xref: /freebsd/sys/vm/vm_fault.c (revision e40139ff33b48b56a24c808b166b04b8ee6f5b21)
1 /*-
2  * SPDX-License-Identifier: (BSD-4-Clause AND MIT-CMU)
3  *
4  * Copyright (c) 1991, 1993
5  *	The Regents of the University of California.  All rights reserved.
6  * Copyright (c) 1994 John S. Dyson
7  * All rights reserved.
8  * Copyright (c) 1994 David Greenman
9  * All rights reserved.
10  *
11  *
12  * This code is derived from software contributed to Berkeley by
13  * The Mach Operating System project at Carnegie-Mellon University.
14  *
15  * Redistribution and use in source and binary forms, with or without
16  * modification, are permitted provided that the following conditions
17  * are met:
18  * 1. Redistributions of source code must retain the above copyright
19  *    notice, this list of conditions and the following disclaimer.
20  * 2. Redistributions in binary form must reproduce the above copyright
21  *    notice, this list of conditions and the following disclaimer in the
22  *    documentation and/or other materials provided with the distribution.
23  * 3. All advertising materials mentioning features or use of this software
24  *    must display the following acknowledgement:
25  *	This product includes software developed by the University of
26  *	California, Berkeley and its contributors.
27  * 4. Neither the name of the University nor the names of its contributors
28  *    may be used to endorse or promote products derived from this software
29  *    without specific prior written permission.
30  *
31  * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
32  * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
33  * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
34  * ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
35  * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
36  * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
37  * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
38  * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
39  * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
40  * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
41  * SUCH DAMAGE.
42  *
43  *	from: @(#)vm_fault.c	8.4 (Berkeley) 1/12/94
44  *
45  *
46  * Copyright (c) 1987, 1990 Carnegie-Mellon University.
47  * All rights reserved.
48  *
49  * Authors: Avadis Tevanian, Jr., Michael Wayne Young
50  *
51  * Permission to use, copy, modify and distribute this software and
52  * its documentation is hereby granted, provided that both the copyright
53  * notice and this permission notice appear in all copies of the
54  * software, derivative works or modified versions, and any portions
55  * thereof, and that both notices appear in supporting documentation.
56  *
57  * CARNEGIE MELLON ALLOWS FREE USE OF THIS SOFTWARE IN ITS "AS IS"
58  * CONDITION.  CARNEGIE MELLON DISCLAIMS ANY LIABILITY OF ANY KIND
59  * FOR ANY DAMAGES WHATSOEVER RESULTING FROM THE USE OF THIS SOFTWARE.
60  *
61  * Carnegie Mellon requests users of this software to return to
62  *
63  *  Software Distribution Coordinator  or  Software.Distribution@CS.CMU.EDU
64  *  School of Computer Science
65  *  Carnegie Mellon University
66  *  Pittsburgh PA 15213-3890
67  *
68  * any improvements or extensions that they make and grant Carnegie the
69  * rights to redistribute these changes.
70  */
71 
72 /*
73  *	Page fault handling module.
74  */
75 
76 #include <sys/cdefs.h>
77 __FBSDID("$FreeBSD$");
78 
79 #include "opt_ktrace.h"
80 #include "opt_vm.h"
81 
82 #include <sys/param.h>
83 #include <sys/systm.h>
84 #include <sys/kernel.h>
85 #include <sys/lock.h>
86 #include <sys/mman.h>
87 #include <sys/mutex.h>
88 #include <sys/proc.h>
89 #include <sys/racct.h>
90 #include <sys/refcount.h>
91 #include <sys/resourcevar.h>
92 #include <sys/rwlock.h>
93 #include <sys/signalvar.h>
94 #include <sys/sysctl.h>
95 #include <sys/sysent.h>
96 #include <sys/vmmeter.h>
97 #include <sys/vnode.h>
98 #ifdef KTRACE
99 #include <sys/ktrace.h>
100 #endif
101 
102 #include <vm/vm.h>
103 #include <vm/vm_param.h>
104 #include <vm/pmap.h>
105 #include <vm/vm_map.h>
106 #include <vm/vm_object.h>
107 #include <vm/vm_page.h>
108 #include <vm/vm_pageout.h>
109 #include <vm/vm_kern.h>
110 #include <vm/vm_pager.h>
111 #include <vm/vm_extern.h>
112 #include <vm/vm_reserv.h>
113 
114 #define PFBAK 4
115 #define PFFOR 4
116 
117 #define	VM_FAULT_READ_DEFAULT	(1 + VM_FAULT_READ_AHEAD_INIT)
118 #define	VM_FAULT_READ_MAX	(1 + VM_FAULT_READ_AHEAD_MAX)
119 
120 #define	VM_FAULT_DONTNEED_MIN	1048576
121 
122 struct faultstate {
123 	vm_page_t m;
124 	vm_page_t m_cow;
125 	vm_object_t object;
126 	vm_pindex_t pindex;
127 	vm_page_t first_m;
128 	vm_object_t	first_object;
129 	vm_pindex_t first_pindex;
130 	vm_map_t map;
131 	vm_map_entry_t entry;
132 	int map_generation;
133 	bool lookup_still_valid;
134 	struct vnode *vp;
135 };
136 
137 static void vm_fault_dontneed(const struct faultstate *fs, vm_offset_t vaddr,
138 	    int ahead);
139 static void vm_fault_prefault(const struct faultstate *fs, vm_offset_t addra,
140 	    int backward, int forward, bool obj_locked);
141 
142 static int vm_pfault_oom_attempts = 3;
143 SYSCTL_INT(_vm, OID_AUTO, pfault_oom_attempts, CTLFLAG_RWTUN,
144     &vm_pfault_oom_attempts, 0,
145     "Number of page allocation attempts in page fault handler before it "
146     "triggers OOM handling");
147 
148 static int vm_pfault_oom_wait = 10;
149 SYSCTL_INT(_vm, OID_AUTO, pfault_oom_wait, CTLFLAG_RWTUN,
150     &vm_pfault_oom_wait, 0,
151     "Number of seconds to wait for free pages before retrying "
152     "the page fault handler");
153 
154 static inline void
155 fault_page_release(vm_page_t *mp)
156 {
157 	vm_page_t m;
158 
159 	m = *mp;
160 	if (m != NULL) {
161 		/*
162 		 * We are likely to loop around again and attempt to busy
163 		 * this page.  Deactivating it leaves it available for
164 		 * pageout while optimizing fault restarts.
165 		 */
166 		vm_page_deactivate(m);
167 		vm_page_xunbusy(m);
168 		*mp = NULL;
169 	}
170 }
171 
172 static inline void
173 fault_page_free(vm_page_t *mp)
174 {
175 	vm_page_t m;
176 
177 	m = *mp;
178 	if (m != NULL) {
179 		VM_OBJECT_ASSERT_WLOCKED(m->object);
180 		if (!vm_page_wired(m))
181 			vm_page_free(m);
182 		else
183 			vm_page_xunbusy(m);
184 		*mp = NULL;
185 	}
186 }
187 
188 static inline void
189 unlock_map(struct faultstate *fs)
190 {
191 
192 	if (fs->lookup_still_valid) {
193 		vm_map_lookup_done(fs->map, fs->entry);
194 		fs->lookup_still_valid = false;
195 	}
196 }
197 
198 static void
199 unlock_vp(struct faultstate *fs)
200 {
201 
202 	if (fs->vp != NULL) {
203 		vput(fs->vp);
204 		fs->vp = NULL;
205 	}
206 }
207 
208 static void
209 fault_deallocate(struct faultstate *fs)
210 {
211 
212 	fault_page_release(&fs->m_cow);
213 	fault_page_release(&fs->m);
214 	vm_object_pip_wakeup(fs->object);
215 	if (fs->object != fs->first_object) {
216 		VM_OBJECT_WLOCK(fs->first_object);
217 		fault_page_free(&fs->first_m);
218 		VM_OBJECT_WUNLOCK(fs->first_object);
219 		vm_object_pip_wakeup(fs->first_object);
220 	}
221 	vm_object_deallocate(fs->first_object);
222 	unlock_map(fs);
223 	unlock_vp(fs);
224 }
225 
226 static void
227 unlock_and_deallocate(struct faultstate *fs)
228 {
229 
230 	VM_OBJECT_WUNLOCK(fs->object);
231 	fault_deallocate(fs);
232 }
233 
234 static void
235 vm_fault_dirty(vm_map_entry_t entry, vm_page_t m, vm_prot_t prot,
236     vm_prot_t fault_type, int fault_flags)
237 {
238 	bool need_dirty;
239 
240 	if (((prot & VM_PROT_WRITE) == 0 &&
241 	    (fault_flags & VM_FAULT_DIRTY) == 0) ||
242 	    (m->oflags & VPO_UNMANAGED) != 0)
243 		return;
244 
245 	VM_PAGE_OBJECT_BUSY_ASSERT(m);
246 
247 	need_dirty = ((fault_type & VM_PROT_WRITE) != 0 &&
248 	    (fault_flags & VM_FAULT_WIRE) == 0) ||
249 	    (fault_flags & VM_FAULT_DIRTY) != 0;
250 
251 	vm_object_set_writeable_dirty(m->object);
252 
253 	/*
254 	 * If the fault is a write, we know that this page is being
255 	 * written NOW so dirty it explicitly to save on
256 	 * pmap_is_modified() calls later.
257 	 *
258 	 * Also, since the page is now dirty, we can possibly tell
259 	 * the pager to release any swap backing the page.
260 	 */
261 	if (need_dirty && vm_page_set_dirty(m) == 0) {
262 		/*
263 		 * If this is a NOSYNC mmap we do not want to set PGA_NOSYNC
264 		 * if the page is already dirty to prevent data written with
265 		 * the expectation of being synced from not being synced.
266 		 * Likewise if this entry does not request NOSYNC then make
267 		 * sure the page isn't marked NOSYNC.  Applications sharing
268 		 * data should use the same flags to avoid ping ponging.
