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freebsd-nq/sys/vm/vm_fault.c
Alan Cox 5730afc9b6 Handle spurious page faults that may occur in no-fault sections of the 
kernel.

When access restrictions are added to a page table entry, we flush the
corresponding virtual address mapping from the TLB.  In contrast, when
access restrictions are removed from a page table entry, we do not
flush the virtual address mapping from the TLB.  This is exactly as
recommended in AMD's documentation.  In effect, when access
restrictions are removed from a page table entry, AMD's MMUs will
transparently refresh a stale TLB entry.  In short, this saves us from
having to perform potentially costly TLB flushes.  In contrast,
Intel's MMUs are allowed to generate a spurious page fault based upon
the stale TLB entry.  Usually, such spurious page faults are handled
by vm_fault() without incident.  However, when we are executing
no-fault sections of the kernel, we are not allowed to execute
vm_fault().  This change introduces special-case handling for spurious
page faults that occur in no-fault sections of the kernel.

In collaboration with:	kib
Tested by:		gibbs (an earlier version)

I would also like to acknowledge Hiroki Sato's assistance in
diagnosing this problem.

MFC after:	1 week
2012-03-22 04:52:51 +00:00

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/*-
* Copyright (c) 1991, 1993
* The Regents of the University of California. All rights reserved.
* Copyright (c) 1994 John S. Dyson
* All rights reserved.
* Copyright (c) 1994 David Greenman
* All rights reserved.
*
*
* This code is derived from software contributed to Berkeley by
* The Mach Operating System project at Carnegie-Mellon University.
*
* Redistribution and use in source and binary forms, with or without
* modification, are permitted provided that the following conditions
* are met:
* 1. Redistributions of source code must retain the above copyright
* notice, this list of conditions and the following disclaimer.
* 2. Redistributions in binary form must reproduce the above copyright
* notice, this list of conditions and the following disclaimer in the
* documentation and/or other materials provided with the distribution.
* 3. All advertising materials mentioning features or use of this software
* must display the following acknowledgement:
* This product includes software developed by the University of
* California, Berkeley and its contributors.
* 4. Neither the name of the University nor the names of its contributors
* may be used to endorse or promote products derived from this software
* without specific prior written permission.
*
* THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
* ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
* IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
* ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
* FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
* DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
* OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
* HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
* LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
* OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
* SUCH DAMAGE.
*
* from: @(#)vm_fault.c 8.4 (Berkeley) 1/12/94
*
*
* Copyright (c) 1987, 1990 Carnegie-Mellon University.
* All rights reserved.
*
* Authors: Avadis Tevanian, Jr., Michael Wayne Young
*
* Permission to use, copy, modify and distribute this software and
* its documentation is hereby granted, provided that both the copyright
* notice and this permission notice appear in all copies of the
* software, derivative works or modified versions, and any portions
* thereof, and that both notices appear in supporting documentation.
*
* CARNEGIE MELLON ALLOWS FREE USE OF THIS SOFTWARE IN ITS "AS IS"
* CONDITION. CARNEGIE MELLON DISCLAIMS ANY LIABILITY OF ANY KIND
* FOR ANY DAMAGES WHATSOEVER RESULTING FROM THE USE OF THIS SOFTWARE.
*
* Carnegie Mellon requests users of this software to return to
*
* Software Distribution Coordinator or Software.Distribution@CS.CMU.EDU
* School of Computer Science
* Carnegie Mellon University
* Pittsburgh PA 15213-3890
*
* any improvements or extensions that they make and grant Carnegie the
* rights to redistribute these changes.
*/
/*
* Page fault handling module.
