if fault_type == VM_PROT_READ if the
 363          * page can be safely written.  However, it will force a read-only
 364          * mapping for a read fault if the memory is managed by a virtual
 365          * page table.
 366          */
 367         result = vm_fault_object(&fs, first_pindex, fault_type);
 368
 369         if (result == KERN_TRY_AGAIN)
 370                 goto RetryFault;
 371         if (result != KERN_SUCCESS)
 372                 return (result);
 373
 374         /*
 375          * On success vm_fault_object() does not unlock or deallocate, and fs.m
 376          * will contain a busied page.
 377          *
 378          * Enter the page into the pmap and do pmap-related adjustments.
 379          */
 380         pmap_enter(fs.map->pmap, vaddr, fs.m, fs.prot, fs.wired);
 381
 382         /*
 383          * Burst in a few more pages if possible.  The fs.map should still
 384          * be locked.
 385          */
 386         if (fault_flags & VM_FAULT_BURST) {
 387                 if ((fs.fault_flags & VM_FAULT_WIRE_MASK) == 0 &&
 388                     fs.wired == 0) {
 389                         vm_prefault(fs.map->pmap, vaddr, fs.entry, fs.prot);
 390                 }
 391         }
 392         unlock_things(&fs);
 393
 394         vm_page_flag_clear(fs.m, PG_ZERO);
 395         vm_page_flag_set(fs.m, PG_REFERENCED);
 396
 397         /*
 398          * If the page is not wired down, then put it where the pageout daemon
 399          * can find it.
 400          */
 401         if (fs.fault_flags & VM_FAULT_WIRE_MASK) {
 402                 if (fs.wired)
 403                         vm_page_wire(fs.m);
 404                 else
 405                         vm_page_unwire(fs.m, 1);
 406         } else {
 407                 vm_page_activate(fs.m);
 408         }
 409
 410         if (curthread->td_lwp) {
 411                 if (fs.hardfault) {
 412                         curthread->td_lwp->lwp_ru.ru_majflt++;
 413                 } else {
 414                         curthread->td_lwp->lwp_ru.ru_minflt++;
 415                 }
 416         }
 417
 418         /*
 419          * Unlock everything, and return
 420          */
 421         vm_page_wakeup(fs.m);
 422         vm_object_deallocate(fs.first_object);
 423
 424         return (KERN_SUCCESS);
 425 }
 426
 427 /*
 428  * Fault in the specified virtual address in the current process map,
 429  * returning a held VM page or NULL.  See vm_fault_page() for more
 430  * information.
 431  */
 432 vm_page_t
 433 vm_fault_page_quick(vm_offset_t va, vm_prot_t fault_type, int *errorp)
 434 {
 435         struct lwp *lp = curthread->td_lwp;
 436         vm_page_t m;
 437
 438         m = vm_fault_page(&lp->lwp_vmspace->vm_map, va,
 439                           fault_type, VM_FAULT_NORMAL, errorp);
 440         return(m);
 441 }
 442
 443 /*
 444  * Fault in the specified virtual address in the specified map, doing all
 445  * necessary manipulation of the object store and all necessary I/O.  Return
 446  * a held VM page or NULL, and set *errorp.  The related pmap is not
 447  * updated.
 448  *
 449  * The returned page will be properly dirtied if VM_PROT_WRITE was specified,
 450  * and marked PG_REFERENCED as well.
 451  *
 452  * If the page cannot be faulted writable and VM_PROT_WRITE was specified, an
 453  * error will be returned.
 454  */
 455 vm_page_t
 456 vm_fault_page(vm_map_t map, vm_offset_t vaddr, vm_prot_t fault_type,
 457               int fault_flags, int *errorp)
 458 {
 459         vm_pindex_t first_pindex;
 460         struct faultstate fs;
 461         int result;
 462         vm_prot_t orig_fault_type = fault_type;
 463
 464         mycpu->gd_cnt.v_vm_faults++;
 465
 466         fs.didlimit = 0;
 467         fs.hardfault = 0;
 468         fs.fault_flags = fault_flags;
 469         KKASSERT((fault_flags & VM_FAULT_WIRE_MASK) == 0);
 470
 471 RetryFault:
 472         /*
 473          * Find the vm_map_entry representing the backing store and resolve
 474          * the top level object and page index.  This may have the side
 475          * effect of executing a copy-on-write on the map entry and/or
 476          * creating a shadow object, but will not COW any actual VM pages.
 477          *
 478          * On success fs.map is left read-locked and various other fields
 479          * are initialized but not otherwise referenced or locked.
 480          *
 481          * NOTE!  vm_map_lookup will upgrade the fault_type to VM_FAULT_WRITE
 482          * if the map entry is a virtual page table and also writable,
 483          * so we can set the 'A'accessed bit in the virtual page table entry.
 484          */
 485         fs.map = map;
 486         result = vm_map_lookup(&fs.map, vaddr, fault_type,
 487                                &fs.entry, &fs.first_object,
 488                                &first_pindex, &fs.first_prot, &fs.wired);
 489
 490         if (result != KERN_SUCCESS) {
 491                 *errorp = result;
 492                 return (NULL);
 493         }
 494
 495         /*
 496          * fs.map is read-locked
 497          *
 498          * Misc checks.  Save the map generation number to detect races.
 499          */
 500         fs.map_generation = fs.map->timestamp;
 501
 502         if (fs.entry->eflags & MAP_ENTRY_NOFAULT) {
 503                 panic("vm_fault: fault on nofault entry, addr: %lx",
 504                     (u_long)vaddr);
 505         }
 506
 507         /*
 508          * A system map entry may return a NULL object.  No object means
 509          * no pager means an unrecoverable kernel fault.
 510          */
 511         if (fs.first_object == NULL) {
 512                 panic("vm_fault: unrecoverable fault at %p in entry %p",
 513                         (void *)vaddr, fs.entry);
 514         }
 515
 516         /*
 517          * Make a reference to this object to prevent its disposal while we
 518          * are messing with it.  Once we have the reference, the map is free
 519          * to be diddled.  Since objects reference their shadows (and copies),
 520          * they will stay around as well.
 521          *
 522          * Bump the paging-in-progress count to prevent size changes (e.g.
 523          * truncation operations) during I/O.  This must be done after
 524          * obtaining the vnode lock in order to avoid possible deadlocks.
 525          */
 526         vm_object_reference(fs.first_object);
 527         fs.vp = vnode_pager_lock(fs.first_object);
 528         vm_object_pip_add(fs.first_object, 1);
 529
 530         fs.lookup_still_valid = TRUE;
 531         fs.first_m = NULL;
 532         fs.object = fs.first_object;    /* so unlock_and_deallocate works */
 533
 534         /*
 535          * If the entry is wired we cannot change the page protection.
 536          */
 537         if (fs.wired)
 538                 fault_type = fs.first_prot;
 539
 540         /*
 541          * The page we want is at (first_object, first_pindex), but if the
 542          * vm_map_entry is VM_MAPTYPE_VPAGETABLE we have to traverse the
 543          * page table to figure out the actual pindex.
