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                  * page with a read-ahead mark which might be partially or
1059                  * fully valid (and maybe dirty too), or we have allocated
1060                  * a new page.
1061                  *
1062                  * Attempt to fault-in the page if there is a chance that the
1063                  * pager has it, and potentially fault in additional pages
1064                  * at the same time.
1065                  *
1066                  * We are NOT in splvm here and if TRYPAGER is true then
1067                  * fs.m will be non-NULL and will be PG_BUSY for us.
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 we got here through a PG_RAM read-ahead
1164                          * mark the page may be partially dirty and thus
1165                          * not freeable.  Don't bother checking to see
1166                          * if the pager has the page because we can't free
1167                          * it anyway.  We have to depend on the get_page
1168                          * operation filling in any gaps whether there is
1169                          * backing store or not.
1170                          */
1171                         rv = vm_pager_get_page(fs->object, &fs->m, seqaccess);
1172
1173                         if (rv == VM_PAGER_OK) {
1174                                 /*
1175                                  * Relookup in case pager changed page. Pager
1176                                  * is responsible for disposition of old page
1177                                  * if moved.
1178                                  *
1179                                  * XXX other code segments do relookups too.
1180                                  * It's a bad abstraction that needs to be
1181                                  * fixed/removed.
1182                                  */
1183                                 fs->m = vm_page_lookup(fs->object, pindex);
1184                                 if (fs->m == NULL) {
1185                                         unlock_and_deallocate(fs);
1186                                         return (KERN_TRY_AGAIN);
1187                                 }
1188
1189                                 ++fs->hardfault;
1190                                 break; /* break to PAGE HAS BEEN FOUND */
1191                         }
1192
1193                         /*
1194                          * Remove the bogus page (which does not exist at this
1195                          * object/offset); before doing so, we must get back
1196                          * our object lock to preserve our invariant.
1197                          *
1198                          * Also wake up any other process that may want to bring
1199                          * in this page.
1200                          *
1201                          * If this is the top-level object, we must leave the
1202                          * busy page to prevent another process from rushing
1203                          * past us, and inserting the page in that object at
1204                          * the same time that we are.
1205                          */
1206                         if (rv == VM_PAGER_ERROR) {
1207                                 if (curproc)
1208                                         kprintf("vm_fault: pager read error, pid %d (%s)\n", curproc->p_pid, curproc->p_comm);
1209                                 else
1210                                         kprintf("vm_fault: pager read error, thread %p (%s)\n", curthread, curproc->p_comm);
1211                         }
1212
1213                         /*
1214                          * Data outside the range of the pager or an I/O error
1215                          *
1216                          * The page may have been wired during the pagein,
1217                          * e.g. by the buffer cache, and cannot simply be
1218                          * freed.  Call vnode_pager_freepage() to deal with it.
1219                          */
1220                         /*
1221                          * XXX - the check for kernel_map is a kludge to work
1222                          * around having the machine panic on a kernel space
1223                          * fault w/ I/O error.
1224                          */
1225                         if (((fs->map != &kernel_map) &&
1226                             (rv == VM_PAGER_ERROR)) || (rv == VM_PAGER_BAD)) {
1227                                 vnode_pager_freepage(fs->m);
1228                                 fs->m = NULL;
1229                                 unlock_and_deallocate(fs);
1230                                 if (rv == VM_PAGER_ERROR)
1231                                         return (KERN_FAILURE);
1232                                 else
1233                                         return (KERN_PROTECTION_FAILURE);
1234                                 /* NOT REACHED */
1235                         }
1236                         if (fs->object != fs->first_object) {
1237                                 vnode_pager_freepage(fs->m);
1238                                 fs->m = NULL;
1239                                 /*
1240                                  * XXX - we cannot just fall out at this
1241                                  * point, m has been freed and is invalid!
1242                                  */
1243                         }
1244                 }
1245
1246                 /*
1247                  * We get here if the object has a default pager (or unwiring)
1248                  * or the pager doesn't have the page.