269 		 */
270 		if ((entry->eflags & MAP_ENTRY_NOSYNC) != 0)
271 			vm_page_aflag_set(m, PGA_NOSYNC);
272 		else
273 			vm_page_aflag_clear(m, PGA_NOSYNC);
274 	}
275 
276 }
277 
278 /*
279  * Unlocks fs.first_object and fs.map on success.
280  */
281 static int
282 vm_fault_soft_fast(struct faultstate *fs, vm_offset_t vaddr, vm_prot_t prot,
283     int fault_type, int fault_flags, boolean_t wired, vm_page_t *m_hold)
284 {
285 	vm_page_t m, m_map;
286 #if (defined(__aarch64__) || defined(__amd64__) || (defined(__arm__) && \
287     __ARM_ARCH >= 6) || defined(__i386__) || defined(__riscv)) && \
288     VM_NRESERVLEVEL > 0
289 	vm_page_t m_super;
290 	int flags;
291 #endif
292 	int psind, rv;
293 
294 	MPASS(fs->vp == NULL);
295 	vm_object_busy(fs->first_object);
296 	m = vm_page_lookup(fs->first_object, fs->first_pindex);
297 	/* A busy page can be mapped for read|execute access. */
298 	if (m == NULL || ((prot & VM_PROT_WRITE) != 0 &&
299 	    vm_page_busied(m)) || !vm_page_all_valid(m)) {
300 		rv = KERN_FAILURE;
301 		goto out;
302 	}
303 	m_map = m;
304 	psind = 0;
305 #if (defined(__aarch64__) || defined(__amd64__) || (defined(__arm__) && \
306     __ARM_ARCH >= 6) || defined(__i386__) || defined(__riscv)) && \
307     VM_NRESERVLEVEL > 0
308 	if ((m->flags & PG_FICTITIOUS) == 0 &&
309 	    (m_super = vm_reserv_to_superpage(m)) != NULL &&
310 	    rounddown2(vaddr, pagesizes[m_super->psind]) >= fs->entry->start &&
311 	    roundup2(vaddr + 1, pagesizes[m_super->psind]) <= fs->entry->end &&
312 	    (vaddr & (pagesizes[m_super->psind] - 1)) == (VM_PAGE_TO_PHYS(m) &
313 	    (pagesizes[m_super->psind] - 1)) && !wired &&
314 	    pmap_ps_enabled(fs->map->pmap)) {
315 		flags = PS_ALL_VALID;
316 		if ((prot & VM_PROT_WRITE) != 0) {
317 			/*
318 			 * Create a superpage mapping allowing write access
319 			 * only if none of the constituent pages are busy and
320 			 * all of them are already dirty (except possibly for
321 			 * the page that was faulted on).
322 			 */
323 			flags |= PS_NONE_BUSY;
324 			if ((fs->first_object->flags & OBJ_UNMANAGED) == 0)
325 				flags |= PS_ALL_DIRTY;
326 		}
327 		if (vm_page_ps_test(m_super, flags, m)) {
328 			m_map = m_super;
329 			psind = m_super->psind;
330 			vaddr = rounddown2(vaddr, pagesizes[psind]);
331 			/* Preset the modified bit for dirty superpages. */
332 			if ((flags & PS_ALL_DIRTY) != 0)
333 				fault_type |= VM_PROT_WRITE;
334 		}
335 	}
336 #endif
337 	rv = pmap_enter(fs->map->pmap, vaddr, m_map, prot, fault_type |
338 	    PMAP_ENTER_NOSLEEP | (wired ? PMAP_ENTER_WIRED : 0), psind);
339 	if (rv != KERN_SUCCESS)
340 		goto out;
341 	if (m_hold != NULL) {
342 		*m_hold = m;
343 		vm_page_wire(m);
344 	}
345 	vm_fault_dirty(fs->entry, m, prot, fault_type, fault_flags);
346 	if (psind == 0 && !wired)
347 		vm_fault_prefault(fs, vaddr, PFBAK, PFFOR, true);
348 	VM_OBJECT_RUNLOCK(fs->first_object);
349 	vm_map_lookup_done(fs->map, fs->entry);
350 	curthread->td_ru.ru_minflt++;
351 
352 out:
353 	vm_object_unbusy(fs->first_object);
354 	return (rv);
355 }
356 
357 static void
358 vm_fault_restore_map_lock(struct faultstate *fs)
359 {
360 
361 	VM_OBJECT_ASSERT_WLOCKED(fs->first_object);
362 	MPASS(REFCOUNT_COUNT(fs->first_object->paging_in_progress) > 0);
363 
364 	if (!vm_map_trylock_read(fs->map)) {
365 		VM_OBJECT_WUNLOCK(fs->first_object);
366 		vm_map_lock_read(fs->map);
367 		VM_OBJECT_WLOCK(fs->first_object);
368 	}
369 	fs->lookup_still_valid = true;
370 }
371 
372 static void
373 vm_fault_populate_check_page(vm_page_t m)
374 {
375 
376 	/*
377 	 * Check each page to ensure that the pager is obeying the
378 	 * interface: the page must be installed in the object, fully
379 	 * valid, and exclusively busied.
380 	 */
381 	MPASS(m != NULL);
382 	MPASS(vm_page_all_valid(m));
383 	MPASS(vm_page_xbusied(m));
384 }
385 
386 static void
387 vm_fault_populate_cleanup(vm_object_t object, vm_pindex_t first,
388     vm_pindex_t last)
389 {
390 	vm_page_t m;
391 	vm_pindex_t pidx;
392 
393 	VM_OBJECT_ASSERT_WLOCKED(object);
394 	MPASS(first <= last);
395 	for (pidx = first, m = vm_page_lookup(object, pidx);
396 	    pidx <= last; pidx++, m = vm_page_next(m)) {
397 		vm_fault_populate_check_page(m);
398 		vm_page_deactivate(m);
399 		vm_page_xunbusy(m);
400 	}
401 }
402 
403 static int
404 vm_fault_populate(struct faultstate *fs, vm_prot_t prot, int fault_type,
405     int fault_flags, boolean_t wired, vm_page_t *m_hold)
406 {
407 	vm_offset_t vaddr;
408 	vm_page_t m;
409 	vm_pindex_t map_first, map_last, pager_first, pager_last, pidx;
410 	int i, npages, psind, rv;
411 
412 	MPASS(fs->object == fs->first_object);
413 	VM_OBJECT_ASSERT_WLOCKED(fs->first_object);
414 	MPASS(REFCOUNT_COUNT(fs->first_object->paging_in_progress) > 0);
415 	MPASS(fs->first_object->backing_object == NULL);
416 	MPASS(fs->lookup_still_valid);
417 
418 	pager_first = OFF_TO_IDX(fs->entry->offset);
419 	pager_last = pager_first + atop(fs->entry->end - fs->entry->start) - 1;
420 	unlock_map(fs);
421 	unlock_vp(fs);
422 
423 	/*
424 	 * Call the pager (driver) populate() method.
425 	 *
426 	 * There is no guarantee that the method will be called again
427 	 * if the current fault is for read, and a future fault is
428 	 * for write.  Report the entry's maximum allowed protection
429 	 * to the driver.
430 	 */
431 	rv = vm_pager_populate(fs->first_object, fs->first_pindex,
432 	    fault_type, fs->entry->max_protection, &pager_first, &pager_last);
433 
434 	VM_OBJECT_ASSERT_WLOCKED(fs->first_object);
435 	if (rv == VM_PAGER_BAD) {
436 		/*
437 		 * VM_PAGER_BAD is the backdoor for a pager to request
438 		 * normal fault handling.
439 		 */
440 		vm_fault_restore_map_lock(fs);
441 		if (fs->map->timestamp != fs->map_generation)
442 			return (KERN_RESOURCE_SHORTAGE); /* RetryFault */
443 		return (KERN_NOT_RECEIVER);
444 	}
445 	if (rv != VM_PAGER_OK)
446 		return (KERN_FAILURE); /* AKA SIGSEGV */
447 
448 	/* Ensure that the driver is obeying the interface. */
449 	MPASS(pager_first <= pager_last);
450 	MPASS(fs->first_pindex <= pager_last);
451 	MPASS(fs->first_pindex >= pager_first);
452 	MPASS(pager_last < fs->first_object->size);
453 
454 	vm_fault_restore_map_lock(fs);
455 	if (fs->map->timestamp != fs->map_generation) {
456 		vm_fault_populate_cleanup(fs->first_object, pager_first,
457 		    pager_last);
458 		return (KERN_RESOURCE_SHORTAGE); /* RetryFault */
459 	}
460 
461 	/*
462 	 * The map is unchanged after our last unlock.  Process the fault.
463 	 *
464 	 * The range [pager_first, pager_last] that is given to the
465 	 * pager is only a hint.  The pager may populate any range
466 	 * within the object that includes the requested page index.
467 	 * In case the pager expanded the range, clip it to fit into
468 	 * the map entry.
