The Design and Implementation of the FreeBSD Operating System, Second Edition
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FreeBSD/Linux Kernel Cross Reference
sys/vm/vm_fault.c

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    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 
   70 /*
   71  *      Page fault handling module.
   72  */
   73 
   74 #include <sys/cdefs.h>
   75 __FBSDID("$FreeBSD: releng/8.2/sys/vm/vm_fault.c 215430 2010-11-17 17:29:22Z alc $");
   76 
   77 #include "opt_vm.h"
   78 
   79 #include <sys/param.h>
   80 #include <sys/systm.h>
   81 #include <sys/kernel.h>
   82 #include <sys/lock.h>
   83 #include <sys/mutex.h>
   84 #include <sys/proc.h>
   85 #include <sys/resourcevar.h>
   86 #include <sys/sysctl.h>
   87 #include <sys/vmmeter.h>
   88 #include <sys/vnode.h>
   89 
   90 #include <vm/vm.h>
   91 #include <vm/vm_param.h>
   92 #include <vm/pmap.h>
   93 #include <vm/vm_map.h>
   94 #include <vm/vm_object.h>
   95 #include <vm/vm_page.h>
   96 #include <vm/vm_pageout.h>
   97 #include <vm/vm_kern.h>
   98 #include <vm/vm_pager.h>
   99 #include <vm/vnode_pager.h>
  100 #include <vm/vm_extern.h>
  101 
  102 #include <sys/mount.h>  /* XXX Temporary for VFS_LOCK_GIANT() */
  103 
  104 #define PFBAK 4
  105 #define PFFOR 4
  106 #define PAGEORDER_SIZE (PFBAK+PFFOR)
  107 
  108 static int prefault_pageorder[] = {
  109         -1 * PAGE_SIZE, 1 * PAGE_SIZE,
  110         -2 * PAGE_SIZE, 2 * PAGE_SIZE,
  111         -3 * PAGE_SIZE, 3 * PAGE_SIZE,
  112         -4 * PAGE_SIZE, 4 * PAGE_SIZE
  113 };
  114 
  115 static int vm_fault_additional_pages(vm_page_t, int, int, vm_page_t *, int *);
  116 static void vm_fault_prefault(pmap_t, vm_offset_t, vm_map_entry_t);
  117 
  118 #define VM_FAULT_READ_AHEAD 8
  119 #define VM_FAULT_READ_BEHIND 7
  120 #define VM_FAULT_READ (VM_FAULT_READ_AHEAD+VM_FAULT_READ_BEHIND+1)
  121 
  122 struct faultstate {
  123         vm_page_t m;
  124         vm_object_t object;
  125         vm_pindex_t pindex;
  126         vm_page_t first_m;
  127         vm_object_t     first_object;
  128         vm_pindex_t first_pindex;
  129         vm_map_t map;
  130         vm_map_entry_t entry;
  131         int lookup_still_valid;
  132         struct vnode *vp;
  133         int vfslocked;
  134 };
  135 
  136 static inline void
  137 release_page(struct faultstate *fs)
  138 {
  139 
  140         vm_page_wakeup(fs->m);
  141         vm_page_lock_queues();
  142         vm_page_deactivate(fs->m);
  143         vm_page_unlock_queues();
  144         fs->m = NULL;
  145 }
  146 
  147 static inline void
  148 unlock_map(struct faultstate *fs)
  149 {
  150 
  151         if (fs->lookup_still_valid) {
  152                 vm_map_lookup_done(fs->map, fs->entry);
  153                 fs->lookup_still_valid = FALSE;
  154         }
  155 }
  156 
  157 static void
  158 unlock_and_deallocate(struct faultstate *fs)
  159 {
  160 
  161         vm_object_pip_wakeup(fs->object);
  162         VM_OBJECT_UNLOCK(fs->object);
  163         if (fs->object != fs->first_object) {
  164                 VM_OBJECT_LOCK(fs->first_object);
  165                 vm_page_lock_queues();
  166                 vm_page_free(fs->first_m);
  167                 vm_page_unlock_queues();
  168                 vm_object_pip_wakeup(fs->first_object);
  169                 VM_OBJECT_UNLOCK(fs->first_object);
  170                 fs->first_m = NULL;
  171         }
  172         vm_object_deallocate(fs->first_object);
  173         unlock_map(fs); 
  174         if (fs->vp != NULL) { 
  175                 vput(fs->vp);
  176                 fs->vp = NULL;
  177         }
  178         VFS_UNLOCK_GIANT(fs->vfslocked);
  179         fs->vfslocked = 0;
  180 }
  181 
  182 /*
  183  * TRYPAGER - used by vm_fault to calculate whether the pager for the
  184  *            current object *might* contain the page.
  185  *
  186  *            default objects are zero-fill, there is no real pager.
  187  */
  188 #define TRYPAGER        (fs.object->type != OBJT_DEFAULT && \
  189                         (((fault_flags & VM_FAULT_WIRE_MASK) == 0) || wired))
  190 
  191 /*
  192  *      vm_fault:
  193  *
  194  *      Handle a page fault occurring at the given address,
  195  *      requiring the given permissions, in the map specified.
  196  *      If successful, the page is inserted into the
  197  *      associated physical map.
  198  *
  199  *      NOTE: the given address should be truncated to the
  200  *      proper page address.
  201  *
  202  *      KERN_SUCCESS is returned if the page fault is handled; otherwise,
  203  *      a standard error specifying why the fault is fatal is returned.
  204  *
  205  *
  206  *      The map in question must be referenced, and remains so.
  207  *      Caller may hold no locks.
  208  */
  209 int
  210 vm_fault(vm_map_t map, vm_offset_t vaddr, vm_prot_t fault_type,
  211          int fault_flags)
  212 {
  213         vm_prot_t prot;
  214         int is_first_object_locked, result;
  215         boolean_t are_queues_locked, growstack, wired;
  216         int map_generation;
  217         vm_object_t next_object;
  218         vm_page_t marray[VM_FAULT_READ], mt, mt_prev;
  219         int hardfault;
  220         int faultcount, ahead, behind, alloc_req;
  221         struct faultstate fs;
  222         struct vnode *vp;
  223         int locked, error;
  224 
  225         hardfault = 0;
  226         growstack = TRUE;
  227         PCPU_INC(cnt.v_vm_faults);
  228         fs.vp = NULL;
  229         fs.vfslocked = 0;
  230         faultcount = behind = 0;
  231 
  232 RetryFault:;
  233 
  234         /*
  235          * Find the backing store object and offset into it to begin the
  236          * search.