1249                  */
1250                 if (fs->object == fs->first_object)
1251                         fs->first_m = fs->m;
1252
1253                 /*
1254                  * Move on to the next object.  Lock the next object before
1255                  * unlocking the current one.
1256                  */
1257                 pindex += OFF_TO_IDX(fs->object->backing_object_offset);
1258                 next_object = fs->object->backing_object;
1259                 if (next_object == NULL) {
1260                         /*
1261                          * If there's no object left, fill the page in the top
1262                          * object with zeros.
1263                          */
1264                         if (fs->object != fs->first_object) {
1265                                 vm_object_pip_wakeup(fs->object);
1266
1267                                 fs->object = fs->first_object;
1268                                 pindex = first_pindex;
1269                                 fs->m = fs->first_m;
1270                         }
1271                         fs->first_m = NULL;
1272
1273                         /*
1274                          * Zero the page if necessary and mark it valid.
1275                          */
1276                         if ((fs->m->flags & PG_ZERO) == 0) {
1277                                 vm_page_zero_fill(fs->m);
1278                         } else {
1279                                 mycpu->gd_cnt.v_ozfod++;
1280                         }
1281                         mycpu->gd_cnt.v_zfod++;
1282                         fs->m->valid = VM_PAGE_BITS_ALL;
1283                         break;  /* break to PAGE HAS BEEN FOUND */
1284                 } else {
1285                         if (fs->object != fs->first_object) {
1286                                 vm_object_pip_wakeup(fs->object);
1287                         }
1288                         KASSERT(fs->object != next_object, ("object loop %p", next_object));
1289                         fs->object = next_object;
1290                         vm_object_pip_add(fs->object, 1);
1291                 }
1292         }
1293
1294         /*
1295          * PAGE HAS BEEN FOUND. [Loop invariant still holds -- the object lock
1296          * is held.]
1297          *
1298          * If the page is being written, but isn't already owned by the
1299          * top-level object, we have to copy it into a new page owned by the
1300          * top-level object.
1301          */
1302         KASSERT((fs->m->flags & PG_BUSY) != 0,
1303                 ("vm_fault: not busy after main loop"));
1304
1305         if (fs->object != fs->first_object) {
1306                 /*
1307                  * We only really need to copy if we want to write it.
1308                  */
1309                 if (fault_type & VM_PROT_WRITE) {
1310                         /*
1311                          * This allows pages to be virtually copied from a
1312                          * backing_object into the first_object, where the
1313                          * backing object has no other refs to it, and cannot
1314                          * gain any more refs.  Instead of a bcopy, we just
1315                          * move the page from the backing object to the
1316                          * first object.  Note that we must mark the page
1317                          * dirty in the first object so that it will go out
1318                          * to swap when needed.
1319                          */
1320                         if (
1321                                 /*
1322                                  * Map, if present, has not changed
1323                                  */
1324                                 (fs->map == NULL ||
1325                                 fs->map_generation == fs->map->timestamp) &&
1326                                 /*
1327                                  * Only one shadow object
1328                                  */
1329                                 (fs->object->shadow_count == 1) &&
1330                                 /*
1331                                  * No COW refs, except us
1332                                  */
1333                                 (fs->object->ref_count == 1) &&
1334                                 /*
1335                                  * No one else can look this object up
1336                                  */
1337                                 (fs->object->handle == NULL) &&
1338                                 /*
1339                                  * No other ways to look the object up
1340                                  */
1341                                 ((fs->object->type == OBJT_DEFAULT) ||
1342                                  (fs->object->type == OBJT_SWAP)) &&
1343                                 /*
1344                                  * We don't chase down the shadow chain
1345                                  */
1346                                 (fs->object == fs->first_object->backing_object) &&
1347
1348                                 /*
1349                                  * grab the lock if we need to
1350                                  */
1351                                 (fs->lookup_still_valid ||
1352                                  fs->map == NULL ||
1353                                  lockmgr(&fs->map->lock, LK_EXCLUSIVE|LK_NOWAIT) == 0)
1354                             ) {
1355
1356                                 fs->lookup_still_valid = 1;
1357                                 /*
1358                                  * get rid of the unnecessary page
1359                                  */
1360                                 vm_page_protect(fs->first_m, VM_PROT_NONE);
1361                                 vm_page_free(fs->first_m);
1362                                 fs->first_m = NULL;
1363
1364                                 /*
1365                                  * grab the page and put it into the
1366                                  * process'es object.  The page is
1367                                  * automatically made dirty.