469 	 */
470 	map_first = OFF_TO_IDX(fs->entry->offset);
471 	if (map_first > pager_first) {
472 		vm_fault_populate_cleanup(fs->first_object, pager_first,
473 		    map_first - 1);
474 		pager_first = map_first;
475 	}
476 	map_last = map_first + atop(fs->entry->end - fs->entry->start) - 1;
477 	if (map_last < pager_last) {
478 		vm_fault_populate_cleanup(fs->first_object, map_last + 1,
479 		    pager_last);
480 		pager_last = map_last;
481 	}
482 	for (pidx = pager_first, m = vm_page_lookup(fs->first_object, pidx);
483 	    pidx <= pager_last;
484 	    pidx += npages, m = vm_page_next(&m[npages - 1])) {
485 		vaddr = fs->entry->start + IDX_TO_OFF(pidx) - fs->entry->offset;
486 #if defined(__aarch64__) || defined(__amd64__) || (defined(__arm__) && \
487     __ARM_ARCH >= 6) || defined(__i386__) || defined(__riscv)
488 		psind = m->psind;
489 		if (psind > 0 && ((vaddr & (pagesizes[psind] - 1)) != 0 ||
490 		    pidx + OFF_TO_IDX(pagesizes[psind]) - 1 > pager_last ||
491 		    !pmap_ps_enabled(fs->map->pmap) || wired))
492 			psind = 0;
493 #else
494 		psind = 0;
495 #endif
496 		npages = atop(pagesizes[psind]);
497 		for (i = 0; i < npages; i++) {
498 			vm_fault_populate_check_page(&m[i]);
499 			vm_fault_dirty(fs->entry, &m[i], prot, fault_type,
500 			    fault_flags);
501 		}
502 		VM_OBJECT_WUNLOCK(fs->first_object);
503 		rv = pmap_enter(fs->map->pmap, vaddr, m, prot, fault_type |
504 		    (wired ? PMAP_ENTER_WIRED : 0), psind);
505 #if defined(__amd64__)
506 		if (psind > 0 && rv == KERN_FAILURE) {
507 			for (i = 0; i < npages; i++) {
508 				rv = pmap_enter(fs->map->pmap, vaddr + ptoa(i),
509 				    &m[i], prot, fault_type |
510 				    (wired ? PMAP_ENTER_WIRED : 0), 0);
511 				MPASS(rv == KERN_SUCCESS);
512 			}
513 		}
514 #else
515 		MPASS(rv == KERN_SUCCESS);
516 #endif
517 		VM_OBJECT_WLOCK(fs->first_object);
518 		for (i = 0; i < npages; i++) {
519 			if ((fault_flags & VM_FAULT_WIRE) != 0)
520 				vm_page_wire(&m[i]);
521 			else
522 				vm_page_activate(&m[i]);
523 			if (m_hold != NULL && m[i].pindex == fs->first_pindex) {
524 				*m_hold = &m[i];
525 				vm_page_wire(&m[i]);
526 			}
527 			vm_page_xunbusy(&m[i]);
528 		}
529 	}
530 	curthread->td_ru.ru_majflt++;
531 	return (KERN_SUCCESS);
532 }
533 
534 static int prot_fault_translation;
535 SYSCTL_INT(_machdep, OID_AUTO, prot_fault_translation, CTLFLAG_RWTUN,
536     &prot_fault_translation, 0,
537     "Control signal to deliver on protection fault");
538 
539 /* compat definition to keep common code for signal translation */
540 #define	UCODE_PAGEFLT	12
541 #ifdef T_PAGEFLT
542 _Static_assert(UCODE_PAGEFLT == T_PAGEFLT, "T_PAGEFLT");
543 #endif
544 
545 /*
546  *	vm_fault_trap:
547  *
548  *	Handle a page fault occurring at the given address,
549  *	requiring the given permissions, in the map specified.
550  *	If successful, the page is inserted into the
551  *	associated physical map.
552  *
553  *	NOTE: the given address should be truncated to the
554  *	proper page address.
555  *
556  *	KERN_SUCCESS is returned if the page fault is handled; otherwise,
557  *	a standard error specifying why the fault is fatal is returned.
558  *
559  *	The map in question must be referenced, and remains so.
560  *	Caller may hold no locks.
561  */
562 int
563 vm_fault_trap(vm_map_t map, vm_offset_t vaddr, vm_prot_t fault_type,
564     int fault_flags, int *signo, int *ucode)
565 {
566 	int result;
567 
568 	MPASS(signo == NULL || ucode != NULL);
569 #ifdef KTRACE
570 	if (map != kernel_map && KTRPOINT(curthread, KTR_FAULT))
571 		ktrfault(vaddr, fault_type);
572 #endif
573 	result = vm_fault(map, trunc_page(vaddr), fault_type, fault_flags,
574 	    NULL);
575 	KASSERT(result == KERN_SUCCESS || result == KERN_FAILURE ||
576 	    result == KERN_INVALID_ADDRESS ||
577 	    result == KERN_RESOURCE_SHORTAGE ||
578 	    result == KERN_PROTECTION_FAILURE ||
579 	    result == KERN_OUT_OF_BOUNDS,
580 	    ("Unexpected Mach error %d from vm_fault()", result));
581 #ifdef KTRACE
582 	if (map != kernel_map && KTRPOINT(curthread, KTR_FAULTEND))
583 		ktrfaultend(result);
584 #endif
585 	if (result != KERN_SUCCESS && signo != NULL) {
586 		switch (result) {
587 		case KERN_FAILURE:
588 		case KERN_INVALID_ADDRESS:
589 			*signo = SIGSEGV;
590 			*ucode = SEGV_MAPERR;
591 			break;
592 		case KERN_RESOURCE_SHORTAGE:
593 			*signo = SIGBUS;
594 			*ucode = BUS_OOMERR;
595 			break;
596 		case KERN_OUT_OF_BOUNDS:
597 			*signo = SIGBUS;
598 			*ucode = BUS_OBJERR;
599 			break;
600 		case KERN_PROTECTION_FAILURE:
601 			if (prot_fault_translation == 0) {
602 				/*
603 				 * Autodetect.  This check also covers
604 				 * the images without the ABI-tag ELF
605 				 * note.
606 				 */
607 				if (SV_CURPROC_ABI() == SV_ABI_FREEBSD &&
608 				    curproc->p_osrel >= P_OSREL_SIGSEGV) {
609 					*signo = SIGSEGV;
610 					*ucode = SEGV_ACCERR;
611 				} else {
612 					*signo = SIGBUS;
613 					*ucode = UCODE_PAGEFLT;
614 				}
615 			} else if (prot_fault_translation == 1) {
616 				/* Always compat mode. */
617 				*signo = SIGBUS;
618 				*ucode = UCODE_PAGEFLT;
619 			} else {
620 				/* Always SIGSEGV mode. */
621 				*signo = SIGSEGV;
622 				*ucode = SEGV_ACCERR;
623 			}
624 			break;
625 		default:
626 			KASSERT(0, ("Unexpected Mach error %d from vm_fault()",
627 			    result));
628 			break;
629 		}
630 	}
631 	return (result);
632 }
633 
634 static int
635 vm_fault_lock_vnode(struct faultstate *fs)
636 {
637 	struct vnode *vp;
638 	int error, locked;
639 
640 	if (fs->object->type != OBJT_VNODE)
641 		return (KERN_SUCCESS);
642 	vp = fs->object->handle;
643 	if (vp == fs->vp) {
644 		ASSERT_VOP_LOCKED(vp, "saved vnode is not locked");
645 		return (KERN_SUCCESS);
646 	}
647 
648 	/*
649 	 * Perform an unlock in case the desired vnode changed while
650 	 * the map was unlocked during a retry.
651 	 */
652 	unlock_vp(fs);
653 
654 	locked = VOP_ISLOCKED(vp);
655 	if (locked != LK_EXCLUSIVE)
656 		locked = LK_SHARED;
657 
658 	/*
659 	 * We must not sleep acquiring the vnode lock while we have
660 	 * the page exclusive busied or the object's
661 	 * paging-in-progress count incremented.  Otherwise, we could
662 	 * deadlock.
663 	 */
664 	error = vget(vp, locked | LK_CANRECURSE | LK_NOWAIT, curthread);
665 	if (error == 0) {
666 		fs->vp = vp;
667 		return (KERN_SUCCESS);
668 	}
669 
670 	vhold(vp);
671 	unlock_and_deallocate(fs);
672 	error = vget(vp, locked | LK_RETRY | LK_CANRECURSE, curthread);
673 	vdrop(vp);
674 	fs->vp = vp;
675 	KASSERT(error == 0, ("vm_fault: vget failed %d", error));
676 	return (KERN_RESOURCE_SHORTAGE);
677 }
678 
679 /*
680  * Wait/Retry if the page is busy.  We have to do this if the page is
681  * either exclusive or shared busy because the vm_pager may be using
682  * read busy for pageouts (and even pageins if it is the vnode pager),
683  * and we could end up trying to pagein and pageout the same page
684  * simultaneously.
685  *
686  * We can theoretically allow the busy case on a read fault if the page
687  * is marked valid, but since such pages are typically already pmap'd,
688  * putting that special case in might be more effort then it is worth.
689  * We cannot under any circumstances mess around with a shared busied
690  * page except, perhaps, to pmap it.
691  */
692 static void
693 vm_fault_busy_sleep(struct faultstate *fs)
694 {
695 	/*
696 	 * Reference the page before unlocking and
697 	 * sleeping so that the page daemon is less
698 	 * likely to reclaim it.
699 	 */
700 	vm_page_aflag_set(fs->m, PGA_REFERENCED);
701 	if (fs->object != fs->first_object) {
702 		fault_page_release(&fs->first_m);
703 		vm_object_pip_wakeup(fs->first_object);
704 	}
705 	vm_object_pip_wakeup(fs->object);
706 	unlock_map(fs);
707 	if (fs->m == vm_page_lookup(fs->object, fs->pindex))
708 		vm_page_busy_sleep(fs->m, "vmpfw", false);
709 	else
710 		VM_OBJECT_WUNLOCK(fs->object);
711 	VM_CNT_INC(v_intrans);
712 	vm_object_deallocate(fs->first_object);
713 }
714 
715 int
716 vm_fault(vm_map_t map, vm_offset_t vaddr, vm_prot_t fault_type,
717     int fault_flags, vm_page_t *m_hold)
718 {
719 	struct faultstate fs;
720 	struct domainset *dset;
721 	vm_object_t next_object, retry_object;
722 	vm_offset_t e_end, e_start;
723 	vm_pindex_t retry_pindex;
724 	vm_prot_t prot, retry_prot;
725 	int ahead, alloc_req, behind, cluster_offset, era, faultcount;
726 	int nera, oom, result, rv;
727 	u_char behavior;
728 	boolean_t wired;	/* Passed by reference. */
729 	bool dead, hardfault, is_first_object_locked;
730 
731 	VM_CNT_INC(v_vm_faults);
732 
733 	if ((curthread->td_pflags & TDP_NOFAULTING) != 0)
734 		return (KERN_PROTECTION_FAILURE);
735 
736 	fs.vp = NULL;
737 	faultcount = 0;
738 	nera = -1;
739 	hardfault = false;
740 
741 RetryFault:
742 	oom = 0;
743 RetryFault_oom:
744 
745 	/*
746 	 * Find the backing store object and offset into it to begin the
747 	 * search.