  237          */
  238         fs.map = map;
  239         result = vm_map_lookup(&fs.map, vaddr, fault_type, &fs.entry,
  240             &fs.first_object, &fs.first_pindex, &prot, &wired);
  241         if (result != KERN_SUCCESS) {
  242                 if (result != KERN_PROTECTION_FAILURE ||
  243                     (fault_flags & VM_FAULT_WIRE_MASK) != VM_FAULT_USER_WIRE) {
  244                         if (growstack && result == KERN_INVALID_ADDRESS &&
  245                             map != kernel_map && curproc != NULL) {
  246                                 result = vm_map_growstack(curproc, vaddr);
  247                                 if (result != KERN_SUCCESS)
  248                                         return (KERN_FAILURE);
  249                                 growstack = FALSE;
  250                                 goto RetryFault;
  251                         }
  252                         return (result);
  253                 }
  254 
  255                 /*
  256                  * If we are user-wiring a r/w segment, and it is COW, then
  257                  * we need to do the COW operation.  Note that we don't COW
  258                  * currently RO sections now, because it is NOT desirable
  259                  * to COW .text.  We simply keep .text from ever being COW'ed
  260                  * and take the heat that one cannot debug wired .text sections.
  261                  */
  262                 result = vm_map_lookup(&fs.map, vaddr,
  263                         VM_PROT_READ|VM_PROT_WRITE|VM_PROT_OVERRIDE_WRITE,
  264                         &fs.entry, &fs.first_object, &fs.first_pindex, &prot, &wired);
  265                 if (result != KERN_SUCCESS)
  266                         return (result);
  267 
  268                 /*
  269                  * If we don't COW now, on a user wire, the user will never
  270                  * be able to write to the mapping.  If we don't make this
  271                  * restriction, the bookkeeping would be nearly impossible.
  272                  *
  273                  * XXX The following assignment modifies the map without
  274                  * holding a write lock on it.
  275                  */
  276                 if ((fs.entry->protection & VM_PROT_WRITE) == 0)
  277                         fs.entry->max_protection &= ~VM_PROT_WRITE;
  278         }
  279 
  280         map_generation = fs.map->timestamp;
  281 
  282         if (fs.entry->eflags & MAP_ENTRY_NOFAULT) {
  283                 panic("vm_fault: fault on nofault entry, addr: %lx",
  284                     (u_long)vaddr);
  285         }
  286 
  287         /*
  288          * Make a reference to this object to prevent its disposal while we
  289          * are messing with it.  Once we have the reference, the map is free
  290          * to be diddled.  Since objects reference their shadows (and copies),
  291          * they will stay around as well.
  292          *
  293          * Bump the paging-in-progress count to prevent size changes (e.g. 
  294          * truncation operations) during I/O.  This must be done after
  295          * obtaining the vnode lock in order to avoid possible deadlocks.
  296          */
  297         VM_OBJECT_LOCK(fs.first_object);
  298         vm_object_reference_locked(fs.first_object);
  299         vm_object_pip_add(fs.first_object, 1);
  300 
  301         fs.lookup_still_valid = TRUE;
  302 
  303         if (wired)
  304                 fault_type = prot;
  305 
  306         fs.first_m = NULL;
  307 
  308         /*
  309          * Search for the page at object/offset.
  310          */
  311         fs.object = fs.first_object;
  312         fs.pindex = fs.first_pindex;
  313         while (TRUE) {
  314                 /*
  315                  * If the object is dead, we stop here
  316                  */
  317                 if (fs.object->flags & OBJ_DEAD) {
  318                         unlock_and_deallocate(&fs);
  319                         return (KERN_PROTECTION_FAILURE);
  320                 }
  321 
  322                 /*
  323                  * See if page is resident
  324                  */
  325                 fs.m = vm_page_lookup(fs.object, fs.pindex);
  326                 if (fs.m != NULL) {
  327                         /* 
  328                          * check for page-based copy on write.
  329                          * We check fs.object == fs.first_object so
  330                          * as to ensure the legacy COW mechanism is
  331                          * used when the page in question is part of
  332                          * a shadow object.  Otherwise, vm_page_cowfault()
  333                          * removes the page from the backing object, 
  334                          * which is not what we want.
  335                          */
  336                         vm_page_lock_queues();
  337                         if ((fs.m->cow) && 
  338                             (fault_type & VM_PROT_WRITE) &&
  339                             (fs.object == fs.first_object)) {
  340                                 vm_page_cowfault(fs.m);
  341                                 vm_page_unlock_queues();
  342                                 unlock_and_deallocate(&fs);
  343                                 goto RetryFault;
  344                         }
  345 
  346                         /*
  347                          * Wait/Retry if the page is busy.  We have to do this
  348                          * if the page is busy via either VPO_BUSY or 
  349                          * vm_page_t->busy because the vm_pager may be using
  350                          * vm_page_t->busy for pageouts ( and even pageins if
  351                          * it is the vnode pager ), and we could end up trying
  352                          * to pagein and pageout the same page simultaneously.
  353                          *
  354                          * We can theoretically allow the busy case on a read
  355                          * fault if the page is marked valid, but since such
  356                          * pages are typically already pmap'd, putting that
  357                          * special case in might be more effort then it is 
  358                          * worth.  We cannot under any circumstances mess
  359                          * around with a vm_page_t->busy page except, perhaps,
  360                          * to pmap it.
  361                          */
  362                         if ((fs.m->oflags & VPO_BUSY) || fs.m->busy) {
  363                                 vm_page_unlock_queues();
  364                                 if (fs.object != fs.first_object) {
  365                                         if (!VM_OBJECT_TRYLOCK(
  366                                             fs.first_object)) {
  367                                                 VM_OBJECT_UNLOCK(fs.object);
  368                                                 VM_OBJECT_LOCK(fs.first_object);
  369                                                 VM_OBJECT_LOCK(fs.object);
  370                                         }
  371                                         vm_page_lock_queues();
  372                                         vm_page_free(fs.first_m);
  373                                         vm_page_unlock_queues();
  374                                         vm_object_pip_wakeup(fs.first_object);
  375                                         VM_OBJECT_UNLOCK(fs.first_object);
  376                                         fs.first_m = NULL;
  377                                 }
  378                                 unlock_map(&fs);
  379                                 if (fs.m == vm_page_lookup(fs.object,
  380                                     fs.pindex)) {
  381                                         vm_page_sleep_if_busy(fs.m, TRUE,
  382                                             "vmpfw");
  383                                 }
  384                                 vm_object_pip_wakeup(fs.object);
  385                                 VM_OBJECT_UNLOCK(fs.object);
  386                                 PCPU_INC(cnt.v_intrans);
  387                                 vm_object_deallocate(fs.first_object);
  388                                 goto RetryFault;
  389                         }
  390                         vm_pageq_remove(fs.m);
  391                         vm_page_unlock_queues();
  392 
  393                         /*
  394                          * Mark page busy for other processes, and the 
  395                          * pagedaemon.  If it still isn't completely valid
  396                          * (readable), jump to readrest, else break-out ( we
  397                          * found the page ).