1368                                  */
1369                                 vm_page_rename(fs->m, fs->first_object, first_pindex);
1370                                 fs->first_m = fs->m;
1371                                 vm_page_busy(fs->first_m);
1372                                 fs->m = NULL;
1373                                 mycpu->gd_cnt.v_cow_optim++;
1374                         } else {
1375                                 /*
1376                                  * Oh, well, lets copy it.
1377                                  */
1378                                 vm_page_copy(fs->m, fs->first_m);
1379                                 vm_page_event(fs->m, VMEVENT_COW);
1380                         }
1381
1382                         if (fs->m) {
1383                                 /*
1384                                  * We no longer need the old page or object.
1385                                  */
1386                                 release_page(fs);
1387                         }
1388
1389                         /*
1390                          * fs->object != fs->first_object due to above
1391                          * conditional
1392                          */
1393                         vm_object_pip_wakeup(fs->object);
1394
1395                         /*
1396                          * Only use the new page below...
1397                          */
1398
1399                         mycpu->gd_cnt.v_cow_faults++;
1400                         fs->m = fs->first_m;
1401                         fs->object = fs->first_object;
1402                         pindex = first_pindex;
1403                 } else {
1404                         /*
1405                          * If it wasn't a write fault avoid having to copy
1406                          * the page by mapping it read-only.
1407                          */
1408                         fs->prot &= ~VM_PROT_WRITE;
1409                 }
1410         }
1411
1412         /*
1413          * We may have had to unlock a map to do I/O.  If we did then
1414          * lookup_still_valid will be FALSE.  If the map generation count
1415          * also changed then all sorts of things could have happened while
1416          * we were doing the I/O and we need to retry.
1417          */
1418
1419         if (!fs->lookup_still_valid &&
1420             fs->map != NULL &&
1421             (fs->map->timestamp != fs->map_generation)) {
1422                 release_page(fs);
1423                 unlock_and_deallocate(fs);
1424                 return (KERN_TRY_AGAIN);
1425         }
1426
1427         /*
1428          * If the fault is a write, we know that this page is being
1429          * written NOW so dirty it explicitly to save on pmap_is_modified()
1430          * calls later.
1431          *
1432          * If this is a NOSYNC mmap we do not want to set PG_NOSYNC
1433          * if the page is already dirty to prevent data written with
1434          * the expectation of being synced from not being synced.
1435          * Likewise if this entry does not request NOSYNC then make
1436          * sure the page isn't marked NOSYNC.  Applications sharing
1437          * data should use the same flags to avoid ping ponging.
1438          *
1439          * Also tell the backing pager, if any, that it should remove
1440          * any swap backing since the page is now dirty.
1441          */
1442         if (fs->prot & VM_PROT_WRITE) {
1443                 vm_object_set_writeable_dirty(fs->m->object);
1444                 if (fs->entry->eflags & MAP_ENTRY_NOSYNC) {
1445                         if (fs->m->dirty == 0)
1446                                 vm_page_flag_set(fs->m, PG_NOSYNC);
1447                 } else {
1448                         vm_page_flag_clear(fs->m, PG_NOSYNC);
1449                 }
1450                 if (fs->fault_flags & VM_FAULT_DIRTY) {
1451                         crit_enter();
1452                         vm_page_dirty(fs->m);
1453                         vm_pager_page_unswapped(fs->m);
1454                         crit_exit();
1455                 }
1456         }
1457
1458         /*
1459          * Page had better still be busy.  We are still locked up and
1460          * fs->object will have another PIP reference if it is not equal
1461          * to fs->first_object.