748 	 */
749 	fs.map = map;
750 	result = vm_map_lookup(&fs.map, vaddr, fault_type |
751 	    VM_PROT_FAULT_LOOKUP, &fs.entry, &fs.first_object,
752 	    &fs.first_pindex, &prot, &wired);
753 	if (result != KERN_SUCCESS) {
754 		unlock_vp(&fs);
755 		return (result);
756 	}
757 
758 	fs.map_generation = fs.map->timestamp;
759 
760 	if (fs.entry->eflags & MAP_ENTRY_NOFAULT) {
761 		panic("%s: fault on nofault entry, addr: %#lx",
762 		    __func__, (u_long)vaddr);
763 	}
764 
765 	if (fs.entry->eflags & MAP_ENTRY_IN_TRANSITION &&
766 	    fs.entry->wiring_thread != curthread) {
767 		vm_map_unlock_read(fs.map);
768 		vm_map_lock(fs.map);
769 		if (vm_map_lookup_entry(fs.map, vaddr, &fs.entry) &&
770 		    (fs.entry->eflags & MAP_ENTRY_IN_TRANSITION)) {
771 			unlock_vp(&fs);
772 			fs.entry->eflags |= MAP_ENTRY_NEEDS_WAKEUP;
773 			vm_map_unlock_and_wait(fs.map, 0);
774 		} else
775 			vm_map_unlock(fs.map);
776 		goto RetryFault;
777 	}
778 
779 	MPASS((fs.entry->eflags & MAP_ENTRY_GUARD) == 0);
780 
781 	if (wired)
782 		fault_type = prot | (fault_type & VM_PROT_COPY);
783 	else
784 		KASSERT((fault_flags & VM_FAULT_WIRE) == 0,
785 		    ("!wired && VM_FAULT_WIRE"));
786 
787 	/*
788 	 * Try to avoid lock contention on the top-level object through
789 	 * special-case handling of some types of page faults, specifically,
790 	 * those that are mapping an existing page from the top-level object.
791 	 * Under this condition, a read lock on the object suffices, allowing
792 	 * multiple page faults of a similar type to run in parallel.
793 	 */
794 	if (fs.vp == NULL /* avoid locked vnode leak */ &&
795 	    (fault_flags & (VM_FAULT_WIRE | VM_FAULT_DIRTY)) == 0) {
796 		VM_OBJECT_RLOCK(fs.first_object);
797 		rv = vm_fault_soft_fast(&fs, vaddr, prot, fault_type,
798 		    fault_flags, wired, m_hold);
799 		if (rv == KERN_SUCCESS)
800 			return (rv);
801 		if (!VM_OBJECT_TRYUPGRADE(fs.first_object)) {
802 			VM_OBJECT_RUNLOCK(fs.first_object);
803 			VM_OBJECT_WLOCK(fs.first_object);
804 		}
805 	} else {
806 		VM_OBJECT_WLOCK(fs.first_object);
807 	}
808 
809 	/*
810 	 * Make a reference to this object to prevent its disposal while we
811 	 * are messing with it.  Once we have the reference, the map is free
812 	 * to be diddled.  Since objects reference their shadows (and copies),
813 	 * they will stay around as well.
814 	 *
815 	 * Bump the paging-in-progress count to prevent size changes (e.g.
816 	 * truncation operations) during I/O.
817 	 */
818 	vm_object_reference_locked(fs.first_object);
819 	vm_object_pip_add(fs.first_object, 1);
820 
821 	fs.lookup_still_valid = true;
822 
823 	fs.m_cow = fs.m = fs.first_m = NULL;
824 
825 	/*
826 	 * Search for the page at object/offset.
827 	 */
828 	fs.object = fs.first_object;
829 	fs.pindex = fs.first_pindex;
830 	while (TRUE) {
831 		KASSERT(fs.m == NULL,
832 		    ("page still set %p at loop start", fs.m));
833 		/*
834 		 * If the object is marked for imminent termination,
835 		 * we retry here, since the collapse pass has raced
836 		 * with us.  Otherwise, if we see terminally dead
837 		 * object, return fail.
838 		 */
839 		if ((fs.object->flags & OBJ_DEAD) != 0) {
840 			dead = fs.object->type == OBJT_DEAD;
841 			unlock_and_deallocate(&fs);
842 			if (dead)
843 				return (KERN_PROTECTION_FAILURE);
844 			pause("vmf_de", 1);
845 			goto RetryFault;
846 		}
847 
848 		/*
849 		 * See if page is resident
850 		 */
851 		fs.m = vm_page_lookup(fs.object, fs.pindex);
852 		if (fs.m != NULL) {
853 			if (vm_page_tryxbusy(fs.m) == 0) {
854 				vm_fault_busy_sleep(&fs);
855 				goto RetryFault;
856 			}
857 
858 			/*
859 			 * The page is marked busy for other processes and the
860 			 * pagedaemon.  If it still isn't completely valid
861 			 * (readable), jump to readrest, else break-out ( we
862 			 * found the page ).
863 			 */
864 			if (!vm_page_all_valid(fs.m))
865 				goto readrest;
866 			break; /* break to PAGE HAS BEEN FOUND */
867 		}
868 		KASSERT(fs.m == NULL, ("fs.m should be NULL, not %p", fs.m));
869 
870 		/*
871 		 * Page is not resident.  If the pager might contain the page
872 		 * or this is the beginning of the search, allocate a new
873 		 * page.  (Default objects are zero-fill, so there is no real
874 		 * pager for them.)
875 		 */
876 		if (fs.object->type != OBJT_DEFAULT ||
877 		    fs.object == fs.first_object) {
878 			if ((fs.object->flags & OBJ_SIZEVNLOCK) != 0) {
879 				rv = vm_fault_lock_vnode(&fs);
880 				MPASS(rv == KERN_SUCCESS ||
881 				    rv == KERN_RESOURCE_SHORTAGE);
882 				if (rv == KERN_RESOURCE_SHORTAGE)
883 					goto RetryFault;
884 			}
885 			if (fs.pindex >= fs.object->size) {
886 				unlock_and_deallocate(&fs);
887 				return (KERN_OUT_OF_BOUNDS);
888 			}
889 
890 			if (fs.object == fs.first_object &&
891 			    (fs.first_object->flags & OBJ_POPULATE) != 0 &&
892 			    fs.first_object->shadow_count == 0) {
893 				rv = vm_fault_populate(&fs, prot, fault_type,
894 				    fault_flags, wired, m_hold);
895 				switch (rv) {
896 				case KERN_SUCCESS:
897 				case KERN_FAILURE:
898 					unlock_and_deallocate(&fs);
899 					return (rv);
900 				case KERN_RESOURCE_SHORTAGE:
901 					unlock_and_deallocate(&fs);
902 					goto RetryFault;
903 				case KERN_NOT_RECEIVER:
904 					/*
905 					 * Pager's populate() method
906 					 * returned VM_PAGER_BAD.
907 					 */
908 					break;
909 				default:
910 					panic("inconsistent return codes");
911 				}
912 			}
913 
914 			/*
915 			 * Allocate a new page for this object/offset pair.
916 			 *
917 			 * Unlocked read of the p_flag is harmless. At
918 			 * worst, the P_KILLED might be not observed
919 			 * there, and allocation can fail, causing
920 			 * restart and new reading of the p_flag.
921 			 */
922 			dset = fs.object->domain.dr_policy;
923 			if (dset == NULL)
924 				dset = curthread->td_domain.dr_policy;
925 			if (!vm_page_count_severe_set(&dset->ds_mask) ||
926 			    P_KILLED(curproc)) {
927 #if VM_NRESERVLEVEL > 0
928 				vm_object_color(fs.object, atop(vaddr) -
929 				    fs.pindex);
930 #endif
931 				alloc_req = P_KILLED(curproc) ?
932 				    VM_ALLOC_SYSTEM : VM_ALLOC_NORMAL;
933 				if (fs.object->type != OBJT_VNODE &&
934 				    fs.object->backing_object == NULL)
935 					alloc_req |= VM_ALLOC_ZERO;
936 				fs.m = vm_page_alloc(fs.object, fs.pindex,
937 				    alloc_req);
938 			}
939 			if (fs.m == NULL) {
940 				unlock_and_deallocate(&fs);
941 				if (vm_pfault_oom_attempts < 0 ||
942 				    oom < vm_pfault_oom_attempts) {
943 					oom++;
944 					vm_waitpfault(dset,
945 					    vm_pfault_oom_wait * hz);
946 					goto RetryFault_oom;
947 				}
948 				if (bootverbose)
949 					printf(
950 	"proc %d (%s) failed to alloc page on fault, starting OOM\n",
951 					    curproc->p_pid, curproc->p_comm);
952 				vm_pageout_oom(VM_OOM_MEM_PF);
953 				goto RetryFault;
954 			}
955 		}
956 
957 readrest:
958 		/*
959 		 * At this point, we have either allocated a new page or found
960 		 * an existing page that is only partially valid.
961 		 *
962 		 * We hold a reference on the current object and the page is
963 		 * exclusive busied.
964 		 */
965 
966 		/*
967 		 * If the pager for the current object might have the page,
968 		 * then determine the number of additional pages to read and
969 		 * potentially reprioritize previously read pages for earlier
970 		 * reclamation.  These operations should only be performed
971 		 * once per page fault.  Even if the current pager doesn't
972 		 * have the page, the number of additional pages to read will
973 		 * apply to subsequent objects in the shadow chain.