  398                          */
  399                         vm_page_busy(fs.m);
  400                         if (fs.m->valid != VM_PAGE_BITS_ALL &&
  401                                 fs.m->object != kernel_object && fs.m->object != kmem_object) {
  402                                 goto readrest;
  403                         }
  404 
  405                         break;
  406                 }
  407 
  408                 /*
  409                  * Page is not resident, If this is the search termination
  410                  * or the pager might contain the page, allocate a new page.
  411                  */
  412                 if (TRYPAGER || fs.object == fs.first_object) {
  413                         if (fs.pindex >= fs.object->size) {
  414                                 unlock_and_deallocate(&fs);
  415                                 return (KERN_PROTECTION_FAILURE);
  416                         }
  417 
  418                         /*
  419                          * Allocate a new page for this object/offset pair.
  420                          *
  421                          * Unlocked read of the p_flag is harmless. At
  422                          * worst, the P_KILLED might be not observed
  423                          * there, and allocation can fail, causing
  424                          * restart and new reading of the p_flag.
  425                          */
  426                         fs.m = NULL;
  427                         if (!vm_page_count_severe() || P_KILLED(curproc)) {
  428 #if VM_NRESERVLEVEL > 0
  429                                 if ((fs.object->flags & OBJ_COLORED) == 0) {
  430                                         fs.object->flags |= OBJ_COLORED;
  431                                         fs.object->pg_color = atop(vaddr) -
  432                                             fs.pindex;
  433                                 }
  434 #endif
  435                                 alloc_req = P_KILLED(curproc) ?
  436                                     VM_ALLOC_SYSTEM : VM_ALLOC_NORMAL;
  437                                 if (fs.object->type != OBJT_VNODE &&
  438                                     fs.object->backing_object == NULL)
  439                                         alloc_req |= VM_ALLOC_ZERO;
  440                                 fs.m = vm_page_alloc(fs.object, fs.pindex,
  441                                     alloc_req);
  442                         }
  443                         if (fs.m == NULL) {
  444                                 unlock_and_deallocate(&fs);
  445                                 VM_WAITPFAULT;
  446                                 goto RetryFault;
  447                         } else if (fs.m->valid == VM_PAGE_BITS_ALL)
  448                                 break;
  449                 }
  450 
  451 readrest:
  452                 /*
  453                  * We have found a valid page or we have allocated a new page.
  454                  * The page thus may not be valid or may not be entirely 
  455                  * valid.
  456                  *
  457                  * Attempt to fault-in the page if there is a chance that the
  458                  * pager has it, and potentially fault in additional pages
  459                  * at the same time.
  460                  */
  461                 if (TRYPAGER) {
  462                         int rv;
  463                         int reqpage = 0;
  464                         u_char behavior = vm_map_entry_behavior(fs.entry);
  465 
  466                         if (behavior == MAP_ENTRY_BEHAV_RANDOM ||
  467                             P_KILLED(curproc)) {
  468                                 ahead = 0;
  469                                 behind = 0;
  470                         } else {
  471                                 behind = (vaddr - fs.entry->start) >> PAGE_SHIFT;
  472                                 if (behind > VM_FAULT_READ_BEHIND)
  473                                         behind = VM_FAULT_READ_BEHIND;
  474 
  475                                 ahead = ((fs.entry->end - vaddr) >> PAGE_SHIFT) - 1;
  476                                 if (ahead > VM_FAULT_READ_AHEAD)
  477                                         ahead = VM_FAULT_READ_AHEAD;
  478                         }
  479                         is_first_object_locked = FALSE;
  480                         if ((behavior == MAP_ENTRY_BEHAV_SEQUENTIAL ||
  481                              (behavior != MAP_ENTRY_BEHAV_RANDOM &&
  482                               fs.pindex >= fs.entry->lastr &&
  483                               fs.pindex < fs.entry->lastr + VM_FAULT_READ)) &&
  484                             (fs.first_object == fs.object ||
  485                              (is_first_object_locked = VM_OBJECT_TRYLOCK(fs.first_object))) &&
  486                             fs.first_object->type != OBJT_DEVICE &&
  487                             fs.first_object->type != OBJT_PHYS &&
  488                             fs.first_object->type != OBJT_SG) {
  489                                 vm_pindex_t firstpindex;
  490 
  491                                 if (fs.first_pindex < 2 * VM_FAULT_READ)
  492                                         firstpindex = 0;
  493                                 else
  494                                         firstpindex = fs.first_pindex - 2 * VM_FAULT_READ;
  495                                 mt = fs.first_object != fs.object ?
  496                                     fs.first_m : fs.m;
  497                                 KASSERT(mt != NULL, ("vm_fault: missing mt"));
  498                                 KASSERT((mt->oflags & VPO_BUSY) != 0,
  499                                     ("vm_fault: mt %p not busy", mt));
  500                                 mt_prev = vm_page_prev(mt);
  501 
  502                                 are_queues_locked = FALSE;
  503                                 /*
  504                                  * note: partially valid pages cannot be 
  505                                  * included in the lookahead - NFS piecemeal
  506                                  * writes will barf on it badly.
  507                                  */
  508                                 while ((mt = mt_prev) != NULL &&
  509                                     mt->pindex >= firstpindex &&
  510                                     mt->valid == VM_PAGE_BITS_ALL) {
  511                                         mt_prev = vm_page_prev(mt);
  512                                         if (mt->busy ||
  513                                             (mt->oflags & VPO_BUSY))
  514                                                 continue;
  515                                         if (!are_queues_locked) {
  516                                                 are_queues_locked = TRUE;
  517                                                 vm_page_lock_queues();
  518                                         }
  519                                         if (mt->hold_count ||
  520                                                 mt->wire_count) 
  521                                                 continue;
  522                                         pmap_remove_all(mt);
  523                                         if (mt->dirty) {
  524                                                 vm_page_deactivate(mt);
  525                                         } else {
  526                                                 vm_page_cache(mt);
  527                                         }
  528                                 }
  529                                 if (are_queues_locked)
  530                                         vm_page_unlock_queues();
  531                                 ahead += behind;
  532                                 behind = 0;
  533                         }
  534                         if (is_first_object_locked)
  535                                 VM_OBJECT_UNLOCK(fs.first_object);
  536 
  537                         /*
  538                          * Call the pager to retrieve the data, if any, after
  539                          * releasing the lock on the map.  We hold a ref on
  540                          * fs.object and the pages are VPO_BUSY'd.