1462          */
1463         KASSERT(fs->m->flags & PG_BUSY,
1464                 ("vm_fault: page %p not busy!", fs->m));
1465
1466         /*
1467          * Sanity check: page must be completely valid or it is not fit to
1468          * map into user space.  vm_pager_get_pages() ensures this.
1469          */
1470         if (fs->m->valid != VM_PAGE_BITS_ALL) {
1471                 vm_page_zero_invalid(fs->m, TRUE);
1472                 kprintf("Warning: page %p partially invalid on fault\n", fs->m);
1473         }
1474
1475         return (KERN_SUCCESS);
1476 }
1477
1478 /*
1479  * Wire down a range of virtual addresses in a map.  The entry in question
1480  * should be marked in-transition and the map must be locked.  We must
1481  * release the map temporarily while faulting-in the page to avoid a
1482  * deadlock.  Note that the entry may be clipped while we are blocked but
1483  * will never be freed.
1484  */
1485 int
1486 vm_fault_wire(vm_map_t map, vm_map_entry_t entry, boolean_t user_wire)
1487 {
1488         boolean_t fictitious;
1489         vm_offset_t start;
1490         vm_offset_t end;
1491         vm_offset_t va;
1492         vm_paddr_t pa;
1493         pmap_t pmap;
1494         int rv;
1495
1496         pmap = vm_map_pmap(map);
1497         start = entry->start;
1498         end = entry->end;
1499         fictitious = entry->object.vm_object &&
1500                         (entry->object.vm_object->type == OBJT_DEVICE);
1501
1502         vm_map_unlock(map);
1503         map->timestamp++;
1504
1505         /*
1506          * We simulate a fault to get the page and enter it in the physical
1507          * map.
1508          */
1509         for (va = start; va < end; va += PAGE_SIZE) {
1510                 if (user_wire) {
1511                         rv = vm_fault(map, va, VM_PROT_READ,
1512                                         VM_FAULT_USER_WIRE);
1513                 } else {
1514                         rv = vm_fault(map, va, VM_PROT_READ|VM_PROT_WRITE,
1515                                         VM_FAULT_CHANGE_WIRING);
1516                 }
1517                 if (rv) {
1518                         while (va > start) {
1519                                 va -= PAGE_SIZE;
1520                                 if ((pa = pmap_extract(pmap, va)) == 0)
1521                                         continue;
1522                                 pmap_change_wiring(pmap, va, FALSE);
1523                                 if (!fictitious)
1524                                         vm_page_unwire(PHYS_TO_VM_PAGE(pa), 1);
1525                         }
1526                         vm_map_lock(map);
1527                         return (rv);
1528                 }
1529         }
1530         vm_map_lock(map);
1531         return (KERN_SUCCESS);
1532 }
1533
1534 /*
1535  * Unwire a range of virtual addresses in a map.  The map should be
1536  * locked.
1537  */
1538 void
1539 vm_fault_unwire(vm_map_t map, vm_map_entry_t entry)
1540 {
1541         boolean_t fictitious;
1542         vm_offset_t start;
1543         vm_offset_t end;
1544         vm_offset_t va;
1545         vm_paddr_t pa;
1546         pmap_t pmap;
1547
1548         pmap = vm_map_pmap(map);
1549         start = entry->start;
1550         end = entry->end;
1551         fictitious = entry->object.vm_object &&
1552                         (entry->object.vm_object->type == OBJT_DEVICE);
1553
1554         /*
1555          * Since the pages are wired down, we must be able to get their
1556          * mappings from the physical map system.
1557          */
1558         for (va = start; va < end; va += PAGE_SIZE) {
1559                 pa = pmap_extract(pmap, va);
1560                 if (pa != 0) {
1561                         pmap_change_wiring(pmap, va, FALSE);
1562                         if (!fictitious)
1563                                 vm_page_unwire(PHYS_TO_VM_PAGE(pa), 1);
1564                 }
1565         }
1566 }
1567
1568 /*
1569  * Reduce the rate at which memory is allocated to a process based
1570  * on the perceived load on the VM system. As the load increases
1571  * the allocation burst rate goes down and the delay increases.