 544          *
 545          * NOTE!  DEVELOPMENT IN PROGRESS, THIS IS AN INITIAL IMPLEMENTATION
 546          * ONLY
 547          */
 548         if (fs.entry->maptype == VM_MAPTYPE_VPAGETABLE) {
 549                 result = vm_fault_vpagetable(&fs, &first_pindex,
 550                                              fs.entry->aux.master_pde,
 551                                              fault_type);
 552                 if (result == KERN_TRY_AGAIN)
 553                         goto RetryFault;
 554                 if (result != KERN_SUCCESS) {
 555                         *errorp = result;
 556                         return (NULL);
 557                 }
 558         }
 559
 560         /*
 561          * Now we have the actual (object, pindex), fault in the page.  If
 562          * vm_fault_object() fails it will unlock and deallocate the FS
 563          * data.   If it succeeds everything remains locked and fs->object
 564          * will have an additinal PIP count if it is not equal to
 565          * fs->first_object
 566          */
 567         result = vm_fault_object(&fs, first_pindex, fault_type);
 568
 569         if (result == KERN_TRY_AGAIN)
 570                 goto RetryFault;
 571         if (result != KERN_SUCCESS) {
 572                 *errorp = result;
 573                 return(NULL);
 574         }
 575
 576         if ((orig_fault_type & VM_PROT_WRITE) &&
 577             (fs.prot & VM_PROT_WRITE) == 0) {
 578                 *errorp = KERN_PROTECTION_FAILURE;
 579                 unlock_and_deallocate(&fs);
 580                 return(NULL);
 581         }
 582
 583         /*
 584          * On success vm_fault_object() does not unlock or deallocate, and fs.m
 585          * will contain a busied page.
 586          */
 587         unlock_things(&fs);
 588
 589         /*
 590          * Return a held page.  We are not doing any pmap manipulation so do
 591          * not set PG_MAPPED.  However, adjust the page flags according to
 592          * the fault type because the caller may not use a managed pmapping
 593          * (so we don't want to lose the fact that the page will be dirtied
 594          * if a write fault was specified).
 595          */
 596         vm_page_hold(fs.m);
 597         vm_page_flag_clear(fs.m, PG_ZERO);
 598         if (fault_type & VM_PROT_WRITE)
 599                 vm_page_dirty(fs.m);
 600
 601         /*
 602          * Update the pmap.  We really only have to do this if a COW
 603          * occured to replace the read-only page with the new page.  For
 604          * now just do it unconditionally. XXX
 605          */
 606         pmap_enter(fs.map->pmap, vaddr, fs.m, fs.prot, fs.wired);
 607         vm_page_flag_set(fs.m, PG_REFERENCED);
 608
 609         /*
 610          * Unbusy the page by activating it.  It remains held and will not
 611          * be reclaimed.
 612          */
 613         vm_page_activate(fs.m);
 614
 615         if (curthread->td_lwp) {
 616                 if (fs.hardfault) {
 617                         curthread->td_lwp->lwp_ru.ru_majflt++;
 618                 } else {
 619                         curthread->td_lwp->lwp_ru.ru_minflt++;
 620                 }
 621         }
 622
 623         /*
 624          * Unlock everything, and return the held page.
 625          */
 626         vm_page_wakeup(fs.m);
 627         vm_object_deallocate(fs.first_object);
 628
 629         *errorp = 0;
 630         return(fs.m);
 631 }
 632
 633 /*
 634  * Fault in the specified (object,offset), dirty the returned page as
 635  * needed.  If the requested fault_type cannot be done NULL and an
 636  * error is returned.
 637  */
 638 vm_page_t
 639 vm_fault_object_page(vm_object_t object, vm_ooffset_t offset,
 640                      vm_prot_t fault_type, int fault_flags, int *errorp)
 641 {
 642         int result;
 643         vm_pindex_t first_pindex;
 644         struct faultstate fs;
 645         struct vm_map_entry entry;
 646
 647         bzero(&entry, sizeof(entry));
 648         entry.object.vm_object = object;
 649         entry.maptype = VM_MAPTYPE_NORMAL;
 650         entry.protection = entry.max_protection = fault_type;
 651
 652         fs.didlimit = 0;
 653         fs.hardfault = 0;
 654         fs.fault_flags = fault_flags;
 655         fs.map = NULL;
 656         KKASSERT((fault_flags & VM_FAULT_WIRE_MASK) == 0);
 657
 658 RetryFault:
 659
 660         fs.first_object = object;
 661         first_pindex = OFF_TO_IDX(offset);
 662         fs.entry = &entry;
 663         fs.first_prot = fault_type;
 664         fs.wired = 0;
 665         /*fs.map_generation = 0; unused */
 666
 667         /*
 668          * Make a reference to this object to prevent its disposal while we
 669          * are messing with it.  Once we have the reference, the map is free
 670          * to be diddled.  Since objects reference their shadows (and copies),
 671          * they will stay around as well.
 672          *
 673          * Bump the paging-in-progress count to prevent size changes (e.g.
 674          * truncation operations) during I/O.  This must be done after
 675          * obtaining the vnode lock in order to avoid possible deadlocks.
 676          */
 677         vm_object_reference(fs.first_object);
 678         fs.vp = vnode_pager_lock(fs.first_object);
 679         vm_object_pip_add(fs.first_object, 1);
 680
 681         fs.lookup_still_valid = TRUE;
 682         fs.first_m = NULL;
 683         fs.object = fs.first_object;    /* so unlock_and_deallocate works */
 684
 685 #if 0
 686         /* XXX future - ability to operate on VM object using vpagetable */
 687         if (fs.entry->maptype == VM_MAPTYPE_VPAGETABLE) {
 688                 result = vm_fault_vpagetable(&fs, &first_pindex,
 689                                              fs.entry->aux.master_pde,
 690                                              fault_type);
 691                 if (result == KERN_TRY_AGAIN)
 692                         goto RetryFault;
 693                 if (result != KERN_SUCCESS) {
 694                         *errorp = result;
 695                         return (NULL);
 696                 }
 697         }
 698 #endif
 699
 700         /*
 701          * Now we have the actual (object, pindex), fault in the page.  If
 702          * vm_fault_object() fails it will unlock and deallocate the FS
 703          * data.   If it succeeds everything remains locked and fs->object
 704          * will have an additinal PIP count if it is not equal to
 705          * fs->first_object
 706          */
 707         result = vm_fault_object(&fs, first_pindex, fault_type);
 708
 709         if (result == KERN_TRY_AGAIN)
 710                 goto RetryFault;
 711         if (result != KERN_SUCCESS) {
 712                 *errorp = result;
 713                 return(NULL);
 714         }
 715
 716         if ((fault_type & VM_PROT_WRITE) && (fs.prot & VM_PROT_WRITE) == 0) {
 717                 *errorp = KERN_PROTECTION_FAILURE;
 718                 unlock_and_deallocate(&fs);
 719                 return(NULL);
 720         }
 721
 722         /*
 723          * On success vm_fault_object() does not unlock or deallocate, and fs.m
 724          * will contain a busied page.
 725          */
 726         unlock_things(&fs);
 727
 728         /*
 729          * Return a held page.  We are not doing any pmap manipulation so do
 730          * not set PG_MAPPED.  However, adjust the page flags according to
 731          * the fault type because the caller may not use a managed pmapping
 732          * (so we don't want to lose the fact that the page will be dirtied
 733          * if a write fault was specified).
 734          */
 735         vm_page_hold(fs.m);
 736         vm_page_flag_clear(fs.m, PG_ZERO);
 737         if (fault_type & VM_PROT_WRITE)
 738                 vm_page_dirty(fs.m);
 739
 740         /*
 741          * Indicate that the page was accessed.
 742          */
 743         vm_page_flag_set(fs.m, PG_REFERENCED);
 744
 745         /*
 746          * Unbusy the page by activating it.  It remains held and will not
 747          * be reclaimed.
 748          */
 749         vm_page_activate(fs.m);
 750
 751         if (curthread->td_lwp) {
 752                 if (fs.hardfault) {
 753                         mycpu->gd_cnt.v_vm_faults++;
 754                         curthread->td_lwp->lwp_ru.ru_majflt++;
 755                 } else {
 756                         curthread->td_lwp->lwp_ru.ru_minflt++;
 757                 }
 758         }
 759
 760         /*
 761          * Unlock everything, and return the held page.
 762          */
 763         vm_page_wakeup(fs.m);
 764         vm_object_deallocate(fs.first_object);
 765
 766         *errorp = 0;
 767         return(fs.m);
 768 }
 769
 770 /*
 771  * Translate the virtual page number (first_pindex) that is relative
 772  * to the address space into a logical page number that is relative to the
 773  * backing object.  Use the virtual page table pointed to by (vpte).