  541                          */
  542                         unlock_map(&fs);
  543 
  544 vnode_lock:
  545                         if (fs.object->type == OBJT_VNODE) {
  546                                 vp = fs.object->handle;
  547                                 if (vp == fs.vp)
  548                                         goto vnode_locked;
  549                                 else if (fs.vp != NULL) {
  550                                         vput(fs.vp);
  551                                         fs.vp = NULL;
  552                                 }
  553                                 locked = VOP_ISLOCKED(vp);
  554 
  555                                 if (VFS_NEEDSGIANT(vp->v_mount) && !fs.vfslocked) {
  556                                         fs.vfslocked = 1;
  557                                         if (!mtx_trylock(&Giant)) {
  558                                                 VM_OBJECT_UNLOCK(fs.object);
  559                                                 mtx_lock(&Giant);
  560                                                 VM_OBJECT_LOCK(fs.object);
  561                                                 goto vnode_lock;
  562                                         }
  563                                 }
  564                                 if (locked != LK_EXCLUSIVE)
  565                                         locked = LK_SHARED;
  566                                 /* Do not sleep for vnode lock while fs.m is busy */
  567                                 error = vget(vp, locked | LK_CANRECURSE |
  568                                     LK_NOWAIT, curthread);
  569                                 if (error != 0) {
  570                                         int vfslocked;
  571 
  572                                         vfslocked = fs.vfslocked;
  573                                         fs.vfslocked = 0; /* Keep Giant */
  574                                         vhold(vp);
  575                                         release_page(&fs);
  576                                         unlock_and_deallocate(&fs);
  577                                         error = vget(vp, locked | LK_RETRY |
  578                                             LK_CANRECURSE, curthread);
  579                                         vdrop(vp);
  580                                         fs.vp = vp;
  581                                         fs.vfslocked = vfslocked;
  582                                         KASSERT(error == 0,
  583                                             ("vm_fault: vget failed"));
  584                                         goto RetryFault;
  585                                 }
  586                                 fs.vp = vp;
  587                         }
  588 vnode_locked:
  589                         KASSERT(fs.vp == NULL || !fs.map->system_map,
  590                             ("vm_fault: vnode-backed object mapped by system map"));
  591 
  592                         /*
  593                          * now we find out if any other pages should be paged
  594                          * in at this time this routine checks to see if the
  595                          * pages surrounding this fault reside in the same
  596                          * object as the page for this fault.  If they do,
  597                          * then they are faulted in also into the object.  The
  598                          * array "marray" returned contains an array of
  599                          * vm_page_t structs where one of them is the
  600                          * vm_page_t passed to the routine.  The reqpage
  601                          * return value is the index into the marray for the
  602                          * vm_page_t passed to the routine.
  603                          *
  604                          * fs.m plus the additional pages are VPO_BUSY'd.
  605                          */
  606                         faultcount = vm_fault_additional_pages(
  607                             fs.m, behind, ahead, marray, &reqpage);
  608 
  609                         rv = faultcount ?
  610                             vm_pager_get_pages(fs.object, marray, faultcount,
  611                                 reqpage) : VM_PAGER_FAIL;
  612 
  613                         if (rv == VM_PAGER_OK) {
  614                                 /*
  615                                  * Found the page. Leave it busy while we play
  616                                  * with it.
  617                                  */
  618 
  619                                 /*
  620                                  * Relookup in case pager changed page. Pager
  621                                  * is responsible for disposition of old page
  622                                  * if moved.
  623                                  */
  624                                 fs.m = vm_page_lookup(fs.object, fs.pindex);
  625                                 if (!fs.m) {
  626                                         unlock_and_deallocate(&fs);
  627                                         goto RetryFault;
  628                                 }
  629 
  630                                 hardfault++;
  631                                 break; /* break to PAGE HAS BEEN FOUND */
  632                         }
  633                         /*
  634                          * Remove the bogus page (which does not exist at this
  635                          * object/offset); before doing so, we must get back
  636                          * our object lock to preserve our invariant.
  637                          *
  638                          * Also wake up any other process that may want to bring
  639                          * in this page.
  640                          *
  641                          * If this is the top-level object, we must leave the
  642                          * busy page to prevent another process from rushing
  643                          * past us, and inserting the page in that object at
  644                          * the same time that we are.
  645                          */
  646                         if (rv == VM_PAGER_ERROR)
  647                                 printf("vm_fault: pager read error, pid %d (%s)\n",
  648                                     curproc->p_pid, curproc->p_comm);
  649                         /*
  650                          * Data outside the range of the pager or an I/O error
  651                          */
  652                         /*
  653                          * XXX - the check for kernel_map is a kludge to work
  654                          * around having the machine panic on a kernel space
  655                          * fault w/ I/O error.
  656                          */
  657                         if (((fs.map != kernel_map) && (rv == VM_PAGER_ERROR)) ||
  658                                 (rv == VM_PAGER_BAD)) {
  659                                 vm_page_lock_queues();
  660                                 vm_page_free(fs.m);
  661                                 vm_page_unlock_queues();
  662                                 fs.m = NULL;
  663                                 unlock_and_deallocate(&fs);
  664                                 return ((rv == VM_PAGER_ERROR) ? KERN_FAILURE : KERN_PROTECTION_FAILURE);
  665                         }
  666                         if (fs.object != fs.first_object) {
  667                                 vm_page_lock_queues();
  668                                 vm_page_free(fs.m);
  669                                 vm_page_unlock_queues();
  670                                 fs.m = NULL;
  671                                 /*
  672                                  * XXX - we cannot just fall out at this
  673                                  * point, m has been freed and is invalid!
  674                                  */
  675                         }
  676                 }
  677 
  678                 /*
  679                  * We get here if the object has default pager (or unwiring) 
  680                  * or the pager doesn't have the page.
  681                  */
  682                 if (fs.object == fs.first_object)
  683                         fs.first_m = fs.m;
  684 
  685                 /*
  686                  * Move on to the next object.  Lock the next object before
  687                  * unlocking the current one.
  688                  */
  689                 fs.pindex += OFF_TO_IDX(fs.object->backing_object_offset);
  690                 next_object = fs.object->backing_object;
  691                 if (next_object == NULL) {
  692                         /*
  693                          * If there's no object left, fill the page in the top
  694                          * object with zeros.
  695                          */
  696                         if (fs.object != fs.first_object) {
  697                                 vm_object_pip_wakeup(fs.object);
  698                                 VM_OBJECT_UNLOCK(fs.object);
  699 
  700                                 fs.object = fs.first_object;
  701                                 fs.pindex = fs.first_pindex;
  702                                 fs.m = fs.first_m;
  703                                 VM_OBJECT_LOCK(fs.object);
  704                         }
  705                         fs.first_m = NULL;
  706 
  707                         /*
  708                          * Zero the page if necessary and mark it valid.