1572  *
1573  * Rate limiting does not apply when faulting active or inactive
1574  * pages.  When faulting 'cache' pages, rate limiting only applies
1575  * if the system currently has a severe page deficit.
1576  *
1577  * XXX vm_pagesupply should be increased when a page is freed.
1578  *
1579  * We sleep up to 1/10 of a second.
1580  */
1581 static int
1582 vm_fault_ratelimit(struct vmspace *vmspace)
1583 {
1584         if (vm_load_enable == 0)
1585                 return(0);
1586         if (vmspace->vm_pagesupply > 0) {
1587                 --vmspace->vm_pagesupply;
1588                 return(0);
1589         }
1590 #ifdef INVARIANTS
1591         if (vm_load_debug) {
1592                 kprintf("load %-4d give %d pgs, wait %d, pid %-5d (%s)\n",
1593                         vm_load,
1594                         (1000 - vm_load ) / 10, vm_load * hz / 10000,
1595                         curproc->p_pid, curproc->p_comm);
1596         }
1597 #endif
1598         vmspace->vm_pagesupply = (1000 - vm_load) / 10;
1599         return(vm_load * hz / 10000);
1600 }
1601
1602 /*
1603  *      Routine:
1604  *              vm_fault_copy_entry
1605  *      Function:
1606  *              Copy all of the pages from a wired-down map entry to another.
1607  *
1608  *      In/out conditions:
1609  *              The source and destination maps must be locked for write.
1610  *              The source map entry must be wired down (or be a sharing map
1611  *              entry corresponding to a main map entry that is wired down).
1612  */
1613
1614 void
1615 vm_fault_copy_entry(vm_map_t dst_map, vm_map_t src_map,
1616     vm_map_entry_t dst_entry, vm_map_entry_t src_entry)
1617 {
1618         vm_object_t dst_object;
1619         vm_object_t src_object;
1620         vm_ooffset_t dst_offset;
1621         vm_ooffset_t src_offset;
1622         vm_prot_t prot;
1623         vm_offset_t vaddr;
1624         vm_page_t dst_m;
1625         vm_page_t src_m;
1626
1627 #ifdef  lint
1628         src_map++;
1629 #endif  /* lint */
1630
1631         src_object = src_entry->object.vm_object;
1632         src_offset = src_entry->offset;
1633
1634         /*
1635          * Create the top-level object for the destination entry. (Doesn't
1636          * actually shadow anything - we copy the pages directly.)
1637          */
1638         vm_map_entry_allocate_object(dst_entry);
1639         dst_object = dst_entry->object.vm_object;
1640
1641         prot = dst_entry->max_protection;
1642
1643         /*
1644          * Loop through all of the pages in the entry's range, copying each
1645          * one from the source object (it should be there) to the destination
1646          * object.
1647          */
1648         for (vaddr = dst_entry->start, dst_offset = 0;
1649             vaddr < dst_entry->end;
1650             vaddr += PAGE_SIZE, dst_offset += PAGE_SIZE) {
1651
1652                 /*
1653                  * Allocate a page in the destination object
1654                  */
1655                 do {
1656                         dst_m = vm_page_alloc(dst_object,
1657                                 OFF_TO_IDX(dst_offset), VM_ALLOC_NORMAL);
1658                         if (dst_m == NULL) {
1659                                 vm_wait(0);
1660                         }
1661                 } while (dst_m == NULL);
1662
1663                 /*
1664                  * Find the page in the source object, and copy it in.
1665                  * (Because the source is wired down, the page will be in
1666                  * memory.)
1667                  */
1668                 src_m = vm_page_lookup(src_object,
1669                         OFF_TO_IDX(dst_offset + src_offset));
1670                 if (src_m == NULL)
1671                         panic("vm_fault_copy_wired: page missing");
1672
1673                 vm_page_copy(src_m, dst_m);
1674                 vm_page_event(src_m, VMEVENT_COW);
1675
1676                 /*
1677                  * Enter it in the pmap...