 774  *
 775  * This implements an N-level page table.  Any level can terminate the
 776  * scan by setting VPTE_PS.   A linear mapping is accomplished by setting
 777  * VPTE_PS in the master page directory entry set via mcontrol(MADV_SETMAP).
 778  */
 779 static
 780 int
 781 vm_fault_vpagetable(struct faultstate *fs, vm_pindex_t *pindex,
 782                     vpte_t vpte, int fault_type)
 783 {
 784         struct sf_buf *sf;
 785         int vshift = 32 - PAGE_SHIFT;   /* page index bits remaining */
 786         int result = KERN_SUCCESS;
 787         vpte_t *ptep;
 788
 789         for (;;) {
 790                 /*
 791                  * We cannot proceed if the vpte is not valid, not readable
 792                  * for a read fault, or not writable for a write fault.
 793                  */
 794                 if ((vpte & VPTE_V) == 0) {
 795                         unlock_and_deallocate(fs);
 796                         return (KERN_FAILURE);
 797                 }
 798                 if ((fault_type & VM_PROT_READ) && (vpte & VPTE_R) == 0) {
 799                         unlock_and_deallocate(fs);
 800                         return (KERN_FAILURE);
 801                 }
 802                 if ((fault_type & VM_PROT_WRITE) && (vpte & VPTE_W) == 0) {
 803                         unlock_and_deallocate(fs);
 804                         return (KERN_FAILURE);
 805                 }
 806                 if ((vpte & VPTE_PS) || vshift == 0)
 807                         break;
 808                 KKASSERT(vshift >= VPTE_PAGE_BITS);
 809
 810                 /*
 811                  * Get the page table page.  Nominally we only read the page
 812                  * table, but since we are actively setting VPTE_M and VPTE_A,
 813                  * tell vm_fault_object() that we are writing it.
 814                  *
 815                  * There is currently no real need to optimize this.
 816                  */
 817                 result = vm_fault_object(fs, vpte >> PAGE_SHIFT,
 818                                          VM_PROT_READ|VM_PROT_WRITE);
 819                 if (result != KERN_SUCCESS)
 820                         return (result);
 821
 822                 /*
 823                  * Process the returned fs.m and look up the page table
 824                  * entry in the page table page.
 825                  */
 826                 vshift -= VPTE_PAGE_BITS;
 827                 sf = sf_buf_alloc(fs->m, SFB_CPUPRIVATE);
 828                 ptep = ((vpte_t *)sf_buf_kva(sf) +
 829                         ((*pindex >> vshift) & VPTE_PAGE_MASK));
 830                 vpte = *ptep;
 831
 832                 /*
 833                  * Page table write-back.  If the vpte is valid for the
 834                  * requested operation, do a write-back to the page table.
 835                  *
 836                  * XXX VPTE_M is not set properly for page directory pages.
 837                  * It doesn't get set in the page directory if the page table
 838                  * is modified during a read access.
 839                  */
 840                 if ((fault_type & VM_PROT_WRITE) && (vpte & VPTE_V) &&
 841                     (vpte & VPTE_W)) {
 842                         if ((vpte & (VPTE_M|VPTE_A)) != (VPTE_M|VPTE_A)) {
 843                                 atomic_set_int(ptep, VPTE_M|VPTE_A);
 844                                 vm_page_dirty(fs->m);
 845                         }
 846                 }
 847                 if ((fault_type & VM_PROT_READ) && (vpte & VPTE_V) &&
 848                     (vpte & VPTE_R)) {
 849                         if ((vpte & VPTE_A) == 0) {
 850                                 atomic_set_int(ptep, VPTE_A);
 851                                 vm_page_dirty(fs->m);
 852                         }
 853                 }
 854                 sf_buf_free(sf);
 855                 vm_page_flag_set(fs->m, PG_REFERENCED);
 856                 vm_page_activate(fs->m);
 857                 vm_page_wakeup(fs->m);
 858                 cleanup_successful_fault(fs);
 859         }
 860         /*
 861          * Combine remaining address bits with the vpte.
 862          */
 863         *pindex = (vpte >> PAGE_SHIFT) +
 864                   (*pindex & ((1 << vshift) - 1));
 865         return (KERN_SUCCESS);
 866 }
 867
 868
 869 /*
 870  * Do all operations required to fault-in (fs.first_object, pindex).  Run
 871  * through the shadow chain as necessary and do required COW or virtual
 872  * copy operations.  The caller has already fully resolved the vm_map_entry
 873  * and, if appropriate, has created a copy-on-write layer.  All we need to
 874  * do is iterate the object chain.
 875  *
 876  * On failure (fs) is unlocked and deallocated and the caller may return or
 877  * retry depending on the failure code.  On success (fs) is NOT unlocked or
 878  * deallocated, fs.m will contained a resolved, busied page, and fs.object
 879  * will have an additional PIP count if it is not equal to fs.first_object.
 880  */
 881 static
 882 int
 883 vm_fault_object(struct faultstate *fs,
 884                 vm_pindex_t first_pindex, vm_prot_t fault_type)
 885 {
 886         vm_object_t next_object;
 887         vm_pindex_t pindex;
 888
 889         fs->prot = fs->first_prot;
 890         fs->object = fs->first_object;
 891         pindex = first_pindex;
 892
 893         /*
 894          * If a read fault occurs we try to make the page writable if
 895          * possible.  There are three cases where we cannot make the
 896          * page mapping writable:
 897          *
 898          * (1) The mapping is read-only or the VM object is read-only,
 899          *     fs->prot above will simply not have VM_PROT_WRITE set.
 900          *
 901          * (2) If the mapping is a virtual page table we need to be able
 902          *     to detect writes so we can set VPTE_M in the virtual page
 903          *     table.
 904          *
 905          * (3) If the VM page is read-only or copy-on-write, upgrading would
 906          *     just result in an unnecessary COW fault.
 907          *
 908          * VM_PROT_VPAGED is set if faulting via a virtual page table and
 909          * causes adjustments to the 'M'odify bit to also turn off write
 910          * access to force a re-fault.
 911          */
 912         if (fs->entry->maptype == VM_MAPTYPE_VPAGETABLE) {
 913                 if ((fault_type & VM_PROT_WRITE) == 0)
 914                         fs->prot &= ~VM_PROT_WRITE;
 915         }
 916
 917         for (;;) {
 918                 /*
 919                  * If the object is dead, we stop here
 920                  */
 921                 if (fs->object->flags & OBJ_DEAD) {
 922                         unlock_and_deallocate(fs);
 923                         return (KERN_PROTECTION_FAILURE);
 924                 }
 925
 926                 /*
 927                  * See if page is resident.  spl protection is required
 928                  * to avoid an interrupt unbusy/free race against our
 929                  * lookup.  We must hold the protection through a page
 930                  * allocation or busy.
 931                  */
 932                 crit_enter();
 933                 fs->m = vm_page_lookup(fs->object, pindex);
 934                 if (fs->m != NULL) {
 935                         int queue;
 936                         /*
 937                          * Wait/Retry if the page is busy.  We have to do this
 938                          * if the page is busy via either PG_BUSY or
 939                          * vm_page_t->busy because the vm_pager may be using
 940                          * vm_page_t->busy for pageouts ( and even pageins if
 941                          * it is the vnode pager ), and we could end up trying
 942                          * to pagein and pageout the same page simultaneously.
 943                          *
 944                          * We can theoretically allow the busy case on a read
 945                          * fault if the page is marked valid, but since such
 946                          * pages are typically already pmap'd, putting that
 947                          * special case in might be more effort then it is
 948                          * worth.  We cannot under any circumstances mess
 949                          * around with a vm_page_t->busy page except, perhaps,
 950                          * to pmap it.