  709                          */
  710                         if ((fs.m->flags & PG_ZERO) == 0) {
  711                                 pmap_zero_page(fs.m);
  712                         } else {
  713                                 PCPU_INC(cnt.v_ozfod);
  714                         }
  715                         PCPU_INC(cnt.v_zfod);
  716                         fs.m->valid = VM_PAGE_BITS_ALL;
  717                         break;  /* break to PAGE HAS BEEN FOUND */
  718                 } else {
  719                         KASSERT(fs.object != next_object,
  720                             ("object loop %p", next_object));
  721                         VM_OBJECT_LOCK(next_object);
  722                         vm_object_pip_add(next_object, 1);
  723                         if (fs.object != fs.first_object)
  724                                 vm_object_pip_wakeup(fs.object);
  725                         VM_OBJECT_UNLOCK(fs.object);
  726                         fs.object = next_object;
  727                 }
  728         }
  729 
  730         KASSERT((fs.m->oflags & VPO_BUSY) != 0,
  731             ("vm_fault: not busy after main loop"));
  732 
  733         /*
  734          * PAGE HAS BEEN FOUND. [Loop invariant still holds -- the object lock
  735          * is held.]
  736          */
  737 
  738         /*
  739          * If the page is being written, but isn't already owned by the
  740          * top-level object, we have to copy it into a new page owned by the
  741          * top-level object.
  742          */
  743         if (fs.object != fs.first_object) {
  744                 /*
  745                  * We only really need to copy if we want to write it.
  746                  */
  747                 if (fault_type & VM_PROT_WRITE) {
  748                         /*
  749                          * This allows pages to be virtually copied from a 
  750                          * backing_object into the first_object, where the 
  751                          * backing object has no other refs to it, and cannot
  752                          * gain any more refs.  Instead of a bcopy, we just 
  753                          * move the page from the backing object to the 
  754                          * first object.  Note that we must mark the page 
  755                          * dirty in the first object so that it will go out 
  756                          * to swap when needed.
  757                          */
  758                         is_first_object_locked = FALSE;
  759                         if (
  760                                 /*
  761                                  * Only one shadow object
  762                                  */
  763                                 (fs.object->shadow_count == 1) &&
  764                                 /*
  765                                  * No COW refs, except us
  766                                  */
  767                                 (fs.object->ref_count == 1) &&
  768                                 /*
  769                                  * No one else can look this object up
  770                                  */
  771                                 (fs.object->handle == NULL) &&
  772                                 /*
  773                                  * No other ways to look the object up
  774                                  */
  775                                 ((fs.object->type == OBJT_DEFAULT) ||
  776                                  (fs.object->type == OBJT_SWAP)) &&
  777                             (is_first_object_locked = VM_OBJECT_TRYLOCK(fs.first_object)) &&
  778                                 /*
  779                                  * We don't chase down the shadow chain
  780                                  */
  781                             fs.object == fs.first_object->backing_object) {
  782                                 vm_page_lock_queues();
  783                                 /*
  784                                  * get rid of the unnecessary page
  785                                  */
  786                                 vm_page_free(fs.first_m);
  787                                 /*
  788                                  * grab the page and put it into the 
  789                                  * process'es object.  The page is 
  790                                  * automatically made dirty.
  791                                  */
  792                                 vm_page_rename(fs.m, fs.first_object, fs.first_pindex);
  793                                 vm_page_unlock_queues();
  794                                 vm_page_busy(fs.m);
  795                                 fs.first_m = fs.m;
  796                                 fs.m = NULL;
  797                                 PCPU_INC(cnt.v_cow_optim);
  798                         } else {
  799                                 /*
  800                                  * Oh, well, lets copy it.
  801                                  */
  802                                 pmap_copy_page(fs.m, fs.first_m);
  803                                 fs.first_m->valid = VM_PAGE_BITS_ALL;
  804                         }
  805                         if (fs.m) {
  806                                 /*
  807                                  * We no longer need the old page or object.
  808                                  */
  809                                 release_page(&fs);
  810                         }
  811                         /*
  812                          * fs.object != fs.first_object due to above 
  813                          * conditional
  814                          */
  815                         vm_object_pip_wakeup(fs.object);
  816                         VM_OBJECT_UNLOCK(fs.object);
  817                         /*
  818                          * Only use the new page below...
  819                          */
  820                         fs.object = fs.first_object;
  821                         fs.pindex = fs.first_pindex;
  822                         fs.m = fs.first_m;
  823                         if (!is_first_object_locked)
  824                                 VM_OBJECT_LOCK(fs.object);
  825                         PCPU_INC(cnt.v_cow_faults);
  826                 } else {
  827                         prot &= ~VM_PROT_WRITE;
  828                 }
  829         }
  830 
  831         /*
  832          * We must verify that the maps have not changed since our last
  833          * lookup.
  834          */
  835         if (!fs.lookup_still_valid) {
  836                 vm_object_t retry_object;
  837                 vm_pindex_t retry_pindex;
  838                 vm_prot_t retry_prot;
  839 
  840                 if (!vm_map_trylock_read(fs.map)) {
  841                         release_page(&fs);
  842                         unlock_and_deallocate(&fs);
  843                         goto RetryFault;
  844                 }
  845                 fs.lookup_still_valid = TRUE;
  846                 if (fs.map->timestamp != map_generation) {
  847                         result = vm_map_lookup_locked(&fs.map, vaddr, fault_type,
  848                             &fs.entry, &retry_object, &retry_pindex, &retry_prot, &wired);
  849 
  850                         /*
  851                          * If we don't need the page any longer, put it on the inactive
  852                          * list (the easiest thing to do here).  If no one needs it,
  853                          * pageout will grab it eventually.
  854                          */
  855                         if (result != KERN_SUCCESS) {
  856                                 release_page(&fs);
  857                                 unlock_and_deallocate(&fs);
  858 
  859                                 /*
  860                                  * If retry of map lookup would have blocked then
  861                                  * retry fault from start.
  862                                  */
  863                                 if (result == KERN_FAILURE)
  864                                         goto RetryFault;
  865                                 return (result);
  866                         }
  867                         if ((retry_object != fs.first_object) ||
  868                             (retry_pindex != fs.first_pindex)) {
  869                                 release_page(&fs);
  870                                 unlock_and_deallocate(&fs);
  871                                 goto RetryFault;
  872                         }
  873 
  874                         /*
  875                          * Check whether the protection has changed or the object has
  876                          * been copied while we left the map unlocked. Changing from
  877                          * read to write permission is OK - we leave the page
  878                          * write-protected, and catch the write fault. Changing from
  879                          * write to read permission means that we can't mark the page
  880                          * write-enabled after all.
  881                          */
  882                         prot &= retry_prot;
  883                 }
  884         }
  885         /*
  886          * If the page was filled by a pager, update the map entry's
  887          * last read offset.  Since the pager does not return the
  888          * actual set of pages that it read, this update is based on
  889          * the requested set.  Typically, the requested and actual
  890          * sets are the same.
  891          *
  892          * XXX The following assignment modifies the map
  893          * without holding a write lock on it.
  894          */
  895         if (hardfault)
  896                 fs.entry->lastr = fs.pindex + faultcount - behind;
  897 
  898         if (prot & VM_PROT_WRITE) {
  899                 vm_object_set_writeable_dirty(fs.object);
  900 
  901                 /*
  902                  * If the fault is a write, we know that this page is being
  903                  * written NOW so dirty it explicitly to save on 
  904                  * pmap_is_modified() calls later.