1678                  */
1679
1680                 vm_page_flag_clear(dst_m, PG_ZERO);
1681                 pmap_enter(dst_map->pmap, vaddr, dst_m, prot, FALSE);
1682
1683                 /*
1684                  * Mark it no longer busy, and put it on the active list.
1685                  */
1686                 vm_page_activate(dst_m);
1687                 vm_page_wakeup(dst_m);
1688         }
1689 }
1690
1691 #if 0
1692
1693 /*
1694  * This routine checks around the requested page for other pages that
1695  * might be able to be faulted in.  This routine brackets the viable
1696  * pages for the pages to be paged in.
1697  *
1698  * Inputs:
1699  *      m, rbehind, rahead
1700  *
1701  * Outputs:
1702  *  marray (array of vm_page_t), reqpage (index of requested page)
1703  *
1704  * Return value:
1705  *  number of pages in marray
1706  */
1707 static int
1708 vm_fault_additional_pages(vm_page_t m, int rbehind, int rahead,
1709                           vm_page_t *marray, int *reqpage)
1710 {
1711         int i,j;
1712         vm_object_t object;
1713         vm_pindex_t pindex, startpindex, endpindex, tpindex;
1714         vm_page_t rtm;
1715         int cbehind, cahead;
1716
1717         object = m->object;
1718         pindex = m->pindex;
1719
1720         /*
1721          * we don't fault-ahead for device pager
1722          */
1723         if (object->type == OBJT_DEVICE) {
1724                 *reqpage = 0;
1725                 marray[0] = m;
1726                 return 1;
1727         }
1728
1729         /*
1730          * if the requested page is not available, then give up now
1731          */
1732         if (!vm_pager_has_page(object, pindex, &cbehind, &cahead)) {
1733                 *reqpage = 0;   /* not used by caller, fix compiler warn */
1734                 return 0;
1735         }
1736
1737         if ((cbehind == 0) && (cahead == 0)) {
1738                 *reqpage = 0;
1739                 marray[0] = m;
1740                 return 1;
1741         }
1742
1743         if (rahead > cahead) {
1744                 rahead = cahead;
1745         }
1746
1747         if (rbehind > cbehind) {
1748                 rbehind = cbehind;
1749         }
1750
1751         /*
1752          * Do not do any readahead if we have insufficient free memory.
1753          *
1754          * XXX code was broken disabled before and has instability
1755          * with this conditonal fixed, so shortcut for now.
1756          */
1757         if (burst_fault == 0 || vm_page_count_severe()) {
1758                 marray[0] = m;
1759                 *reqpage = 0;
1760                 return 1;
1761         }
1762
1763         /*
1764          * scan backward for the read behind pages -- in memory
1765          *
1766          * Assume that if the page is not found an interrupt will not
1767          * create it.  Theoretically interrupts can only remove (busy)
1768          * pages, not create new associations.
1769          */
1770         if (pindex > 0) {
1771                 if (rbehind > pindex) {
1772                         rbehind = pindex;
1773                         startpindex = 0;
1774                 } else {
1775                         startpindex = pindex - rbehind;
1776                 }
1777
1778                 crit_enter();
1779                 for (tpindex = pindex; tpindex > startpindex; --tpindex) {
1780                         if (vm_page_lookup(object, tpindex - 1))
1781                                 break;
1782                 }
1783
1784                 i = 0;
1785                 while (tpindex < pindex) {
1786                         rtm = vm_page_alloc(object, tpindex, VM_ALLOC_SYSTEM);
1787                         if (rtm == NULL) {
1788                                 crit_exit();
1789                                 for (j = 0; j < i; j++) {
1790                                         vm_page_free(marray[j]);
1791                                 }
1792                                 marray[0] = m;
1793                                 *reqpage = 0;
1794                                 return 1;
1795                         }
1796                         marray[i] = rtm;
1797                         ++i;
1798                         ++tpindex;
1799                 }
1800                 crit_exit();
1801         } else {
1802                 i = 0;
1803         }
1804
1805         /*
1806          * Assign requested page
1807          */
1808         marray[i] = m;
1809         *reqpage = i;
1810         ++i;
1811
1812         /*
1813          * Scan forwards for read-ahead pages
1814          */
1815         tpindex = pindex + 1;
1816         endpindex = tpindex + rahead;
1817         if (endpindex > object->size)
1818                 endpindex = object->size;
1819
1820         crit_enter();
1821         while (tpindex < endpindex) {
1822                 if (vm_page_lookup(object, tpindex))
1823                         break;
1824                 rtm = vm_page_alloc(object, tpindex, VM_ALLOC_SYSTEM);
1825                 if (rtm == NULL)
1826                         break;
1827                 marray[i] = rtm;
1828                 ++i;
1829                 ++tpindex;
1830         }
1831         crit_exit();
1832
1833         return (i);
1834 }
1835
1836 #endif
1837
1838 /*
1839  * vm_prefault() provides a quick way of clustering pagefaults into a
1840  * processes address space.  It is a "cousin" of pmap_object_init_pt,
1841  * except it runs at page fault time instead of mmap time.