 951                          */
 952                         if ((fs->m->flags & PG_BUSY) || fs->m->busy) {
 953                                 unlock_things(fs);
 954                                 vm_page_sleep_busy(fs->m, TRUE, "vmpfw");
 955                                 mycpu->gd_cnt.v_intrans++;
 956                                 vm_object_deallocate(fs->first_object);
 957                                 fs->first_object = NULL;
 958                                 crit_exit();
 959                                 return (KERN_TRY_AGAIN);
 960                         }
 961
 962                         /*
 963                          * If reactivating a page from PQ_CACHE we may have
 964                          * to rate-limit.
 965                          */
 966                         queue = fs->m->queue;
 967                         vm_page_unqueue_nowakeup(fs->m);
 968
 969                         if ((queue - fs->m->pc) == PQ_CACHE &&
 970                             vm_page_count_severe()) {
 971                                 vm_page_activate(fs->m);
 972                                 unlock_and_deallocate(fs);
 973                                 vm_waitpfault();
 974                                 crit_exit();
 975                                 return (KERN_TRY_AGAIN);
 976                         }
 977
 978                         /*
 979                          * Mark page busy for other processes, and the
 980                          * pagedaemon.  If it still isn't completely valid
 981                          * (readable), or if a read-ahead-mark is set on
 982                          * the VM page, jump to readrest, else we found the
 983                          * page and can return.
 984                          *
 985                          * We can release the spl once we have marked the
 986                          * page busy.
 987                          */
 988                         vm_page_busy(fs->m);
 989                         crit_exit();
 990
 991                         if (fs->m->object != &kernel_object) {
 992                                 if ((fs->m->valid & VM_PAGE_BITS_ALL) !=
 993                                     VM_PAGE_BITS_ALL) {
 994                                         goto readrest;
 995                                 }
 996                                 if (fs->m->flags & PG_RAM) {
 997                                         if (debug_cluster)
 998                                                 kprintf("R");
 999                                         vm_page_flag_clear(fs->m, PG_RAM);
1000                                         goto readrest;
1001                                 }
1002                         }
1003                         break; /* break to PAGE HAS BEEN FOUND */
1004                 }
1005
1006                 /*
1007                  * Page is not resident, If this is the search termination
1008                  * or the pager might contain the page, allocate a new page.
1009                  *
1010                  * NOTE: We are still in a critical section.
1011                  */
1012                 if (TRYPAGER(fs) || fs->object == fs->first_object) {
1013                         /*
1014                          * If the page is beyond the object size we fail
1015                          */
1016                         if (pindex >= fs->object->size) {
1017                                 crit_exit();
1018                                 unlock_and_deallocate(fs);
1019                                 return (KERN_PROTECTION_FAILURE);
1020                         }
1021
1022                         /*
1023                          * Ratelimit.
1024                          */
1025                         if (fs->didlimit == 0 && curproc != NULL) {
1026                                 int limticks;
1027
1028                                 limticks = vm_fault_ratelimit(curproc->p_vmspace);
1029                                 if (limticks) {
1030                                         crit_exit();
1031                                         unlock_and_deallocate(fs);
1032                                         tsleep(curproc, 0, "vmrate", limticks);
1033                                         fs->didlimit = 1;
1034                                         return (KERN_TRY_AGAIN);
1035                                 }
1036                         }
1037
1038                         /*
1039                          * Allocate a new page for this object/offset pair.
1040                          */
1041                         fs->m = NULL;
1042                         if (!vm_page_count_severe()) {
1043                                 fs->m = vm_page_alloc(fs->object, pindex,
1044                                     (fs->vp || fs->object->backing_object) ? VM_ALLOC_NORMAL : VM_ALLOC_NORMAL | VM_ALLOC_ZERO);
1045                         }
1046                         if (fs->m == NULL) {
1047                                 crit_exit();
1048                                 unlock_and_deallocate(fs);
1049                                 vm_waitpfault();
1050                                 return (KERN_TRY_AGAIN);
1051                         }
1052                 }
1053                 crit_exit();
1054
1055 readrest:
1056                 /*
1057                  * We have found an invalid or partially valid page, a
1058                  * potentially fully valid page with a read-ahead mark,
1059                  * or we have allocated a new page.
1060                  *
1061                  * Attempt to fault-in the page if there is a chance that the
1062                  * pager has it, and potentially fault in additional pages
1063                  * at the same time.
1064                  *
1065                  * We are NOT in splvm here and if TRYPAGER is true then
1066                  * fs.m will be non-NULL and will be PG_BUSY for us.
1067                  */
1068
1069                 if (TRYPAGER(fs)) {
1070                         int rv;
1071                         int seqaccess;
1072                         u_char behavior = vm_map_entry_behavior(fs->entry);
1073
1074                         if (behavior == MAP_ENTRY_BEHAV_RANDOM)
1075                                 seqaccess = 0;
1076                         else
1077                                 seqaccess = -1;
1078
1079                         /*
1080                          * If sequential access is detected then attempt
1081                          * to deactivate/cache pages behind the scan to
1082                          * prevent resource hogging.
1083                          *
1084                          * Use of PG_RAM to detect sequential access
1085                          * also simulates multi-zone sequential access
1086                          * detection for free.
1087                          *
1088                          * NOTE: Partially valid dirty pages cannot be
1089                          *       deactivated without causing NFS picemeal
1090                          *       writes to barf.
1091                          */
1092                         if ((fs->first_object->type != OBJT_DEVICE) &&
1093                             (behavior == MAP_ENTRY_BEHAV_SEQUENTIAL ||
1094                                 (behavior != MAP_ENTRY_BEHAV_RANDOM &&
1095                                  (fs->m->flags & PG_RAM)))
1096                         ) {
1097                                 vm_pindex_t scan_pindex;
1098                                 int scan_count = 16;
1099
1100                                 if (first_pindex < 16) {
1101                                         scan_pindex = 0;
1102                                         scan_count = 0;
1103                                 } else {
1104                                         scan_pindex = first_pindex - 16;
1105                                         if (scan_pindex < 16)
1106                                                 scan_count = scan_pindex;
1107                                         else
1108                                                 scan_count = 16;
1109                                 }
1110
1111                                 crit_enter();
1112                                 while (scan_count) {
1113                                         vm_page_t mt;
1114
1115                                         mt = vm_page_lookup(fs->first_object,
1116                                                             scan_pindex);
1117                                         if (mt == NULL ||
1118                                             (mt->valid != VM_PAGE_BITS_ALL)) {
1119                                                 break;
1120                                         }
1121                                         if (mt->busy ||
1122                                             (mt->flags & (PG_BUSY | PG_FICTITIOUS | PG_UNMANAGED)) ||
1123                                             mt->hold_count ||
1124                                             mt->wire_count)  {
1125                                                 goto skip;
1126                                         }
1127                                         if (mt->dirty == 0)
1128                                                 vm_page_test_dirty(mt);
1129                                         if (mt->dirty) {
1130                                                 vm_page_busy(mt);
1131                                                 vm_page_protect(mt,
1132                                                                 VM_PROT_NONE);
1133                                                 vm_page_deactivate(mt);
1134                                                 vm_page_wakeup(mt);
1135                                         } else {
1136                                                 vm_page_cache(mt);
1137                                         }
1138 skip:
1139                                         --scan_count;
1140                                         --scan_pindex;
1141                                 }
1142                                 crit_exit();
1143
1144                                 seqaccess = 1;
1145                         }
1146
1147                         /*
1148                          * Avoid deadlocking against the map when doing I/O.
1149                          * fs.object and the page is PG_BUSY'd.
1150                          */
1151                         unlock_map(fs);
1152
1153                         /*
1154                          * Acquire the page data.  We still hold a ref on
1155                          * fs.object and the page has been PG_BUSY's.