*/
#include <sys/cdefs.h>
__FBSDID("$FreeBSD$");
#include "opt_vm.h"
#include <sys/param.h>
#include <sys/systm.h>
#include <sys/kernel.h>
#include <sys/lock.h>
#include <sys/mutex.h>
#include <sys/proc.h>
#include <sys/resourcevar.h>
#include <sys/sysctl.h>
#include <sys/vmmeter.h>
#include <sys/vnode.h>
#include <vm/vm.h>
#include <vm/vm_param.h>
#include <vm/pmap.h>
#include <vm/vm_map.h>
#include <vm/vm_object.h>
#include <vm/vm_page.h>
#include <vm/vm_pageout.h>
#include <vm/vm_kern.h>
#include <vm/vm_pager.h>
#include <vm/vm_extern.h>
#include <sys/mount.h> /* XXX Temporary for VFS_LOCK_GIANT() */
#define PFBAK 4
#define PFFOR 4
#define PAGEORDER_SIZE (PFBAK+PFFOR)
static int prefault_pageorder[] = {
-1 * PAGE_SIZE, 1 * PAGE_SIZE,
-2 * PAGE_SIZE, 2 * PAGE_SIZE,
-3 * PAGE_SIZE, 3 * PAGE_SIZE,
-4 * PAGE_SIZE, 4 * PAGE_SIZE
};
static int vm_fault_additional_pages(vm_page_t, int, int, vm_page_t *, int *);
static void vm_fault_prefault(pmap_t, vm_offset_t, vm_map_entry_t);
#define VM_FAULT_READ_AHEAD 8
#define VM_FAULT_READ_BEHIND 7
#define VM_FAULT_READ (VM_FAULT_READ_AHEAD+VM_FAULT_READ_BEHIND+1)
struct faultstate {
vm_page_t m;
vm_object_t object;
vm_pindex_t pindex;
vm_page_t first_m;
vm_object_t first_object;
vm_pindex_t first_pindex;
vm_map_t map;
vm_map_entry_t entry;
int lookup_still_valid;
struct vnode *vp;
int vfslocked;
};
static inline void
release_page(struct faultstate *fs)
{
vm_page_wakeup(fs->m);
vm_page_lock(fs->m);
vm_page_deactivate(fs->m);
vm_page_unlock(fs->m);
fs->m = NULL;
}
static inline void
unlock_map(struct faultstate *fs)
{
if (fs->lookup_still_valid) {
vm_map_lookup_done(fs->map, fs->entry);
fs->lookup_still_valid = FALSE;
}
}
static void
unlock_and_deallocate(struct faultstate *fs)
{
vm_object_pip_wakeup(fs->object);
VM_OBJECT_UNLOCK(fs->object);
if (fs->object != fs->first_object) {
VM_OBJECT_LOCK(fs->first_object);
vm_page_lock(fs->first_m);
vm_page_free(fs->first_m);
vm_page_unlock(fs->first_m);
vm_object_pip_wakeup(fs->first_object);
VM_OBJECT_UNLOCK(fs->first_object);
fs->first_m = NULL;
}
vm_object_deallocate(fs->first_object);
unlock_map(fs);
if (fs->vp != NULL) {
vput(fs->vp);
fs->vp = NULL;
}
VFS_UNLOCK_GIANT(fs->vfslocked);
fs->vfslocked = 0;
}
/*
* TRYPAGER - used by vm_fault to calculate whether the pager for the
* current object *might* contain the page.
*
* default objects are zero-fill, there is no real pager.
*/
#define TRYPAGER (fs.object->type != OBJT_DEFAULT && \
((fault_flags & VM_FAULT_CHANGE_WIRING) == 0 || wired))
/*
* vm_fault:
*
* Handle a page fault occurring at the given address,
* requiring the given permissions, in the map specified.
* If successful, the page is inserted into the
* associated physical map.
*
* NOTE: the given address should be truncated to the
* proper page address.
*
* KERN_SUCCESS is returned if the page fault is handled; otherwise,
* a standard error specifying why the fault is fatal is returned.
*
* The map in question must be referenced, and remains so.
* Caller may hold no locks.