974 		 */
975 		if (fs.object->type != OBJT_DEFAULT && nera == -1 &&
976 		    !P_KILLED(curproc)) {
977 			KASSERT(fs.lookup_still_valid, ("map unlocked"));
978 			era = fs.entry->read_ahead;
979 			behavior = vm_map_entry_behavior(fs.entry);
980 			if (behavior == MAP_ENTRY_BEHAV_RANDOM) {
981 				nera = 0;
982 			} else if (behavior == MAP_ENTRY_BEHAV_SEQUENTIAL) {
983 				nera = VM_FAULT_READ_AHEAD_MAX;
984 				if (vaddr == fs.entry->next_read)
985 					vm_fault_dontneed(&fs, vaddr, nera);
986 			} else if (vaddr == fs.entry->next_read) {
987 				/*
988 				 * This is a sequential fault.  Arithmetically
989 				 * increase the requested number of pages in
990 				 * the read-ahead window.  The requested
991 				 * number of pages is "# of sequential faults
992 				 * x (read ahead min + 1) + read ahead min"
993 				 */
994 				nera = VM_FAULT_READ_AHEAD_MIN;
995 				if (era > 0) {
996 					nera += era + 1;
997 					if (nera > VM_FAULT_READ_AHEAD_MAX)
998 						nera = VM_FAULT_READ_AHEAD_MAX;
999 				}
1000 				if (era == VM_FAULT_READ_AHEAD_MAX)
1001 					vm_fault_dontneed(&fs, vaddr, nera);
1002 			} else {
1003 				/*
1004 				 * This is a non-sequential fault.
1005 				 */
1006 				nera = 0;
1007 			}
1008 			if (era != nera) {
1009 				/*
1010 				 * A read lock on the map suffices to update
1011 				 * the read ahead count safely.
1012 				 */
1013 				fs.entry->read_ahead = nera;
1014 			}
1015 
1016 			/*
1017 			 * Prepare for unlocking the map.  Save the map
1018 			 * entry's start and end addresses, which are used to
1019 			 * optimize the size of the pager operation below.
1020 			 * Even if the map entry's addresses change after
1021 			 * unlocking the map, using the saved addresses is
1022 			 * safe.
1023 			 */
1024 			e_start = fs.entry->start;
1025 			e_end = fs.entry->end;
1026 		}
1027 
1028 		/*
1029 		 * Call the pager to retrieve the page if there is a chance
1030 		 * that the pager has it, and potentially retrieve additional
1031 		 * pages at the same time.
1032 		 */
1033 		if (fs.object->type != OBJT_DEFAULT) {
1034 			/*
1035 			 * Release the map lock before locking the vnode or
1036 			 * sleeping in the pager.  (If the current object has
1037 			 * a shadow, then an earlier iteration of this loop
1038 			 * may have already unlocked the map.)
1039 			 */
1040 			unlock_map(&fs);
1041 
1042 			rv = vm_fault_lock_vnode(&fs);
1043 			MPASS(rv == KERN_SUCCESS ||
1044 			    rv == KERN_RESOURCE_SHORTAGE);
1045 			if (rv == KERN_RESOURCE_SHORTAGE)
1046 				goto RetryFault;
1047 			KASSERT(fs.vp == NULL || !fs.map->system_map,
1048 			    ("vm_fault: vnode-backed object mapped by system map"));
1049 
1050 			/*
1051 			 * Page in the requested page and hint the pager,
1052 			 * that it may bring up surrounding pages.
1053 			 */
1054 			if (nera == -1 || behavior == MAP_ENTRY_BEHAV_RANDOM ||
1055 			    P_KILLED(curproc)) {
1056 				behind = 0;
1057 				ahead = 0;
1058 			} else {
1059 				/* Is this a sequential fault? */
1060 				if (nera > 0) {
1061 					behind = 0;
1062 					ahead = nera;
1063 				} else {
1064 					/*
1065 					 * Request a cluster of pages that is
1066 					 * aligned to a VM_FAULT_READ_DEFAULT
1067 					 * page offset boundary within the
1068 					 * object.  Alignment to a page offset
1069 					 * boundary is more likely to coincide
1070 					 * with the underlying file system
1071 					 * block than alignment to a virtual
1072 					 * address boundary.
1073 					 */
1074 					cluster_offset = fs.pindex %
1075 					    VM_FAULT_READ_DEFAULT;
1076 					behind = ulmin(cluster_offset,
1077 					    atop(vaddr - e_start));
1078 					ahead = VM_FAULT_READ_DEFAULT - 1 -
1079 					    cluster_offset;
1080 				}
1081 				ahead = ulmin(ahead, atop(e_end - vaddr) - 1);
1082 			}
1083 			VM_OBJECT_WUNLOCK(fs.object);
1084 			rv = vm_pager_get_pages(fs.object, &fs.m, 1,
1085 			    &behind, &ahead);
1086 			VM_OBJECT_WLOCK(fs.object);
1087 			if (rv == VM_PAGER_OK) {
1088 				faultcount = behind + 1 + ahead;
1089 				hardfault = true;
1090 				break; /* break to PAGE HAS BEEN FOUND */
1091 			}
1092 			if (rv == VM_PAGER_ERROR)
1093 				printf("vm_fault: pager read error, pid %d (%s)\n",
1094 				    curproc->p_pid, curproc->p_comm);
1095 
1096 			/*
1097 			 * If an I/O error occurred or the requested page was
1098 			 * outside the range of the pager, clean up and return
1099 			 * an error.
1100 			 */
1101 			if (rv == VM_PAGER_ERROR || rv == VM_PAGER_BAD) {
1102 				fault_page_free(&fs.m);
1103 				unlock_and_deallocate(&fs);
1104 				return (KERN_OUT_OF_BOUNDS);
1105 			}
1106 
1107 		}
1108 
1109 		/*
1110 		 * The requested page does not exist at this object/
1111 		 * offset.  Remove the invalid page from the object,
1112 		 * waking up anyone waiting for it, and continue on to
1113 		 * the next object.  However, if this is the top-level
1114 		 * object, we must leave the busy page in place to
1115 		 * prevent another process from rushing past us, and
1116 		 * inserting the page in that object at the same time
1117 		 * that we are.
1118 		 */
1119 		if (fs.object == fs.first_object) {
1120 			fs.first_m = fs.m;
1121 			fs.m = NULL;
1122 		} else
1123 			fault_page_free(&fs.m);
1124 
1125 		/*
1126 		 * Move on to the next object.  Lock the next object before
1127 		 * unlocking the current one.
1128 		 */
1129 		next_object = fs.object->backing_object;
1130 		if (next_object == NULL) {
1131 			/*
1132 			 * If there's no object left, fill the page in the top
1133 			 * object with zeros.
1134 			 */
1135 			if (fs.object != fs.first_object) {
1136 				vm_object_pip_wakeup(fs.object);
1137 				VM_OBJECT_WUNLOCK(fs.object);
1138 
1139 				fs.object = fs.first_object;
1140 				fs.pindex = fs.first_pindex;
1141 				VM_OBJECT_WLOCK(fs.object);
1142 			}
1143 			MPASS(fs.first_m != NULL);
1144 			MPASS(fs.m == NULL);
1145 			fs.m = fs.first_m;
1146 			fs.first_m = NULL;
1147 
1148 			/*
1149 			 * Zero the page if necessary and mark it valid.
1150 			 */
1151 			if ((fs.m->flags & PG_ZERO) == 0) {
1152 				pmap_zero_page(fs.m);
1153 			} else {
1154 				VM_CNT_INC(v_ozfod);
1155 			}
1156 			VM_CNT_INC(v_zfod);
1157 			vm_page_valid(fs.m);
1158 			/* Don't try to prefault neighboring pages. */
1159 			faultcount = 1;
1160 			break;	/* break to PAGE HAS BEEN FOUND */
1161 		} else {
1162 			MPASS(fs.first_m != NULL);
1163 			KASSERT(fs.object != next_object,
1164 			    ("object loop %p", next_object));
1165 			VM_OBJECT_WLOCK(next_object);
1166 			vm_object_pip_add(next_object, 1);
1167 			if (fs.object != fs.first_object)
1168 				vm_object_pip_wakeup(fs.object);
1169 			fs.pindex +=
1170 			    OFF_TO_IDX(fs.object->backing_object_offset);
1171 			VM_OBJECT_WUNLOCK(fs.object);
1172 			fs.object = next_object;
1173 		}
1174 	}
1175 
1176 	vm_page_assert_xbusied(fs.m);
1177 
1178 	/*
1179 	 * PAGE HAS BEEN FOUND. [Loop invariant still holds -- the object lock
1180 	 * is held.]
1181 	 */
1182 
1183 	/*
1184 	 * If the page is being written, but isn't already owned by the
1185 	 * top-level object, we have to copy it into a new page owned by the
1186 	 * top-level object.
1187 	 */
1188 	if (fs.object != fs.first_object) {
1189 		/*
1190 		 * We only really need to copy if we want to write it.
1191 		 */
1192 		if ((fault_type & (VM_PROT_COPY | VM_PROT_WRITE)) != 0) {
1193 			/*
1194 			 * This allows pages to be virtually copied from a
1195 			 * backing_object into the first_object, where the
1196 			 * backing object has no other refs to it, and cannot
1197 			 * gain any more refs.  Instead of a bcopy, we just
1198 			 * move the page from the backing object to the
1199 			 * first object.  Note that we must mark the page
1200 			 * dirty in the first object so that it will go out
1201 			 * to swap when needed.