1156                          *
1157                          * The pager may replace the page (for example, in
1158                          * order to enter a fictitious page into the
1159                          * object).  If it does so it is responsible for
1160                          * cleaning up the passed page and properly setting
1161                          * the new page PG_BUSY.
1162                          */
1163                         if (vm_pager_has_page(fs->object, pindex)) {
1164                                 rv = vm_pager_get_page(fs->object, &fs->m,
1165                                                        seqaccess);
1166                         } else {
1167                                 rv = VM_PAGER_FAIL;
1168                         }
1169
1170                         if (rv == VM_PAGER_OK) {
1171                                 /*
1172                                  * Relookup in case pager changed page. Pager
1173                                  * is responsible for disposition of old page
1174                                  * if moved.
1175                                  *
1176                                  * XXX other code segments do relookups too.
1177                                  * It's a bad abstraction that needs to be
1178                                  * fixed/removed.
1179                                  */
1180                                 fs->m = vm_page_lookup(fs->object, pindex);
1181                                 if (fs->m == NULL) {
1182                                         unlock_and_deallocate(fs);
1183                                         return (KERN_TRY_AGAIN);
1184                                 }
1185
1186                                 ++fs->hardfault;
1187                                 break; /* break to PAGE HAS BEEN FOUND */
1188                         }
1189
1190                         /*
1191                          * Remove the bogus page (which does not exist at this
1192                          * object/offset); before doing so, we must get back
1193                          * our object lock to preserve our invariant.
1194                          *
1195                          * Also wake up any other process that may want to bring
1196                          * in this page.
1197                          *
1198                          * If this is the top-level object, we must leave the
1199                          * busy page to prevent another process from rushing
1200                          * past us, and inserting the page in that object at
1201                          * the same time that we are.
1202                          */
1203                         if (rv == VM_PAGER_ERROR) {
1204                                 if (curproc)
1205                                         kprintf("vm_fault: pager read error, pid %d (%s)\n", curproc->p_pid, curproc->p_comm);
1206                                 else
1207                                         kprintf("vm_fault: pager read error, thread %p (%s)\n", curthread, curproc->p_comm);
1208                         }
1209
1210                         /*
1211                          * Data outside the range of the pager or an I/O error
1212                          *
1213                          * The page may have been wired during the pagein,
1214                          * e.g. by the buffer cache, and cannot simply be
1215                          * freed.  Call vnode_pager_freepage() to deal with it.
1216                          */
1217                         /*
1218                          * XXX - the check for kernel_map is a kludge to work
1219                          * around having the machine panic on a kernel space
1220                          * fault w/ I/O error.
1221                          */
1222                         if (((fs->map != &kernel_map) &&
1223                             (rv == VM_PAGER_ERROR)) || (rv == VM_PAGER_BAD)) {
1224                                 vnode_pager_freepage(fs->m);
1225                                 fs->m = NULL;
1226                                 unlock_and_deallocate(fs);
1227                                 if (rv == VM_PAGER_ERROR)
1228                                         return (KERN_FAILURE);
1229                                 else
1230                                         return (KERN_PROTECTION_FAILURE);
1231                                 /* NOT REACHED */
1232                         }
1233                         if (fs->object != fs->first_object) {
1234                                 vnode_pager_freepage(fs->m);
1235                                 fs->m = NULL;
1236                                 /*
1237                                  * XXX - we cannot just fall out at this
1238                                  * point, m has been freed and is invalid!
1239                                  */
1240                         }
1241                 }
1242
1243                 /*
1244                  * We get here if the object has a default pager (or unwiring)
1245                  * or the pager doesn't have the page.
1246                  */
1247                 if (fs->object == fs->first_object)
1248                         fs->first_m = fs->m;
1249
1250                 /*
1251                  * Move on to the next object.  Lock the next object before
1252                  * unlocking the current one.
1253                  */
1254                 pindex += OFF_TO_IDX(fs->object->backing_object_offset);
1255                 next_object = fs->object->backing_object;
1256                 if (next_object == NULL) {
1257                         /*
1258                          * If there's no object left, fill the page in the top
1259                          * object with zeros.
1260                          */
1261                         if (fs->object != fs->first_object) {
1262                                 vm_object_pip_wakeup(fs->object);
1263
1264                                 fs->object = fs->first_object;
1265                                 pindex = first_pindex;
1266                                 fs->m = fs->first_m;
1267                         }
1268                         fs->first_m = NULL;
1269
1270                         /*
1271                          * Zero the page if necessary and mark it valid.
1272                          */
1273                         if ((fs->m->flags & PG_ZERO) == 0) {
1274                                 vm_page_zero_fill(fs->m);
1275                         } else {
1276                                 mycpu->gd_cnt.v_ozfod++;
1277                         }
1278                         mycpu->gd_cnt.v_zfod++;
1279                         fs->m->valid = VM_PAGE_BITS_ALL;
1280                         break;  /* break to PAGE HAS BEEN FOUND */
1281                 } else {
1282                         if (fs->object != fs->first_object) {
1283                                 vm_object_pip_wakeup(fs->object);
1284                         }
1285                         KASSERT(fs->object != next_object, ("object loop %p", next_object));
1286                         fs->object = next_object;
1287                         vm_object_pip_add(fs->object, 1);
1288                 }
1289         }
1290
1291         /*
1292          * PAGE HAS BEEN FOUND. [Loop invariant still holds -- the object lock
1293          * is held.]
1294          *
1295          * If the page is being written, but isn't already owned by the
1296          * top-level object, we have to copy it into a new page owned by the
1297          * top-level object.
1298          */
1299         KASSERT((fs->m->flags & PG_BUSY) != 0,
1300                 ("vm_fault: not busy after main loop"));
1301
1302         if (fs->object != fs->first_object) {
1303                 /*
1304                  * We only really need to copy if we want to write it.
1305                  */
1306                 if (fault_type & VM_PROT_WRITE) {
1307                         /*
1308                          * This allows pages to be virtually copied from a
1309                          * backing_object into the first_object, where the
1310                          * backing object has no other refs to it, and cannot
1311                          * gain any more refs.  Instead of a bcopy, we just
1312                          * move the page from the backing object to the
1313                          * first object.  Note that we must mark the page
1314                          * dirty in the first object so that it will go out
1315                          * to swap when needed.
1316                          */
1317                         if (
1318                                 /*
1319                                  * Map, if present, has not changed
1320                                  */
1321                                 (fs->map == NULL ||
1322                                 fs->map_generation == fs->map->timestamp) &&
1323                                 /*
1324                                  * Only one shadow object
1325                                  */
1326                                 (fs->object->shadow_count == 1) &&
1327                                 /*
1328                                  * No COW refs, except us
1329                                  */
1330                                 (fs->object->ref_count == 1) &&
1331                                 /*
1332                                  * No one else can look this object up
1333                                  */
1334                                 (fs->object->handle == NULL) &&
1335                                 /*
1336                                  * No other ways to look the object up
1337                                  */
1338                                 ((fs->object->type == OBJT_DEFAULT) ||
1339                                  (fs->object->type == OBJT_SWAP)) &&
1340                                 /*
1341                                  * We don't chase down the shadow chain
1342                                  */
1343                                 (fs->object == fs->first_object->backing_object) &&
1344
1345                                 /*
1346                                  * grab the lock if we need to
1347                                  */
1348                                 (fs->lookup_still_valid ||
1349                                  fs->map == NULL ||
1350                                  lockmgr(&fs->map->lock, LK_EXCLUSIVE|LK_NOWAIT) == 0)
1351                             ) {
1352
1353                                 fs->lookup_still_valid = 1;
1354                                 /*
1355                                  * get rid of the unnecessary page
1356                                  */
1357                                 vm_page_protect(fs->first_m, VM_PROT_NONE);
1358                                 vm_page_free(fs->first_m);
1359                                 fs->first_m = NULL;
1360
1361                                 /*
1362                                  * grab the page and put it into the
1363                                  * process'es object.  The page is
1364                                  * automatically made dirty.