1842  *
1843  * This code used to be per-platform pmap_prefault().  It is now
1844  * machine-independent and enhanced to also pre-fault zero-fill pages
1845  * (see vm.fast_fault) as well as make them writable, which greatly
1846  * reduces the number of page faults programs incur.
1847  *
1848  * Application performance when pre-faulting zero-fill pages is heavily
1849  * dependent on the application.  Very tiny applications like /bin/echo
1850  * lose a little performance while applications of any appreciable size
1851  * gain performance.  Prefaulting multiple pages also reduces SMP
1852  * congestion and can improve SMP performance significantly.
1853  *
1854  * NOTE!  prot may allow writing but this only applies to the top level
1855  *        object.  If we wind up mapping a page extracted from a backing
1856  *        object we have to make sure it is read-only.
1857  *
1858  * NOTE!  The caller has already handled any COW operations on the
1859  *        vm_map_entry via the normal fault code.  Do NOT call this
1860  *        shortcut unless the normal fault code has run on this entry.
1861  */
1862 #define PFBAK 4
1863 #define PFFOR 4
1864 #define PAGEORDER_SIZE (PFBAK+PFFOR)
1865
1866 static int vm_prefault_pageorder[] = {
1867         -PAGE_SIZE, PAGE_SIZE,
1868         -2 * PAGE_SIZE, 2 * PAGE_SIZE,
1869         -3 * PAGE_SIZE, 3 * PAGE_SIZE,
1870         -4 * PAGE_SIZE, 4 * PAGE_SIZE
1871 };
1872
1873 static void
1874 vm_prefault(pmap_t pmap, vm_offset_t addra, vm_map_entry_t entry, int prot)
1875 {
1876         struct lwp *lp;
1877         vm_page_t m;
1878         vm_offset_t starta;
1879         vm_offset_t addr;
1880         vm_pindex_t index;
1881         vm_pindex_t pindex;
1882         vm_object_t object;
1883         int pprot;
1884         int i;
1885
1886         /*
1887          * We do not currently prefault mappings that use virtual page
1888          * tables.  We do not prefault foreign pmaps.
1889          */
1890         if (entry->maptype == VM_MAPTYPE_VPAGETABLE)
1891                 return;
1892         lp = curthread->td_lwp;
1893         if (lp == NULL || (pmap != vmspace_pmap(lp->lwp_vmspace)))
1894                 return;
1895
1896         object = entry->object.vm_object;
1897
1898         starta = addra - PFBAK * PAGE_SIZE;
1899         if (starta < entry->start)
1900                 starta = entry->start;
1901         else if (starta > addra)
1902                 starta = 0;
1903
1904         /*
1905          * critical section protection is required to maintain the
1906          * page/object association, interrupts can free pages and remove
1907          * them from their objects.