  905                  *
  906                  * If this is a NOSYNC mmap we do not want to set VPO_NOSYNC
  907                  * if the page is already dirty to prevent data written with
  908                  * the expectation of being synced from not being synced.
  909                  * Likewise if this entry does not request NOSYNC then make
  910                  * sure the page isn't marked NOSYNC.  Applications sharing
  911                  * data should use the same flags to avoid ping ponging.
  912                  *
  913                  * Also tell the backing pager, if any, that it should remove
  914                  * any swap backing since the page is now dirty.
  915                  */
  916                 if (fs.entry->eflags & MAP_ENTRY_NOSYNC) {
  917                         if (fs.m->dirty == 0)
  918                                 fs.m->oflags |= VPO_NOSYNC;
  919                 } else {
  920                         fs.m->oflags &= ~VPO_NOSYNC;
  921                 }
  922                 if (fault_flags & VM_FAULT_DIRTY) {
  923                         vm_page_dirty(fs.m);
  924                         vm_pager_page_unswapped(fs.m);
  925                 }
  926         }
  927 
  928         /*
  929          * Page had better still be busy
  930          */
  931         KASSERT(fs.m->oflags & VPO_BUSY,
  932                 ("vm_fault: page %p not busy!", fs.m));
  933         /*
  934          * Page must be completely valid or it is not fit to
  935          * map into user space.  vm_pager_get_pages() ensures this.
  936          */
  937         KASSERT(fs.m->valid == VM_PAGE_BITS_ALL,
  938             ("vm_fault: page %p partially invalid", fs.m));
  939         VM_OBJECT_UNLOCK(fs.object);
  940 
  941         /*
  942          * Put this page into the physical map.  We had to do the unlock above
  943          * because pmap_enter() may sleep.  We don't put the page
  944          * back on the active queue until later so that the pageout daemon
  945          * won't find it (yet).
  946          */
  947         pmap_enter(fs.map->pmap, vaddr, fault_type, fs.m, prot, wired);
  948         if (((fault_flags & VM_FAULT_WIRE_MASK) == 0) && (wired == 0)) {
  949                 vm_fault_prefault(fs.map->pmap, vaddr, fs.entry);
  950         }
  951         VM_OBJECT_LOCK(fs.object);
  952         vm_page_lock_queues();
  953         vm_page_flag_set(fs.m, PG_REFERENCED);
  954 
  955         /*
  956          * If the page is not wired down, then put it where the pageout daemon
  957          * can find it.
  958          */
  959         if (fault_flags & VM_FAULT_WIRE_MASK) {
  960                 if (wired)
  961                         vm_page_wire(fs.m);
  962                 else
  963                         vm_page_unwire(fs.m, 1);
  964         } else {
  965                 vm_page_activate(fs.m);
  966         }
  967         vm_page_unlock_queues();
  968         vm_page_wakeup(fs.m);
  969 
  970         /*
  971          * Unlock everything, and return
  972          */
  973         unlock_and_deallocate(&fs);
  974         if (hardfault)
  975                 curthread->td_ru.ru_majflt++;
  976         else
  977                 curthread->td_ru.ru_minflt++;
  978 
  979         return (KERN_SUCCESS);
  980 }
  981 
  982 /*
  983  * vm_fault_prefault provides a quick way of clustering
  984  * pagefaults into a processes address space.  It is a "cousin"
  985  * of vm_map_pmap_enter, except it runs at page fault time instead
  986  * of mmap time.
  987  */
  988 static void
  989 vm_fault_prefault(pmap_t pmap, vm_offset_t addra, vm_map_entry_t entry)
  990 {
  991         int i;
  992         vm_offset_t addr, starta;
  993         vm_pindex_t pindex;
  994         vm_page_t m;
  995         vm_object_t object;
  996 
  997         if (pmap != vmspace_pmap(curthread->td_proc->p_vmspace))
  998                 return;
  999 
 1000         object = entry->object.vm_object;
 1001 
 1002         starta = addra - PFBAK * PAGE_SIZE;
 1003         if (starta < entry->start) {
 1004                 starta = entry->start;
 1005         } else if (starta > addra) {
 1006                 starta = 0;
 1007         }
 1008 
 1009         for (i = 0; i < PAGEORDER_SIZE; i++) {
 1010                 vm_object_t backing_object, lobject;
 1011 
 1012                 addr = addra + prefault_pageorder[i];
 1013                 if (addr > addra + (PFFOR * PAGE_SIZE))
 1014                         addr = 0;
 1015 
 1016                 if (addr < starta || addr >= entry->end)
 1017                         continue;
 1018 
 1019                 if (!pmap_is_prefaultable(pmap, addr))
 1020                         continue;
 1021 
 1022                 pindex = ((addr - entry->start) + entry->offset) >> PAGE_SHIFT;
 1023                 lobject = object;
 1024                 VM_OBJECT_LOCK(lobject);
 1025                 while ((m = vm_page_lookup(lobject, pindex)) == NULL &&
 1026                     lobject->type == OBJT_DEFAULT &&
 1027                     (backing_object = lobject->backing_object) != NULL) {
 1028                         KASSERT((lobject->backing_object_offset & PAGE_MASK) ==
 1029                             0, ("vm_fault_prefault: unaligned object offset"));
 1030                         pindex += lobject->backing_object_offset >> PAGE_SHIFT;
 1031                         VM_OBJECT_LOCK(backing_object);
 1032                         VM_OBJECT_UNLOCK(lobject);
 1033                         lobject = backing_object;
 1034                 }
 1035                 /*
 1036                  * give-up when a page is not in memory
 1037                  */
 1038                 if (m == NULL) {
 1039                         VM_OBJECT_UNLOCK(lobject);
 1040                         break;
 1041                 }
 1042                 if (m->valid == VM_PAGE_BITS_ALL &&
 1043                     (m->flags & PG_FICTITIOUS) == 0) {
 1044                         vm_page_lock_queues();
 1045                         pmap_enter_quick(pmap, addr, m, entry->protection);
 1046                         vm_page_unlock_queues();
 1047                 }
 1048                 VM_OBJECT_UNLOCK(lobject);
 1049         }
 1050 }
 1051 
 1052 /*
 1053  *      vm_fault_quick:
 1054  *
 1055  *      Ensure that the requested virtual address, which may be in userland,
 1056  *      is valid.  Fault-in the page if necessary.  Return -1 on failure.
 1057  */
 1058 int
 1059 vm_fault_quick(caddr_t v, int prot)
 1060 {
 1061         int r;
 1062 
 1063         if (prot & VM_PROT_WRITE)
 1064                 r = subyte(v, fubyte(v));
 1065         else
 1066                 r = fubyte(v);
 1067         return(r);
 1068 }
 1069 
 1070 /*
 1071  *      vm_fault_wire:
 1072  *
 1073  *      Wire down a range of virtual addresses in a map.