1365                                  */
1366                                 vm_page_rename(fs->m, fs->first_object, first_pindex);
1367                                 fs->first_m = fs->m;
1368                                 vm_page_busy(fs->first_m);
1369                                 fs->m = NULL;
1370                                 mycpu->gd_cnt.v_cow_optim++;
1371                         } else {
1372                                 /*
1373                                  * Oh, well, lets copy it.
1374                                  */
1375                                 vm_page_copy(fs->m, fs->first_m);
1376                                 vm_page_event(fs->m, VMEVENT_COW);
1377                         }
1378
1379                         if (fs->m) {
1380                                 /*
1381                                  * We no longer need the old page or object.
1382                                  */
1383                                 release_page(fs);
1384                         }
1385
1386                         /*
1387                          * fs->object != fs->first_object due to above
1388                          * conditional
1389                          */
1390                         vm_object_pip_wakeup(fs->object);
1391
1392                         /*
1393                          * Only use the new page below...
1394                          */
1395
1396                         mycpu->gd_cnt.v_cow_faults++;
1397                         fs->m = fs->first_m;
1398                         fs->object = fs->first_object;
1399                         pindex = first_pindex;
1400                 } else {
1401                         /*
1402                          * If it wasn't a write fault avoid having to copy
1403                          * the page by mapping it read-only.
1404                          */
1405                         fs->prot &= ~VM_PROT_WRITE;
1406                 }
1407         }
1408
1409         /*
1410          * We may have had to unlock a map to do I/O.  If we did then
1411          * lookup_still_valid will be FALSE.  If the map generation count
1412          * also changed then all sorts of things could have happened while
1413          * we were doing the I/O and we need to retry.
1414          */
1415
1416         if (!fs->lookup_still_valid &&
1417             fs->map != NULL &&
1418             (fs->map->timestamp != fs->map_generation)) {
1419                 release_page(fs);
1420                 unlock_and_deallocate(fs);
1421                 return (KERN_TRY_AGAIN);
1422         }
1423
1424         /*
1425          * If the fault is a write, we know that this page is being
1426          * written NOW so dirty it explicitly to save on pmap_is_modified()
1427          * calls later.
1428          *
1429          * If this is a NOSYNC mmap we do not want to set PG_NOSYNC
1430          * if the page is already dirty to prevent data written with
1431          * the expectation of being synced from not being synced.
1432          * Likewise if this entry does not request NOSYNC then make
1433          * sure the page isn't marked NOSYNC.  Applications sharing
1434          * data should use the same flags to avoid ping ponging.
1435          *
1436          * Also tell the backing pager, if any, that it should remove
1437          * any swap backing since the page is now dirty.
1438          */
1439         if (fs->prot & VM_PROT_WRITE) {
1440                 vm_object_set_writeable_dirty(fs->m->object);
1441                 if (fs->entry->eflags & MAP_ENTRY_NOSYNC) {
1442                         if (fs->m->dirty == 0)
1443                                 vm_page_flag_set(fs->m, PG_NOSYNC);
1444                 } else {
1445                         vm_page_flag_clear(fs->m, PG_NOSYNC);
1446                 }
1447                 if (fs->fault_flags & VM_FAULT_DIRTY) {
1448                         crit_enter();
1449                         vm_page_dirty(fs->m);
1450                         vm_pager_page_unswapped(fs->m);
1451                         crit_exit();
1452                 }
1453         }
1454
1455         /*
1456          * Page had better still be busy.  We are still locked up and
1457          * fs->object will have another PIP reference if it is not equal
1458          * to fs->first_object.
1459          */
1460         KASSERT(fs->m->flags & PG_BUSY,
1461                 ("vm_fault: page %p not busy!", fs->m));
1462
1463         /*
1464          * Sanity check: page must be completely valid or it is not fit to
1465          * map into user space.  vm_pager_get_pages() ensures this.
1466          */
1467         if (fs->m->valid != VM_PAGE_BITS_ALL) {
1468                 vm_page_zero_invalid(fs->m, TRUE);
1469                 kprintf("Warning: page %p partially invalid on fault\n", fs->m);
1470         }
1471
1472         return (KERN_SUCCESS);
1473 }
1474
1475 /*
1476  * Wire down a range of virtual addresses in a map.  The entry in question
1477  * should be marked in-transition and the map must be locked.  We must
1478  * release the map temporarily while faulting-in the page to avoid a
1479  * deadlock.  Note that the entry may be clipped while we are blocked but
1480  * will never be freed.
1481  */
1482 int
1483 vm_fault_wire(vm_map_t map, vm_map_entry_t entry, boolean_t user_wire)
1484 {
1485         boolean_t fictitious;
1486         vm_offset_t start;
1487         vm_offset_t end;
1488         vm_offset_t va;
1489         vm_paddr_t pa;
1490         pmap_t pmap;
1491         int rv;
1492
1493         pmap = vm_map_pmap(map);
1494         start = entry->start;
1495         end = entry->end;
1496         fictitious = entry->object.vm_object &&
1497                         (entry->object.vm_object->type == OBJT_DEVICE);
1498
1499         vm_map_unlock(map);
1500         map->timestamp++;
1501
1502         /*
1503          * We simulate a fault to get the page and enter it in the physical
1504          * map.
1505          */
1506         for (va = start; va < end; va += PAGE_SIZE) {
1507                 if (user_wire) {
1508                         rv = vm_fault(map, va, VM_PROT_READ,
1509                                         VM_FAULT_USER_WIRE);
1510                 } else {
1511                         rv = vm_fault(map, va, VM_PROT_READ|VM_PROT_WRITE,
1512                                         VM_FAULT_CHANGE_WIRING);
1513                 }
1514                 if (rv) {
1515                         while (va > start) {
1516                                 va -= PAGE_SIZE;
1517                                 if ((pa = pmap_extract(pmap, va)) == 0)
1518                                         continue;
1519                                 pmap_change_wiring(pmap, va, FALSE);
1520                                 if (!fictitious)
1521                                         vm_page_unwire(PHYS_TO_VM_PAGE(pa), 1);
1522                         }
1523                         vm_map_lock(map);
1524                         return (rv);
1525                 }
1526         }
1527         vm_map_lock(map);
1528         return (KERN_SUCCESS);
1529 }
1530
1531 /*
1532  * Unwire a range of virtual addresses in a map.  The map should be
1533  * locked.
1534  */
1535 void
1536 vm_fault_unwire(vm_map_t map, vm_map_entry_t entry)
1537 {
1538         boolean_t fictitious;
1539         vm_offset_t start;
1540         vm_offset_t end;
1541         vm_offset_t va;
1542         vm_paddr_t pa;
1543         pmap_t pmap;
1544
1545         pmap = vm_map_pmap(map);
1546         start = entry->start;
1547         end = entry->end;
1548         fictitious = entry->object.vm_object &&
1549                         (entry->object.vm_object->type == OBJT_DEVICE);
1550
1551         /*
1552          * Since the pages are wired down, we must be able to get their
1553          * mappings from the physical map system.
1554          */
1555         for (va = start; va < end; va += PAGE_SIZE) {
1556                 pa = pmap_extract(pmap, va);
1557                 if (pa != 0) {
1558                         pmap_change_wiring(pmap, va, FALSE);
1559                         if (!fictitious)
1560                                 vm_page_unwire(PHYS_TO_VM_PAGE(pa), 1);
1561                 }
1562         }
1563 }
1564
1565 /*
1566  * Reduce the rate at which memory is allocated to a process based
1567  * on the perceived load on the VM system. As the load increases
1568  * the allocation burst rate goes down and the delay increases.
1569  *
1570  * Rate limiting does not apply when faulting active or inactive
1571  * pages.  When faulting 'cache' pages, rate limiting only applies
1572  * if the system currently has a severe page deficit.
1573  *
1574  * XXX vm_pagesupply should be increased when a page is freed.