1202 			 */
1203 			is_first_object_locked = false;
1204 			if (
1205 				/*
1206 				 * Only one shadow object
1207 				 */
1208 				(fs.object->shadow_count == 1) &&
1209 				/*
1210 				 * No COW refs, except us
1211 				 */
1212 				(fs.object->ref_count == 1) &&
1213 				/*
1214 				 * No one else can look this object up
1215 				 */
1216 				(fs.object->handle == NULL) &&
1217 				/*
1218 				 * No other ways to look the object up
1219 				 */
1220 				((fs.object->flags & OBJ_ANON) != 0) &&
1221 			    (is_first_object_locked = VM_OBJECT_TRYWLOCK(fs.first_object)) &&
1222 				/*
1223 				 * We don't chase down the shadow chain
1224 				 */
1225 			    fs.object == fs.first_object->backing_object) {
1226 
1227 				/*
1228 				 * Remove but keep xbusy for replace.  fs.m is
1229 				 * moved into fs.first_object and left busy
1230 				 * while fs.first_m is conditionally freed.
1231 				 */
1232 				vm_page_remove_xbusy(fs.m);
1233 				vm_page_replace(fs.m, fs.first_object,
1234 				    fs.first_pindex, fs.first_m);
1235 				vm_page_dirty(fs.m);
1236 #if VM_NRESERVLEVEL > 0
1237 				/*
1238 				 * Rename the reservation.
1239 				 */
1240 				vm_reserv_rename(fs.m, fs.first_object,
1241 				    fs.object, OFF_TO_IDX(
1242 				    fs.first_object->backing_object_offset));
1243 #endif
1244 				VM_OBJECT_WUNLOCK(fs.object);
1245 				fs.first_m = fs.m;
1246 				fs.m = NULL;
1247 				VM_CNT_INC(v_cow_optim);
1248 			} else {
1249 				VM_OBJECT_WUNLOCK(fs.object);
1250 				/*
1251 				 * Oh, well, lets copy it.
1252 				 */
1253 				pmap_copy_page(fs.m, fs.first_m);
1254 				vm_page_valid(fs.first_m);
1255 				if (wired && (fault_flags &
1256 				    VM_FAULT_WIRE) == 0) {
1257 					vm_page_wire(fs.first_m);
1258 					vm_page_unwire(fs.m, PQ_INACTIVE);
1259 				}
1260 				/*
1261 				 * Save the cow page to be released after
1262 				 * pmap_enter is complete.
1263 				 */
1264 				fs.m_cow = fs.m;
1265 				fs.m = NULL;
1266 			}
1267 			/*
1268 			 * fs.object != fs.first_object due to above
1269 			 * conditional
1270 			 */
1271 			vm_object_pip_wakeup(fs.object);
1272 
1273 			/*
1274 			 * We only try to prefault read-only mappings to the
1275 			 * neighboring pages when this copy-on-write fault is
1276 			 * a hard fault.  In other cases, trying to prefault
1277 			 * is typically wasted effort.
1278 			 */
1279 			if (faultcount == 0)
1280 				faultcount = 1;
1281 
1282 			/*
1283 			 * Only use the new page below...
1284 			 */
1285 			fs.object = fs.first_object;
1286 			fs.pindex = fs.first_pindex;
1287 			fs.m = fs.first_m;
1288 			if (!is_first_object_locked)
1289 				VM_OBJECT_WLOCK(fs.object);
1290 			VM_CNT_INC(v_cow_faults);
1291 			curthread->td_cow++;
1292 		} else {
1293 			prot &= ~VM_PROT_WRITE;
1294 		}
1295 	}
1296 
1297 	/*
1298 	 * We must verify that the maps have not changed since our last
1299 	 * lookup.
1300 	 */
1301 	if (!fs.lookup_still_valid) {
1302 		if (!vm_map_trylock_read(fs.map)) {
1303 			unlock_and_deallocate(&fs);
1304 			goto RetryFault;
1305 		}
1306 		fs.lookup_still_valid = true;
1307 		if (fs.map->timestamp != fs.map_generation) {
1308 			result = vm_map_lookup_locked(&fs.map, vaddr, fault_type,
1309 			    &fs.entry, &retry_object, &retry_pindex, &retry_prot, &wired);
1310 
1311 			/*
1312 			 * If we don't need the page any longer, put it on the inactive
1313 			 * list (the easiest thing to do here).  If no one needs it,
1314 			 * pageout will grab it eventually.
1315 			 */
1316 			if (result != KERN_SUCCESS) {
1317 				unlock_and_deallocate(&fs);
1318 
1319 				/*
1320 				 * If retry of map lookup would have blocked then
1321 				 * retry fault from start.
1322 				 */
1323 				if (result == KERN_FAILURE)
1324 					goto RetryFault;
1325 				return (result);
1326 			}
1327 			if ((retry_object != fs.first_object) ||
1328 			    (retry_pindex != fs.first_pindex)) {
1329 				unlock_and_deallocate(&fs);
1330 				goto RetryFault;
1331 			}
1332 
1333 			/*
1334 			 * Check whether the protection has changed or the object has
1335 			 * been copied while we left the map unlocked. Changing from
1336 			 * read to write permission is OK - we leave the page
1337 			 * write-protected, and catch the write fault. Changing from
1338 			 * write to read permission means that we can't mark the page
1339 			 * write-enabled after all.
1340 			 */
1341 			prot &= retry_prot;
1342 			fault_type &= retry_prot;
1343 			if (prot == 0) {
1344 				unlock_and_deallocate(&fs);
1345 				goto RetryFault;
1346 			}
1347 
1348 			/* Reassert because wired may have changed. */
1349 			KASSERT(wired || (fault_flags & VM_FAULT_WIRE) == 0,
1350 			    ("!wired && VM_FAULT_WIRE"));
1351 		}
1352 	}
1353 
1354 	/*
1355 	 * If the page was filled by a pager, save the virtual address that
1356 	 * should be faulted on next under a sequential access pattern to the
1357 	 * map entry.  A read lock on the map suffices to update this address
1358 	 * safely.
1359 	 */
1360 	if (hardfault)
1361 		fs.entry->next_read = vaddr + ptoa(ahead) + PAGE_SIZE;
1362 
1363 	vm_page_assert_xbusied(fs.m);
1364 	vm_fault_dirty(fs.entry, fs.m, prot, fault_type, fault_flags);
1365 
1366 	/*
1367 	 * Page must be completely valid or it is not fit to
1368 	 * map into user space.  vm_pager_get_pages() ensures this.
1369 	 */
1370 	KASSERT(vm_page_all_valid(fs.m),
1371 	    ("vm_fault: page %p partially invalid", fs.m));
1372 	VM_OBJECT_WUNLOCK(fs.object);
1373 
1374 	/*
1375 	 * Put this page into the physical map.  We had to do the unlock above
1376 	 * because pmap_enter() may sleep.  We don't put the page
1377 	 * back on the active queue until later so that the pageout daemon
1378 	 * won't find it (yet).
1379 	 */
1380 	pmap_enter(fs.map->pmap, vaddr, fs.m, prot,
1381 	    fault_type | (wired ? PMAP_ENTER_WIRED : 0), 0);
1382 	if (faultcount != 1 && (fault_flags & VM_FAULT_WIRE) == 0 &&
1383 	    wired == 0)
1384 		vm_fault_prefault(&fs, vaddr,
1385 		    faultcount > 0 ? behind : PFBAK,
1386 		    faultcount > 0 ? ahead : PFFOR, false);
1387 
1388 	/*
1389 	 * If the page is not wired down, then put it where the pageout daemon
1390 	 * can find it.
1391 	 */
1392 	if ((fault_flags & VM_FAULT_WIRE) != 0)
1393 		vm_page_wire(fs.m);
1394 	else
1395 		vm_page_activate(fs.m);
1396 	if (m_hold != NULL) {
1397 		*m_hold = fs.m;
1398 		vm_page_wire(fs.m);
1399 	}
1400 	vm_page_xunbusy(fs.m);
1401 	fs.m = NULL;
1402 
1403 	/*
1404 	 * Unlock everything, and return
1405 	 */
1406 	fault_deallocate(&fs);
1407 	if (hardfault) {
1408 		VM_CNT_INC(v_io_faults);
1409 		curthread->td_ru.ru_majflt++;
1410 #ifdef RACCT
1411 		if (racct_enable && fs.object->type == OBJT_VNODE) {
1412 			PROC_LOCK(curproc);
1413 			if ((fault_type & (VM_PROT_COPY | VM_PROT_WRITE)) != 0) {
1414 				racct_add_force(curproc, RACCT_WRITEBPS,
1415 				    PAGE_SIZE + behind * PAGE_SIZE);
1416 				racct_add_force(curproc, RACCT_WRITEIOPS, 1);
1417 			} else {
1418 				racct_add_force(curproc, RACCT_READBPS,
1419 				    PAGE_SIZE + ahead * PAGE_SIZE);
1420 				racct_add_force(curproc, RACCT_READIOPS, 1);
1421 			}
1422 			PROC_UNLOCK(curproc);
1423 		}
1424 #endif
1425 	} else
1426 		curthread->td_ru.ru_minflt++;
1427 
1428 	return (KERN_SUCCESS);
1429 }
1430 
1431 /*
1432  * Speed up the reclamation of pages that precede the faulting pindex within
1433  * the first object of the shadow chain.  Essentially, perform the equivalent
1434  * to madvise(..., MADV_DONTNEED) on a large cluster of pages that precedes
1435  * the faulting pindex by the cluster size when the pages read by vm_fault()
1436  * cross a cluster-size boundary.  The cluster size is the greater of the
1437  * smallest superpage size and VM_FAULT_DONTNEED_MIN.
1438  *
1439  * When "fs->first_object" is a shadow object, the pages in the backing object
1440  * that precede the faulting pindex are deactivated by vm_fault().  So, this
1441  * function must only be concerned with pages in the first object.