*/
int
vm_fault(vm_map_t map, vm_offset_t vaddr, vm_prot_t fault_type,
int fault_flags)
{
if ((curthread->td_pflags & TDP_NOFAULTING) != 0)
return (KERN_PROTECTION_FAILURE);
return (vm_fault_hold(map, vaddr, fault_type, fault_flags, NULL));
}
int
vm_fault_hold(vm_map_t map, vm_offset_t vaddr, vm_prot_t fault_type,
int fault_flags, vm_page_t *m_hold)
{
vm_prot_t prot;
int is_first_object_locked, result;
boolean_t growstack, wired;
int map_generation;
vm_object_t next_object;
vm_page_t marray[VM_FAULT_READ], mt, mt_prev;
int hardfault;
int faultcount, ahead, behind, alloc_req;
struct faultstate fs;
struct vnode *vp;
int locked, error;
hardfault = 0;
growstack = TRUE;
PCPU_INC(cnt.v_vm_faults);
fs.vp = NULL;
fs.vfslocked = 0;
faultcount = behind = 0;
RetryFault:;
/*
* Find the backing store object and offset into it to begin the
* search.
*/
fs.map = map;
result = vm_map_lookup(&fs.map, vaddr, fault_type, &fs.entry,
&fs.first_object, &fs.first_pindex, &prot, &wired);
if (result != KERN_SUCCESS) {
if (growstack && result == KERN_INVALID_ADDRESS &&
map != kernel_map) {
result = vm_map_growstack(curproc, vaddr);
if (result != KERN_SUCCESS)
return (KERN_FAILURE);
growstack = FALSE;
goto RetryFault;
}
return (result);
}
map_generation = fs.map->timestamp;
if (fs.entry->eflags & MAP_ENTRY_NOFAULT) {
panic("vm_fault: fault on nofault entry, addr: %lx",
(u_long)vaddr);
}
/*
* Make a reference to this object to prevent its disposal while we
* are messing with it. Once we have the reference, the map is free
* to be diddled. Since objects reference their shadows (and copies),
* they will stay around as well.
*
* Bump the paging-in-progress count to prevent size changes (e.g.
* truncation operations) during I/O. This must be done after
* obtaining the vnode lock in order to avoid possible deadlocks.
*/
VM_OBJECT_LOCK(fs.first_object);
vm_object_reference_locked(fs.first_object);
vm_object_pip_add(fs.first_object, 1);
fs.lookup_still_valid = TRUE;
if (wired)
fault_type = prot | (fault_type & VM_PROT_COPY);
fs.first_m = NULL;
/*
* Search for the page at object/offset.
*/
fs.object = fs.first_object;
fs.pindex = fs.first_pindex;
while (TRUE) {
/*
* If the object is dead, we stop here
*/
if (fs.object->flags & OBJ_DEAD) {
unlock_and_deallocate(&fs);
return (KERN_PROTECTION_FAILURE);
}
/*
* See if page is resident
*/
fs.m = vm_page_lookup(fs.object, fs.pindex);
if (fs.m != NULL) {
/*
* check for page-based copy on write.
* We check fs.object == fs.first_object so
* as to ensure the legacy COW mechanism is
* used when the page in question is part of
* a shadow object. Otherwise, vm_page_cowfault()
* removes the page from the backing object,
* which is not what we want.
*/
vm_page_lock(fs.m);
if ((fs.m->cow) &&
(fault_type & VM_PROT_WRITE) &&
(fs.object == fs.first_object)) {
vm_page_cowfault(fs.m);
unlock_and_deallocate(&fs);
goto RetryFault;
}
/*
* Wait/Retry if the page is busy. We have to do this
* if the page is busy via either VPO_BUSY or
* vm_page_t->busy because the vm_pager may be using
* vm_page_t->busy for pageouts ( and even pageins if
* it is the vnode pager ), and we could end up trying
* to pagein and pageout the same page simultaneously.
*
* We can theoretically allow the busy case on a read
* fault if the page is marked valid, but since such
* pages are typically already pmap'd, putting that
* special case in might be more effort then it is
* worth. We cannot under any circumstances mess
* around with a vm_page_t->busy page except, perhaps,
* to pmap it.
*/
if ((fs.m->oflags & VPO_BUSY) || fs.m->busy) {
/*
* Reference the page before unlocking and
* sleeping so that the page daemon is less
* likely to reclaim it.