1575  *
1576  * We sleep up to 1/10 of a second.
1577  */
1578 static int
1579 vm_fault_ratelimit(struct vmspace *vmspace)
1580 {
1581         if (vm_load_enable == 0)
1582                 return(0);
1583         if (vmspace->vm_pagesupply > 0) {
1584                 --vmspace->vm_pagesupply;
1585                 return(0);
1586         }
1587 #ifdef INVARIANTS
1588         if (vm_load_debug) {
1589                 kprintf("load %-4d give %d pgs, wait %d, pid %-5d (%s)\n",
1590                         vm_load,
1591                         (1000 - vm_load ) / 10, vm_load * hz / 10000,
1592                         curproc->p_pid, curproc->p_comm);
1593         }
1594 #endif
1595         vmspace->vm_pagesupply = (1000 - vm_load) / 10;
1596         return(vm_load * hz / 10000);
1597 }
1598
1599 /*
1600  *      Routine:
1601  *              vm_fault_copy_entry
1602  *      Function:
1603  *              Copy all of the pages from a wired-down map entry to another.
1604  *
1605  *      In/out conditions:
1606  *              The source and destination maps must be locked for write.
1607  *              The source map entry must be wired down (or be a sharing map
1608  *              entry corresponding to a main map entry that is wired down).
1609  */
1610
1611 void
1612 vm_fault_copy_entry(vm_map_t dst_map, vm_map_t src_map,
1613     vm_map_entry_t dst_entry, vm_map_entry_t src_entry)
1614 {
1615         vm_object_t dst_object;
1616         vm_object_t src_object;
1617         vm_ooffset_t dst_offset;
1618         vm_ooffset_t src_offset;
1619         vm_prot_t prot;
1620         vm_offset_t vaddr;
1621         vm_page_t dst_m;
1622         vm_page_t src_m;
1623
1624 #ifdef  lint
1625         src_map++;
1626 #endif  /* lint */
1627
1628         src_object = src_entry->object.vm_object;
1629         src_offset = src_entry->offset;
1630
1631         /*
1632          * Create the top-level object for the destination entry. (Doesn't
1633          * actually shadow anything - we copy the pages directly.)
1634          */
1635         vm_map_entry_allocate_object(dst_entry);
1636         dst_object = dst_entry->object.vm_object;
1637
1638         prot = dst_entry->max_protection;
1639
1640         /*
1641          * Loop through all of the pages in the entry's range, copying each
1642          * one from the source object (it should be there) to the destination
1643          * object.
1644          */
1645         for (vaddr = dst_entry->start, dst_offset = 0;
1646             vaddr < dst_entry->end;
1647             vaddr += PAGE_SIZE, dst_offset += PAGE_SIZE) {
1648
1649                 /*
1650                  * Allocate a page in the destination object
1651                  */
1652                 do {
1653                         dst_m = vm_page_alloc(dst_object,
1654                                 OFF_TO_IDX(dst_offset), VM_ALLOC_NORMAL);
1655                         if (dst_m == NULL) {
1656                                 vm_wait(0);
1657                         }
1658                 } while (dst_m == NULL);
1659
1660                 /*
1661                  * Find the page in the source object, and copy it in.
1662                  * (Because the source is wired down, the page will be in
1663                  * memory.)
1664                  */
1665                 src_m = vm_page_lookup(src_object,
1666                         OFF_TO_IDX(dst_offset + src_offset));
1667                 if (src_m == NULL)
1668                         panic("vm_fault_copy_wired: page missing");
1669
1670                 vm_page_copy(src_m, dst_m);
1671                 vm_page_event(src_m, VMEVENT_COW);
1672
1673                 /*
1674                  * Enter it in the pmap...
1675                  */
1676
1677                 vm_page_flag_clear(dst_m, PG_ZERO);
1678                 pmap_enter(dst_map->pmap, vaddr, dst_m, prot, FALSE);
1679
1680                 /*
1681                  * Mark it no longer busy, and put it on the active list.
1682                  */
1683                 vm_page_activate(dst_m);
1684                 vm_page_wakeup(dst_m);
1685         }
1686 }
1687
1688 #if 0
1689
1690 /*
1691  * This routine checks around the requested page for other pages that
1692  * might be able to be faulted in.  This routine brackets the viable
1693  * pages for the pages to be paged in.
1694  *
1695  * Inputs:
1696  *      m, rbehind, rahead
1697  *
1698  * Outputs:
1699  *  marray (array of vm_page_t), reqpage (index of requested page)
1700  *
1701  * Return value:
1702  *  number of pages in marray
1703  */
1704 static int
1705 vm_fault_additional_pages(vm_page_t m, int rbehind, int rahead,
1706                           vm_page_t *marray, int *reqpage)
1707 {
1708         int i,j;
1709         vm_object_t object;
1710         vm_pindex_t pindex, startpindex, endpindex, tpindex;
1711         vm_page_t rtm;
1712         int cbehind, cahead;
1713
1714         object = m->object;
1715         pindex = m->pindex;
1716
1717         /*
1718          * we don't fault-ahead for device pager
1719          */
1720         if (object->type == OBJT_DEVICE) {
1721                 *reqpage = 0;
1722                 marray[0] = m;
1723                 return 1;
1724         }
1725
1726         /*
1727          * if the requested page is not available, then give up now
1728          */
1729         if (!vm_pager_has_page(object, pindex, &cbehind, &cahead)) {
1730                 *reqpage = 0;   /* not used by caller, fix compiler warn */
1731                 return 0;
1732         }
1733
1734         if ((cbehind == 0) && (cahead == 0)) {
1735                 *reqpage = 0;
1736                 marray[0] = m;
1737                 return 1;
1738         }
1739
1740         if (rahead > cahead) {
1741                 rahead = cahead;
1742         }
1743
1744         if (rbehind > cbehind) {
1745                 rbehind = cbehind;
1746         }
1747
1748         /*
1749          * Do not do any readahead if we have insufficient free memory.
1750          *
1751          * XXX code was broken disabled before and has instability
1752          * with this conditonal fixed, so shortcut for now.
1753          */
1754         if (burst_fault == 0 || vm_page_count_severe()) {
1755                 marray[0] = m;
1756                 *reqpage = 0;
1757                 return 1;
1758         }
1759
1760         /*
1761          * scan backward for the read behind pages -- in memory
1762          *
1763          * Assume that if the page is not found an interrupt will not
1764          * create it.  Theoretically interrupts can only remove (busy)
1765          * pages, not create new associations.
1766          */
1767         if (pindex > 0) {
1768                 if (rbehind > pindex) {
1769                         rbehind = pindex;
1770                         startpindex = 0;
1771                 } else {
1772                         startpindex = pindex - rbehind;
1773                 }
1774
1775                 crit_enter();
1776                 for (tpindex = pindex; tpindex > startpindex; --tpindex) {
1777                         if (vm_page_lookup(object, tpindex - 1))
1778                                 break;
1779                 }
1780
1781                 i = 0;
1782                 while (tpindex < pindex) {
1783                         rtm = vm_page_alloc(object, tpindex, VM_ALLOC_SYSTEM);
1784                         if (rtm == NULL) {
1785                                 crit_exit();
1786                                 for (j = 0; j < i; j++) {
1787                                         vm_page_free(marray[j]);
1788                                 }
1789                                 marray[0] = m;
1790                                 *reqpage = 0;
1791                                 return 1;
1792                         }
1793                         marray[i] = rtm;
1794                         ++i;
1795                         ++tpindex;
1796                 }
1797                 crit_exit();
1798         } else {
1799                 i = 0;
1800         }
1801
1802         /*
1803          * Assign requested page
1804          */
1805         marray[i] = m;
1806         *reqpage = i;
1807         ++i;
1808
1809         /*
1810          * Scan forwards for read-ahead pages
1811          */
1812         tpindex = pindex + 1;
1813         endpindex = tpindex + rahead;
1814         if (endpindex > object->size)
1815                 endpindex = object->size;
1816
1817         crit_enter();
1818         while (tpindex < endpindex) {
1819                 if (vm_page_lookup(object, tpindex))
1820                         break;
1821                 rtm = vm_page_alloc(object, tpindex, VM_ALLOC_SYSTEM);
1822                 if (rtm == NULL)
1823                         break;
1824                 marray[i] = rtm;
1825                 ++i;
1826                 ++tpindex;
1827         }
1828         crit_exit();
1829
1830         return (i);
1831 }
1832
1833 #endif
1834
1835 /*
1836  * vm_prefault() provides a quick way of clustering pagefaults into a
1837  * processes address space.  It is a "cousin" of pmap_object_init_pt,
1838  * except it runs at page fault time instead of mmap time.