1908          */
1909         crit_enter();
1910         for (i = 0; i < PAGEORDER_SIZE; i++) {
1911                 vm_object_t lobject;
1912
1913                 addr = addra + vm_prefault_pageorder[i];
1914                 if (addr > addra + (PFFOR * PAGE_SIZE))
1915                         addr = 0;
1916
1917                 if (addr < starta || addr >= entry->end)
1918                         continue;
1919
1920                 if (pmap_prefault_ok(pmap, addr) == 0)
1921                         continue;
1922
1923                 /*
1924                  * Follow the VM object chain to obtain the page to be mapped
1925                  * into the pmap.
1926                  *
1927                  * If we reach the terminal object without finding a page
1928                  * and we determine it would be advantageous, then allocate
1929                  * a zero-fill page for the base object.  The base object
1930                  * is guaranteed to be OBJT_DEFAULT for this case.
1931                  */
1932                 index = ((addr - entry->start) + entry->offset) >> PAGE_SHIFT;
1933                 lobject = object;
1934                 pindex = index;
1935                 pprot = prot;
1936
1937                 while ((m = vm_page_lookup(lobject, pindex)) == NULL) {
1938                         if (lobject->type != OBJT_DEFAULT)
1939                                 break;
1940                         if (lobject->backing_object == NULL) {
1941                                 if (vm_fast_fault == 0)
1942                                         break;
1943                                 if (vm_prefault_pageorder[i] < 0 ||
1944                                     (prot & VM_PROT_WRITE) == 0 ||
1945                                     vm_page_count_min(0)) {
1946                                         break;
1947                                 }
1948                                 m = vm_page_alloc(object, index,
1949                                               VM_ALLOC_NORMAL | VM_ALLOC_ZERO);
1950
1951                                 if ((m->flags & PG_ZERO) == 0) {
1952                                         vm_page_zero_fill(m);
1953                                 } else {
1954                                         vm_page_flag_clear(m, PG_ZERO);
1955                                         mycpu->gd_cnt.v_ozfod++;
1956                                 }
1957                                 mycpu->gd_cnt.v_zfod++;
1958                                 m->valid = VM_PAGE_BITS_ALL;
1959                                 vm_page_wakeup(m);
1960                                 pprot = prot;
1961                                 /* lobject = object .. not needed */
1962                                 break;
1963                         }
1964                         if (lobject->backing_object_offset & PAGE_MASK)
1965                                 break;
1966                         pindex += lobject->backing_object_offset >> PAGE_SHIFT;
1967                         lobject = lobject->backing_object;
1968                         pprot &= ~VM_PROT_WRITE;
1969                 }
1970                 /*
1971                  * NOTE: lobject now invalid (if we did a zero-fill we didn't
1972                  *       bother assigning lobject = object).
1973                  *
1974                  * Give-up if the page is not available.
1975                  */
1976                 if (m == NULL)
1977                         break;
1978
1979                 /*
1980                  * Do not conditionalize on PG_RAM.  If pages are present in
1981                  * the VM system we assume optimal caching.  If caching is
1982                  * not optimal the I/O gravy train will be restarted when we
1983                  * hit an unavailable page.  We do not want to try to restart
1984                  * the gravy train now because we really don't know how much
1985                  * of the object has been cached.  The cost for restarting
1986                  * the gravy train should be low (since accesses will likely
1987                  * be I/O bound anyway).
1988                  *
1989                  * The object must be marked dirty if we are mapping a
1990                  * writable page.
1991                  */
1992                 if (pprot & VM_PROT_WRITE)
1993                         vm_object_set_writeable_dirty(m->object);
1994
1995                 /*
1996                  * Enter the page into the pmap if appropriate.
1997                  */
1998                 if (((m->valid & VM_PAGE_BITS_ALL) == VM_PAGE_BITS_ALL) &&
1999                     (m->busy == 0) &&
2000                     (m->flags & (PG_BUSY | PG_FICTITIOUS)) == 0) {
2001
2002                         if ((m->queue - m->pc) == PQ_CACHE) {
2003                                 vm_page_deactivate(m);
2004                         }
2005                         vm_page_busy(m);
2006                         pmap_enter(pmap, addr, m, pprot, 0);
2007                         vm_page_wakeup(m);
2008                 }
2009         }
2010         crit_exit();
2011 }