1442  */
1443 static void
1444 vm_fault_dontneed(const struct faultstate *fs, vm_offset_t vaddr, int ahead)
1445 {
1446 	vm_map_entry_t entry;
1447 	vm_object_t first_object, object;
1448 	vm_offset_t end, start;
1449 	vm_page_t m, m_next;
1450 	vm_pindex_t pend, pstart;
1451 	vm_size_t size;
1452 
1453 	object = fs->object;
1454 	VM_OBJECT_ASSERT_WLOCKED(object);
1455 	first_object = fs->first_object;
1456 	if (first_object != object) {
1457 		if (!VM_OBJECT_TRYWLOCK(first_object)) {
1458 			VM_OBJECT_WUNLOCK(object);
1459 			VM_OBJECT_WLOCK(first_object);
1460 			VM_OBJECT_WLOCK(object);
1461 		}
1462 	}
1463 	/* Neither fictitious nor unmanaged pages can be reclaimed. */
1464 	if ((first_object->flags & (OBJ_FICTITIOUS | OBJ_UNMANAGED)) == 0) {
1465 		size = VM_FAULT_DONTNEED_MIN;
1466 		if (MAXPAGESIZES > 1 && size < pagesizes[1])
1467 			size = pagesizes[1];
1468 		end = rounddown2(vaddr, size);
1469 		if (vaddr - end >= size - PAGE_SIZE - ptoa(ahead) &&
1470 		    (entry = fs->entry)->start < end) {
1471 			if (end - entry->start < size)
1472 				start = entry->start;
1473 			else
1474 				start = end - size;
1475 			pmap_advise(fs->map->pmap, start, end, MADV_DONTNEED);
1476 			pstart = OFF_TO_IDX(entry->offset) + atop(start -
1477 			    entry->start);
1478 			m_next = vm_page_find_least(first_object, pstart);
1479 			pend = OFF_TO_IDX(entry->offset) + atop(end -
1480 			    entry->start);
1481 			while ((m = m_next) != NULL && m->pindex < pend) {
1482 				m_next = TAILQ_NEXT(m, listq);
1483 				if (!vm_page_all_valid(m) ||
1484 				    vm_page_busied(m))
1485 					continue;
1486 
1487 				/*
1488 				 * Don't clear PGA_REFERENCED, since it would
1489 				 * likely represent a reference by a different
1490 				 * process.
1491 				 *
1492 				 * Typically, at this point, prefetched pages
1493 				 * are still in the inactive queue.  Only
1494 				 * pages that triggered page faults are in the
1495 				 * active queue.  The test for whether the page
1496 				 * is in the inactive queue is racy; in the
1497 				 * worst case we will requeue the page
1498 				 * unnecessarily.
1499 				 */
1500 				if (!vm_page_inactive(m))
1501 					vm_page_deactivate(m);
1502 			}
1503 		}
1504 	}
1505 	if (first_object != object)
1506 		VM_OBJECT_WUNLOCK(first_object);
1507 }
1508 
1509 /*
1510  * vm_fault_prefault provides a quick way of clustering
1511  * pagefaults into a processes address space.  It is a "cousin"
1512  * of vm_map_pmap_enter, except it runs at page fault time instead
1513  * of mmap time.
1514  */
1515 static void
1516 vm_fault_prefault(const struct faultstate *fs, vm_offset_t addra,
1517     int backward, int forward, bool obj_locked)
1518 {
1519 	pmap_t pmap;
1520 	vm_map_entry_t entry;
1521 	vm_object_t backing_object, lobject;
1522 	vm_offset_t addr, starta;
1523 	vm_pindex_t pindex;
1524 	vm_page_t m;
1525 	int i;
1526 
1527 	pmap = fs->map->pmap;
1528 	if (pmap != vmspace_pmap(curthread->td_proc->p_vmspace))
1529 		return;
1530 
1531 	entry = fs->entry;
1532 
1533 	if (addra < backward * PAGE_SIZE) {
1534 		starta = entry->start;
1535 	} else {
1536 		starta = addra - backward * PAGE_SIZE;
1537 		if (starta < entry->start)
1538 			starta = entry->start;
1539 	}
1540 
1541 	/*
1542 	 * Generate the sequence of virtual addresses that are candidates for
1543 	 * prefaulting in an outward spiral from the faulting virtual address,
1544 	 * "addra".  Specifically, the sequence is "addra - PAGE_SIZE", "addra
1545 	 * + PAGE_SIZE", "addra - 2 * PAGE_SIZE", "addra + 2 * PAGE_SIZE", ...
1546 	 * If the candidate address doesn't have a backing physical page, then
1547 	 * the loop immediately terminates.
1548 	 */
1549 	for (i = 0; i < 2 * imax(backward, forward); i++) {
1550 		addr = addra + ((i >> 1) + 1) * ((i & 1) == 0 ? -PAGE_SIZE :
1551 		    PAGE_SIZE);
1552 		if (addr > addra + forward * PAGE_SIZE)
1553 			addr = 0;
1554 
1555 		if (addr < starta || addr >= entry->end)
1556 			continue;
1557 
1558 		if (!pmap_is_prefaultable(pmap, addr))
1559 			continue;
1560 
1561 		pindex = ((addr - entry->start) + entry->offset) >> PAGE_SHIFT;
1562 		lobject = entry->object.vm_object;
1563 		if (!obj_locked)
1564 			VM_OBJECT_RLOCK(lobject);
1565 		while ((m = vm_page_lookup(lobject, pindex)) == NULL &&
1566 		    lobject->type == OBJT_DEFAULT &&
1567 		    (backing_object = lobject->backing_object) != NULL) {
1568 			KASSERT((lobject->backing_object_offset & PAGE_MASK) ==
1569 			    0, ("vm_fault_prefault: unaligned object offset"));
1570 			pindex += lobject->backing_object_offset >> PAGE_SHIFT;
1571 			VM_OBJECT_RLOCK(backing_object);
1572 			if (!obj_locked || lobject != entry->object.vm_object)
1573 				VM_OBJECT_RUNLOCK(lobject);
1574 			lobject = backing_object;
1575 		}
1576 		if (m == NULL) {
1577 			if (!obj_locked || lobject != entry->object.vm_object)
1578 				VM_OBJECT_RUNLOCK(lobject);
1579 			break;
1580 		}
1581 		if (vm_page_all_valid(m) &&
1582 		    (m->flags & PG_FICTITIOUS) == 0)
1583 			pmap_enter_quick(pmap, addr, m, entry->protection);
1584 		if (!obj_locked || lobject != entry->object.vm_object)
1585 			VM_OBJECT_RUNLOCK(lobject);
1586 	}
1587 }
1588 
1589 /*
1590  * Hold each of the physical pages that are mapped by the specified range of
1591  * virtual addresses, ["addr", "addr" + "len"), if those mappings are valid
1592  * and allow the specified types of access, "prot".  If all of the implied
1593  * pages are successfully held, then the number of held pages is returned
1594  * together with pointers to those pages in the array "ma".  However, if any
1595  * of the pages cannot be held, -1 is returned.
1596  */
1597 int
1598 vm_fault_quick_hold_pages(vm_map_t map, vm_offset_t addr, vm_size_t len,
1599     vm_prot_t prot, vm_page_t *ma, int max_count)
1600 {
1601 	vm_offset_t end, va;
1602 	vm_page_t *mp;
1603 	int count;
1604 	boolean_t pmap_failed;
1605 
1606 	if (len == 0)
1607 		return (0);
1608 	end = round_page(addr + len);
1609 	addr = trunc_page(addr);
1610 
1611 	/*
1612 	 * Check for illegal addresses.
1613 	 */
1614 	if (addr < vm_map_min(map) || addr > end || end > vm_map_max(map))
1615 		return (-1);
1616 
1617 	if (atop(end - addr) > max_count)
1618 		panic("vm_fault_quick_hold_pages: count > max_count");
1619 	count = atop(end - addr);
1620 
1621 	/*
1622 	 * Most likely, the physical pages are resident in the pmap, so it is
1623 	 * faster to try pmap_extract_and_hold() first.
1624 	 */
1625 	pmap_failed = FALSE;
1626 	for (mp = ma, va = addr; va < end; mp++, va += PAGE_SIZE) {
1627 		*mp = pmap_extract_and_hold(map->pmap, va, prot);
1628 		if (*mp == NULL)
1629 			pmap_failed = TRUE;
1630 		else if ((prot & VM_PROT_WRITE) != 0 &&
1631 		    (*mp)->dirty != VM_PAGE_BITS_ALL) {
1632 			/*
1633 			 * Explicitly dirty the physical page.  Otherwise, the
1634 			 * caller's changes may go unnoticed because they are
1635 			 * performed through an unmanaged mapping or by a DMA
1636 			 * operation.
1637 			 *
1638 			 * The object lock is not held here.
1639 			 * See vm_page_clear_dirty_mask().
1640 			 */
1641 			vm_page_dirty(*mp);
1642 		}
1643 	}
1644 	if (pmap_failed) {
1645 		/*
1646 		 * One or more pages could not be held by the pmap.  Either no
1647 		 * page was mapped at the specified virtual address or that
1648 		 * mapping had insufficient permissions.  Attempt to fault in
1649 		 * and hold these pages.
1650 		 *
1651 		 * If vm_fault_disable_pagefaults() was called,
1652 		 * i.e., TDP_NOFAULTING is set, we must not sleep nor
1653 		 * acquire MD VM locks, which means we must not call
1654 		 * vm_fault().  Some (out of tree) callers mark
1655 		 * too wide a code area with vm_fault_disable_pagefaults()
1656 		 * already, use the VM_PROT_QUICK_NOFAULT flag to request
1657 		 * the proper behaviour explicitly.
1658 		 */
1659 		if ((prot & VM_PROT_QUICK_NOFAULT) != 0 &&
1660 		    (curthread->td_pflags & TDP_NOFAULTING) != 0)
1661 			goto error;
1662 		for (mp = ma, va = addr; va < end; mp++, va += PAGE_SIZE)
1663 			if (*mp == NULL && vm_fault(map, va, prot,
1664 			    VM_FAULT_NORMAL, mp) != KERN_SUCCESS)
1665 				goto error;
1666 	}
1667 	return (count);
1668 error:
1669 	for (mp = ma; mp < ma + count; mp++)
1670 		if (*mp != NULL)
1671 			vm_page_unwire(*mp, PQ_INACTIVE);
1672 	return (-1);
1673 }
1674 
1675 /*
1676  *	Routine:
1677  *		vm_fault_copy_entry
1678  *	Function:
1679  *		Create new shadow object backing dst_entry with private copy of
1680  *		all underlying pages. When src_entry is equal to dst_entry,
1681  *		function implements COW for wired-down map entry. Otherwise,
1682  *		it forks wired entry into dst_map.