1839  *
1840  * This code used to be per-platform pmap_prefault().  It is now
1841  * machine-independent and enhanced to also pre-fault zero-fill pages
1842  * (see vm.fast_fault) as well as make them writable, which greatly
1843  * reduces the number of page faults programs incur.
1844  *
1845  * Application performance when pre-faulting zero-fill pages is heavily
1846  * dependent on the application.  Very tiny applications like /bin/echo
1847  * lose a little performance while applications of any appreciable size
1848  * gain performance.  Prefaulting multiple pages also reduces SMP
1849  * congestion and can improve SMP performance significantly.
1850  *
1851  * NOTE!  prot may allow writing but this only applies to the top level
1852  *        object.  If we wind up mapping a page extracted from a backing
1853  *        object we have to make sure it is read-only.
1854  *
1855  * NOTE!  The caller has already handled any COW operations on the
1856  *        vm_map_entry via the normal fault code.  Do NOT call this
1857  *        shortcut unless the normal fault code has run on this entry.
1858  */
1859 #define PFBAK 4
1860 #define PFFOR 4
1861 #define PAGEORDER_SIZE (PFBAK+PFFOR)
1862
1863 static int vm_prefault_pageorder[] = {
1864         -PAGE_SIZE, PAGE_SIZE,
1865         -2 * PAGE_SIZE, 2 * PAGE_SIZE,
1866         -3 * PAGE_SIZE, 3 * PAGE_SIZE,
1867         -4 * PAGE_SIZE, 4 * PAGE_SIZE
1868 };
1869
1870 static void
1871 vm_prefault(pmap_t pmap, vm_offset_t addra, vm_map_entry_t entry, int prot)
1872 {
1873         struct lwp *lp;
1874         vm_page_t m;
1875         vm_offset_t starta;
1876         vm_offset_t addr;
1877         vm_pindex_t index;
1878         vm_pindex_t pindex;
1879         vm_object_t object;
1880         int pprot;
1881         int i;
1882
1883         /*
1884          * We do not currently prefault mappings that use virtual page
1885          * tables.  We do not prefault foreign pmaps.
1886          */
1887         if (entry->maptype == VM_MAPTYPE_VPAGETABLE)
1888                 return;
1889         lp = curthread->td_lwp;
1890         if (lp == NULL || (pmap != vmspace_pmap(lp->lwp_vmspace)))
1891                 return;
1892
1893         object = entry->object.vm_object;
1894
1895         starta = addra - PFBAK * PAGE_SIZE;
1896         if (starta < entry->start)
1897                 starta = entry->start;
1898         else if (starta > addra)
1899                 starta = 0;
1900
1901         /*
1902          * critical section protection is required to maintain the
1903          * page/object association, interrupts can free pages and remove
1904          * them from their objects.
1905          */
1906         crit_enter();
1907         for (i = 0; i < PAGEORDER_SIZE; i++) {
1908                 vm_object_t lobject;
1909
1910                 addr = addra + vm_prefault_pageorder[i];
1911                 if (addr > addra + (PFFOR * PAGE_SIZE))
1912                         addr = 0;
1913
1914                 if (addr < starta || addr >= entry->end)
1915                         continue;
1916
1917                 if (pmap_prefault_ok(pmap, addr) == 0)
1918                         continue;
1919
1920                 /*
1921                  * Follow the VM object chain to obtain the page to be mapped
1922                  * into the pmap.
1923                  *
1924                  * If we reach the terminal object without finding a page
1925                  * and we determine it would be advantageous, then allocate
1926                  * a zero-fill page for the base object.  The base object
1927                  * is guaranteed to be OBJT_DEFAULT for this case.
1928                  */
1929                 index = ((addr - entry->start) + entry->offset) >> PAGE_SHIFT;
1930                 lobject = object;
1931                 pindex = index;
1932                 pprot = prot;
1933
1934                 while ((m = vm_page_lookup(lobject, pindex)) == NULL) {
1935                         if (lobject->type != OBJT_DEFAULT)
1936                                 break;
1937                         if (lobject->backing_object == NULL) {
1938                                 if (vm_fast_fault == 0)
1939                                         break;
1940                                 if (vm_prefault_pageorder[i] < 0 ||
1941                                     (prot & VM_PROT_WRITE) == 0 ||
1942                                     vm_page_count_min(0)) {
1943                                         break;
1944                                 }
1945                                 m = vm_page_alloc(object, index,
1946                                               VM_ALLOC_NORMAL | VM_ALLOC_ZERO);
1947
1948                                 if ((m->flags & PG_ZERO) == 0) {
1949                                         vm_page_zero_fill(m);
1950                                 } else {
1951                                         vm_page_flag_clear(m, PG_ZERO);
1952                                         mycpu->gd_cnt.v_ozfod++;
1953                                 }
1954                                 mycpu->gd_cnt.v_zfod++;
1955                                 m->valid = VM_PAGE_BITS_ALL;
1956                                 vm_page_wakeup(m);
1957                                 pprot = prot;
1958                                 /* lobject = object .. not needed */
1959                                 break;
1960                         }
1961                         if (lobject->backing_object_offset & PAGE_MASK)
1962                                 break;
1963                         pindex += lobject->backing_object_offset >> PAGE_SHIFT;
1964                         lobject = lobject->backing_object;
1965                         pprot &= ~VM_PROT_WRITE;
1966                 }
1967                 /*
1968                  * NOTE: lobject now invalid (if we did a zero-fill we didn't
1969                  *       bother assigning lobject = object).
1970                  *
1971                  * Give-up if the page is not available.
1972                  */
1973                 if (m == NULL)
1974                         break;
1975
1976                 /*
1977                  * Do not conditionalize on PG_RAM.  If pages are present in
1978                  * the VM system we assume optimal caching.  If caching is
1979                  * not optimal the I/O gravy train will be restarted when we
1980                  * hit an unavailable page.  We do not want to try to restart
1981                  * the gravy train now because we really don't know how much
1982                  * of the object has been cached.  The cost for restarting
1983                  * the gravy train should be low (since accesses will likely
1984                  * be I/O bound anyway).
1985                  *
1986                  * The object must be marked dirty if we are mapping a
1987                  * writable page.
1988                  */
1989                 if (pprot & VM_PROT_WRITE)
1990                         vm_object_set_writeable_dirty(m->object);
1991
1992                 /*
1993                  * Enter the page into the pmap if appropriate.
1994                  */
1995                 if (((m->valid & VM_PAGE_BITS_ALL) == VM_PAGE_BITS_ALL) &&
1996                     (m->busy == 0) &&
1997                     (m->flags & (PG_BUSY | PG_FICTITIOUS)) == 0) {
1998
1999                         if ((m->queue - m->pc) == PQ_CACHE) {
2000                                 vm_page_deactivate(m);
2001                         }
2002                         vm_page_busy(m);
2003                         pmap_enter(pmap, addr, m, pprot, 0);
2004                         vm_page_wakeup(m);
2005                 }
2006         }
2007         crit_exit();
2008 }