 1074  */
 1075 int
 1076 vm_fault_wire(vm_map_t map, vm_offset_t start, vm_offset_t end,
 1077     boolean_t user_wire, boolean_t fictitious)
 1078 {
 1079         vm_offset_t va;
 1080         int rv;
 1081 
 1082         /*
 1083          * We simulate a fault to get the page and enter it in the physical
 1084          * map.  For user wiring, we only ask for read access on currently
 1085          * read-only sections.
 1086          */
 1087         for (va = start; va < end; va += PAGE_SIZE) {
 1088                 rv = vm_fault(map, va,
 1089                     user_wire ? VM_PROT_READ : VM_PROT_READ | VM_PROT_WRITE,
 1090                     user_wire ? VM_FAULT_USER_WIRE : VM_FAULT_CHANGE_WIRING);
 1091                 if (rv) {
 1092                         if (va != start)
 1093                                 vm_fault_unwire(map, start, va, fictitious);
 1094                         return (rv);
 1095                 }
 1096         }
 1097         return (KERN_SUCCESS);
 1098 }
 1099 
 1100 /*
 1101  *      vm_fault_unwire:
 1102  *
 1103  *      Unwire a range of virtual addresses in a map.
 1104  */
 1105 void
 1106 vm_fault_unwire(vm_map_t map, vm_offset_t start, vm_offset_t end,
 1107     boolean_t fictitious)
 1108 {
 1109         vm_paddr_t pa;
 1110         vm_offset_t va;
 1111         pmap_t pmap;
 1112 
 1113         pmap = vm_map_pmap(map);
 1114 
 1115         /*
 1116          * Since the pages are wired down, we must be able to get their
 1117          * mappings from the physical map system.
 1118          */
 1119         for (va = start; va < end; va += PAGE_SIZE) {
 1120                 pa = pmap_extract(pmap, va);
 1121                 if (pa != 0) {
 1122                         pmap_change_wiring(pmap, va, FALSE);
 1123                         if (!fictitious) {
 1124                                 vm_page_lock_queues();
 1125                                 vm_page_unwire(PHYS_TO_VM_PAGE(pa), 1);
 1126                                 vm_page_unlock_queues();
 1127                         }
 1128                 }
 1129         }
 1130 }
 1131 
 1132 /*
 1133  *      Routine:
 1134  *              vm_fault_copy_entry
 1135  *      Function:
 1136  *              Create new shadow object backing dst_entry with private copy of
 1137  *              all underlying pages. When src_entry is equal to dst_entry,
 1138  *              function implements COW for wired-down map entry. Otherwise,
 1139  *              it forks wired entry into dst_map.
 1140  *
 1141  *      In/out conditions:
 1142  *              The source and destination maps must be locked for write.
 1143  *              The source map entry must be wired down (or be a sharing map
 1144  *              entry corresponding to a main map entry that is wired down).
 1145  */
 1146 void
 1147 vm_fault_copy_entry(vm_map_t dst_map, vm_map_t src_map,
 1148     vm_map_entry_t dst_entry, vm_map_entry_t src_entry,
 1149     vm_ooffset_t *fork_charge)
 1150 {
 1151         vm_object_t backing_object, dst_object, object, src_object;
 1152         vm_pindex_t dst_pindex, pindex, src_pindex;
 1153         vm_prot_t access, prot;
 1154         vm_offset_t vaddr;
 1155         vm_page_t dst_m;
 1156         vm_page_t src_m;
 1157         boolean_t src_readonly, upgrade;
 1158 
 1159 #ifdef  lint
 1160         src_map++;
 1161 #endif  /* lint */
 1162 
 1163         upgrade = src_entry == dst_entry;
 1164 
 1165         src_object = src_entry->object.vm_object;
 1166         src_pindex = OFF_TO_IDX(src_entry->offset);
 1167         src_readonly = (src_entry->protection & VM_PROT_WRITE) == 0;
 1168 
 1169         /*
 1170          * Create the top-level object for the destination entry. (Doesn't
 1171          * actually shadow anything - we copy the pages directly.)
 1172          */
 1173         dst_object = vm_object_allocate(OBJT_DEFAULT,
 1174             OFF_TO_IDX(dst_entry->end - dst_entry->start));
 1175 #if VM_NRESERVLEVEL > 0
 1176         dst_object->flags |= OBJ_COLORED;
 1177         dst_object->pg_color = atop(dst_entry->start);
 1178 #endif
 1179 
 1180         VM_OBJECT_LOCK(dst_object);
 1181         KASSERT(upgrade || dst_entry->object.vm_object == NULL,
 1182             ("vm_fault_copy_entry: vm_object not NULL"));
 1183         dst_entry->object.vm_object = dst_object;
 1184         dst_entry->offset = 0;
 1185         dst_object->charge = dst_entry->end - dst_entry->start;
 1186         if (fork_charge != NULL) {
 1187                 KASSERT(dst_entry->uip == NULL,
 1188                     ("vm_fault_copy_entry: leaked swp charge"));
 1189                 dst_object->uip = curthread->td_ucred->cr_ruidinfo;
 1190                 uihold(dst_object->uip);
 1191                 *fork_charge += dst_object->charge;
 1192         } else {
 1193                 dst_object->uip = dst_entry->uip;
 1194                 dst_entry->uip = NULL;
 1195         }
 1196         access = prot = dst_entry->max_protection;
 1197         /*
 1198          * If not an upgrade, then enter the mappings in the pmap as
 1199          * read and/or execute accesses.  Otherwise, enter them as
 1200          * write accesses.
 1201          *
 1202          * A writeable large page mapping is only created if all of
 1203          * the constituent small page mappings are modified. Marking
 1204          * PTEs as modified on inception allows promotion to happen
 1205          * without taking potentially large number of soft faults.
 1206          */
 1207         if (!upgrade)
 1208                 access &= ~VM_PROT_WRITE;
 1209 
 1210         /*
 1211          * Loop through all of the pages in the entry's range, copying each
 1212          * one from the source object (it should be there) to the destination
 1213          * object.
 1214          */
 1215         for (vaddr = dst_entry->start, dst_pindex = 0;
 1216             vaddr < dst_entry->end;
 1217             vaddr += PAGE_SIZE, dst_pindex++) {
 1218 
 1219                 /*
 1220                  * Allocate a page in the destination object.
 1221                  */
 1222                 do {
 1223                         dst_m = vm_page_alloc(dst_object, dst_pindex,
 1224                             VM_ALLOC_NORMAL);
 1225                         if (dst_m == NULL) {
 1226                                 VM_OBJECT_UNLOCK(dst_object);
 1227                                 VM_WAIT;
 1228                                 VM_OBJECT_LOCK(dst_object);
 1229                         }
 1230                 } while (dst_m == NULL);
 1231 
 1232                 /*
 1233                  * Find the page in the source object, and copy it in.