1683  *
1684  *	In/out conditions:
1685  *		The source and destination maps must be locked for write.
1686  *		The source map entry must be wired down (or be a sharing map
1687  *		entry corresponding to a main map entry that is wired down).
1688  */
1689 void
1690 vm_fault_copy_entry(vm_map_t dst_map, vm_map_t src_map,
1691     vm_map_entry_t dst_entry, vm_map_entry_t src_entry,
1692     vm_ooffset_t *fork_charge)
1693 {
1694 	vm_object_t backing_object, dst_object, object, src_object;
1695 	vm_pindex_t dst_pindex, pindex, src_pindex;
1696 	vm_prot_t access, prot;
1697 	vm_offset_t vaddr;
1698 	vm_page_t dst_m;
1699 	vm_page_t src_m;
1700 	boolean_t upgrade;
1701 
1702 #ifdef	lint
1703 	src_map++;
1704 #endif	/* lint */
1705 
1706 	upgrade = src_entry == dst_entry;
1707 	access = prot = dst_entry->protection;
1708 
1709 	src_object = src_entry->object.vm_object;
1710 	src_pindex = OFF_TO_IDX(src_entry->offset);
1711 
1712 	if (upgrade && (dst_entry->eflags & MAP_ENTRY_NEEDS_COPY) == 0) {
1713 		dst_object = src_object;
1714 		vm_object_reference(dst_object);
1715 	} else {
1716 		/*
1717 		 * Create the top-level object for the destination entry.
1718 		 * Doesn't actually shadow anything - we copy the pages
1719 		 * directly.
1720 		 */
1721 		dst_object = vm_object_allocate_anon(atop(dst_entry->end -
1722 		    dst_entry->start), NULL, NULL, 0);
1723 #if VM_NRESERVLEVEL > 0
1724 		dst_object->flags |= OBJ_COLORED;
1725 		dst_object->pg_color = atop(dst_entry->start);
1726 #endif
1727 		dst_object->domain = src_object->domain;
1728 		dst_object->charge = dst_entry->end - dst_entry->start;
1729 	}
1730 
1731 	VM_OBJECT_WLOCK(dst_object);
1732 	KASSERT(upgrade || dst_entry->object.vm_object == NULL,
1733 	    ("vm_fault_copy_entry: vm_object not NULL"));
1734 	if (src_object != dst_object) {
1735 		dst_entry->object.vm_object = dst_object;
1736 		dst_entry->offset = 0;
1737 		dst_entry->eflags &= ~MAP_ENTRY_VN_EXEC;
1738 	}
1739 	if (fork_charge != NULL) {
1740 		KASSERT(dst_entry->cred == NULL,
1741 		    ("vm_fault_copy_entry: leaked swp charge"));
1742 		dst_object->cred = curthread->td_ucred;
1743 		crhold(dst_object->cred);
1744 		*fork_charge += dst_object->charge;
1745 	} else if ((dst_object->type == OBJT_DEFAULT ||
1746 	    dst_object->type == OBJT_SWAP) &&
1747 	    dst_object->cred == NULL) {
1748 		KASSERT(dst_entry->cred != NULL, ("no cred for entry %p",
1749 		    dst_entry));
1750 		dst_object->cred = dst_entry->cred;
1751 		dst_entry->cred = NULL;
1752 	}
1753 
1754 	/*
1755 	 * If not an upgrade, then enter the mappings in the pmap as
1756 	 * read and/or execute accesses.  Otherwise, enter them as
1757 	 * write accesses.
1758 	 *
1759 	 * A writeable large page mapping is only created if all of
1760 	 * the constituent small page mappings are modified. Marking
1761 	 * PTEs as modified on inception allows promotion to happen
1762 	 * without taking potentially large number of soft faults.
1763 	 */
1764 	if (!upgrade)
1765 		access &= ~VM_PROT_WRITE;
1766 
1767 	/*
1768 	 * Loop through all of the virtual pages within the entry's
1769 	 * range, copying each page from the source object to the
1770 	 * destination object.  Since the source is wired, those pages
1771 	 * must exist.  In contrast, the destination is pageable.
1772 	 * Since the destination object doesn't share any backing storage
1773 	 * with the source object, all of its pages must be dirtied,
1774 	 * regardless of whether they can be written.
1775 	 */
1776 	for (vaddr = dst_entry->start, dst_pindex = 0;
1777 	    vaddr < dst_entry->end;
1778 	    vaddr += PAGE_SIZE, dst_pindex++) {
1779 again:
1780 		/*
1781 		 * Find the page in the source object, and copy it in.
1782 		 * Because the source is wired down, the page will be
1783 		 * in memory.
1784 		 */
1785 		if (src_object != dst_object)
1786 			VM_OBJECT_RLOCK(src_object);
1787 		object = src_object;
1788 		pindex = src_pindex + dst_pindex;
1789 		while ((src_m = vm_page_lookup(object, pindex)) == NULL &&
1790 		    (backing_object = object->backing_object) != NULL) {
1791 			/*
1792 			 * Unless the source mapping is read-only or
1793 			 * it is presently being upgraded from
1794 			 * read-only, the first object in the shadow
1795 			 * chain should provide all of the pages.  In
1796 			 * other words, this loop body should never be
1797 			 * executed when the source mapping is already
1798 			 * read/write.
1799 			 */
1800 			KASSERT((src_entry->protection & VM_PROT_WRITE) == 0 ||
1801 			    upgrade,
1802 			    ("vm_fault_copy_entry: main object missing page"));
1803 
1804 			VM_OBJECT_RLOCK(backing_object);
1805 			pindex += OFF_TO_IDX(object->backing_object_offset);
1806 			if (object != dst_object)
1807 				VM_OBJECT_RUNLOCK(object);
1808 			object = backing_object;
1809 		}
1810 		KASSERT(src_m != NULL, ("vm_fault_copy_entry: page missing"));
1811 
1812 		if (object != dst_object) {
1813 			/*
1814 			 * Allocate a page in the destination object.
1815 			 */
1816 			dst_m = vm_page_alloc(dst_object, (src_object ==
1817 			    dst_object ? src_pindex : 0) + dst_pindex,
1818 			    VM_ALLOC_NORMAL);
1819 			if (dst_m == NULL) {
1820 				VM_OBJECT_WUNLOCK(dst_object);
1821 				VM_OBJECT_RUNLOCK(object);
1822 				vm_wait(dst_object);
1823 				VM_OBJECT_WLOCK(dst_object);
1824 				goto again;
1825 			}
1826 			pmap_copy_page(src_m, dst_m);
1827 			VM_OBJECT_RUNLOCK(object);
1828 			dst_m->dirty = dst_m->valid = src_m->valid;
1829 		} else {
1830 			dst_m = src_m;
1831 			if (vm_page_busy_acquire(dst_m, VM_ALLOC_WAITFAIL) == 0)
1832 				goto again;
1833 			if (dst_m->pindex >= dst_object->size) {
1834 				/*
1835 				 * We are upgrading.  Index can occur
1836 				 * out of bounds if the object type is
1837 				 * vnode and the file was truncated.
1838 				 */
1839 				vm_page_xunbusy(dst_m);
1840 				break;
1841 			}
1842 		}
1843 		VM_OBJECT_WUNLOCK(dst_object);
1844 
1845 		/*
1846 		 * Enter it in the pmap. If a wired, copy-on-write
1847 		 * mapping is being replaced by a write-enabled
1848 		 * mapping, then wire that new mapping.
1849 		 *
1850 		 * The page can be invalid if the user called
1851 		 * msync(MS_INVALIDATE) or truncated the backing vnode
1852 		 * or shared memory object.  In this case, do not
1853 		 * insert it into pmap, but still do the copy so that
1854 		 * all copies of the wired map entry have similar
1855 		 * backing pages.
1856 		 */
1857 		if (vm_page_all_valid(dst_m)) {
1858 			pmap_enter(dst_map->pmap, vaddr, dst_m, prot,
1859 			    access | (upgrade ? PMAP_ENTER_WIRED : 0), 0);
1860 		}
1861 
1862 		/*
1863 		 * Mark it no longer busy, and put it on the active list.
1864 		 */
1865 		VM_OBJECT_WLOCK(dst_object);
1866 
1867 		if (upgrade) {
1868 			if (src_m != dst_m) {
1869 				vm_page_unwire(src_m, PQ_INACTIVE);
1870 				vm_page_wire(dst_m);
1871 			} else {
1872 				KASSERT(vm_page_wired(dst_m),
1873 				    ("dst_m %p is not wired", dst_m));
1874 			}
1875 		} else {
1876 			vm_page_activate(dst_m);
1877 		}
1878 		vm_page_xunbusy(dst_m);
1879 	}
1880 	VM_OBJECT_WUNLOCK(dst_object);
1881 	if (upgrade) {
1882 		dst_entry->eflags &= ~(MAP_ENTRY_COW | MAP_ENTRY_NEEDS_COPY);
1883 		vm_object_deallocate(src_object);
1884 	}
1885 }
1886 
1887 /*
1888  * Block entry into the machine-independent layer's page fault handler by
1889  * the calling thread.  Subsequent calls to vm_fault() by that thread will
1890  * return KERN_PROTECTION_FAILURE.  Enable machine-dependent handling of
1891  * spurious page faults.
1892  */
1893 int
1894 vm_fault_disable_pagefaults(void)
1895 {
1896 
1897 	return (curthread_pflags_set(TDP_NOFAULTING | TDP_RESETSPUR));
1898 }
1899 
1900 void
1901 vm_fault_enable_pagefaults(int save)
1902 {
1903 
1904 	curthread_pflags_restore(save);
1905 }
1906