 1234                  * (Because the source is wired down, the page will be in
 1235                  * memory.)
 1236                  */
 1237                 VM_OBJECT_LOCK(src_object);
 1238                 object = src_object;
 1239                 pindex = src_pindex + dst_pindex;
 1240                 while ((src_m = vm_page_lookup(object, pindex)) == NULL &&
 1241                     src_readonly &&
 1242                     (backing_object = object->backing_object) != NULL) {
 1243                         /*
 1244                          * Allow fallback to backing objects if we are reading.
 1245                          */
 1246                         VM_OBJECT_LOCK(backing_object);
 1247                         pindex += OFF_TO_IDX(object->backing_object_offset);
 1248                         VM_OBJECT_UNLOCK(object);
 1249                         object = backing_object;
 1250                 }
 1251                 if (src_m == NULL)
 1252                         panic("vm_fault_copy_wired: page missing");
 1253                 pmap_copy_page(src_m, dst_m);
 1254                 VM_OBJECT_UNLOCK(object);
 1255                 dst_m->valid = VM_PAGE_BITS_ALL;
 1256                 VM_OBJECT_UNLOCK(dst_object);
 1257 
 1258                 /*
 1259                  * Enter it in the pmap. If a wired, copy-on-write
 1260                  * mapping is being replaced by a write-enabled
 1261                  * mapping, then wire that new mapping.
 1262                  */
 1263                 pmap_enter(dst_map->pmap, vaddr, access, dst_m, prot, upgrade);
 1264 
 1265                 /*
 1266                  * Mark it no longer busy, and put it on the active list.
 1267                  */
 1268                 VM_OBJECT_LOCK(dst_object);
 1269                 vm_page_lock_queues();
 1270                 if (upgrade) {
 1271                         vm_page_unwire(src_m, 0);
 1272                         vm_page_wire(dst_m);
 1273                 } else
 1274                         vm_page_activate(dst_m);
 1275                 vm_page_unlock_queues();
 1276                 vm_page_wakeup(dst_m);
 1277         }
 1278         VM_OBJECT_UNLOCK(dst_object);
 1279         if (upgrade) {
 1280                 dst_entry->eflags &= ~(MAP_ENTRY_COW | MAP_ENTRY_NEEDS_COPY);
 1281                 vm_object_deallocate(src_object);
 1282         }
 1283 }
 1284 
 1285 
 1286 /*
 1287  * This routine checks around the requested page for other pages that
 1288  * might be able to be faulted in.  This routine brackets the viable
 1289  * pages for the pages to be paged in.
 1290  *
 1291  * Inputs:
 1292  *      m, rbehind, rahead
 1293  *
 1294  * Outputs:
 1295  *  marray (array of vm_page_t), reqpage (index of requested page)
 1296  *
 1297  * Return value:
 1298  *  number of pages in marray
 1299  */
 1300 static int
 1301 vm_fault_additional_pages(m, rbehind, rahead, marray, reqpage)
 1302         vm_page_t m;
 1303         int rbehind;
 1304         int rahead;
 1305         vm_page_t *marray;
 1306         int *reqpage;
 1307 {
 1308         int i,j;
 1309         vm_object_t object;
 1310         vm_pindex_t pindex, startpindex, endpindex, tpindex;
 1311         vm_page_t rtm;
 1312         int cbehind, cahead;
 1313 
 1314         VM_OBJECT_LOCK_ASSERT(m->object, MA_OWNED);
 1315 
 1316         object = m->object;
 1317         pindex = m->pindex;
 1318         cbehind = cahead = 0;
 1319 
 1320         /*
 1321          * if the requested page is not available, then give up now
 1322          */
 1323         if (!vm_pager_has_page(object, pindex, &cbehind, &cahead)) {
 1324                 return 0;
 1325         }
 1326 
 1327         if ((cbehind == 0) && (cahead == 0)) {
 1328                 *reqpage = 0;
 1329                 marray[0] = m;
 1330                 return 1;
 1331         }
 1332 
 1333         if (rahead > cahead) {
 1334                 rahead = cahead;
 1335         }
 1336 
 1337         if (rbehind > cbehind) {
 1338                 rbehind = cbehind;
 1339         }
 1340 
 1341         /*
 1342          * scan backward for the read behind pages -- in memory 
 1343          */
 1344         if (pindex > 0) {
 1345                 if (rbehind > pindex) {
 1346                         rbehind = pindex;
 1347                         startpindex = 0;
 1348                 } else {
 1349                         startpindex = pindex - rbehind;
 1350                 }
 1351 
 1352                 if ((rtm = TAILQ_PREV(m, pglist, listq)) != NULL &&
 1353                     rtm->pindex >= startpindex)
 1354                         startpindex = rtm->pindex + 1;
 1355 
 1356                 /* tpindex is unsigned; beware of numeric underflow. */
 1357                 for (i = 0, tpindex = pindex - 1; tpindex >= startpindex &&
 1358                     tpindex < pindex; i++, tpindex--) {
 1359 
 1360                         rtm = vm_page_alloc(object, tpindex, VM_ALLOC_NORMAL |
 1361                             VM_ALLOC_IFNOTCACHED);
 1362                         if (rtm == NULL) {
 1363                                 /*
 1364                                  * Shift the allocated pages to the
 1365                                  * beginning of the array.
 1366                                  */
 1367                                 for (j = 0; j < i; j++) {
 1368                                         marray[j] = marray[j + tpindex + 1 -
 1369                                             startpindex];
 1370                                 }
 1371                                 break;
 1372                         }
 1373 
 1374                         marray[tpindex - startpindex] = rtm;
 1375                 }
 1376         } else {
 1377                 startpindex = 0;
 1378                 i = 0;
 1379         }
 1380 
 1381         marray[i] = m;
 1382         /* page offset of the required page */
 1383         *reqpage = i;
 1384 
 1385         tpindex = pindex + 1;
 1386         i++;
 1387 
 1388         /*
 1389          * scan forward for the read ahead pages
 1390          */
 1391         endpindex = tpindex + rahead;
 1392         if ((rtm = TAILQ_NEXT(m, listq)) != NULL && rtm->pindex < endpindex)
 1393                 endpindex = rtm->pindex;
 1394         if (endpindex > object->size)
 1395                 endpindex = object->size;
 1396 
 1397         for (; tpindex < endpindex; i++, tpindex++) {
 1398 
 1399                 rtm = vm_page_alloc(object, tpindex, VM_ALLOC_NORMAL |
 1400                     VM_ALLOC_IFNOTCACHED);
 1401                 if (rtm == NULL) {
 1402                         break;
 1403                 }
 1404 
 1405                 marray[i] = rtm;
 1406         }
 1407 
 1408         /* return number of pages */
 1409         return i;
 1410 }

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