*/
vm_page_aflag_set(fs.m, PGA_REFERENCED);
vm_page_unlock(fs.m);
if (fs.object != fs.first_object) {
if (!VM_OBJECT_TRYLOCK(
fs.first_object)) {
VM_OBJECT_UNLOCK(fs.object);
VM_OBJECT_LOCK(fs.first_object);
VM_OBJECT_LOCK(fs.object);
}
vm_page_lock(fs.first_m);
vm_page_free(fs.first_m);
vm_page_unlock(fs.first_m);
vm_object_pip_wakeup(fs.first_object);
VM_OBJECT_UNLOCK(fs.first_object);
fs.first_m = NULL;
}
unlock_map(&fs);
if (fs.m == vm_page_lookup(fs.object,
fs.pindex)) {
vm_page_sleep_if_busy(fs.m, TRUE,
"vmpfw");
}
vm_object_pip_wakeup(fs.object);
VM_OBJECT_UNLOCK(fs.object);
PCPU_INC(cnt.v_intrans);
vm_object_deallocate(fs.first_object);
goto RetryFault;
}
vm_pageq_remove(fs.m);
vm_page_unlock(fs.m);
/*
* Mark page busy for other processes, and the
* pagedaemon. If it still isn't completely valid
* (readable), jump to readrest, else break-out ( we
* found the page ).
*/
vm_page_busy(fs.m);
if (fs.m->valid != VM_PAGE_BITS_ALL)
goto readrest;
break;
}
/*
* Page is not resident, If this is the search termination
* or the pager might contain the page, allocate a new page.
*/
if (TRYPAGER || fs.object == fs.first_object) {
if (fs.pindex >= fs.object->size) {
unlock_and_deallocate(&fs);
return (KERN_PROTECTION_FAILURE);
}
/*
* Allocate a new page for this object/offset pair.
*
* Unlocked read of the p_flag is harmless. At
* worst, the P_KILLED might be not observed
* there, and allocation can fail, causing
* restart and new reading of the p_flag.
*/
fs.m = NULL;
if (!vm_page_count_severe() || P_KILLED(curproc)) {
#if VM_NRESERVLEVEL > 0
if ((fs.object->flags & OBJ_COLORED) == 0) {
fs.object->flags |= OBJ_COLORED;
fs.object->pg_color = atop(vaddr) -
fs.pindex;
}
#endif
alloc_req = P_KILLED(curproc) ?
VM_ALLOC_SYSTEM : VM_ALLOC_NORMAL;
if (fs.object->type != OBJT_VNODE &&
fs.object->backing_object == NULL)
alloc_req |= VM_ALLOC_ZERO;
fs.m = vm_page_alloc(fs.object, fs.pindex,
alloc_req);
}
if (fs.m == NULL) {
unlock_and_deallocate(&fs);
VM_WAITPFAULT;
goto RetryFault;
} else if (fs.m->valid == VM_PAGE_BITS_ALL)
break;
}
readrest:
/*
* We have found a valid page or we have allocated a new page.
* The page thus may not be valid or may not be entirely
* valid.
*
* Attempt to fault-in the page if there is a chance that the
* pager has it, and potentially fault in additional pages
* at the same time.
*/
if (TRYPAGER) {
int rv;
int reqpage = 0;
u_char behavior = vm_map_entry_behavior(fs.entry);
if (behavior == MAP_ENTRY_BEHAV_RANDOM ||
P_KILLED(curproc)) {
ahead = 0;
behind = 0;
} else {
behind = (vaddr - fs.entry->start) >> PAGE_SHIFT;
if (behind > VM_FAULT_READ_BEHIND)
behind = VM_FAULT_READ_BEHIND;
ahead = ((fs.entry->end - vaddr) >> PAGE_SHIFT) - 1;
if (ahead > VM_FAULT_READ_AHEAD)
ahead = VM_FAULT_READ_AHEAD;
}
is_first_object_locked = FALSE;
if ((behavior == MAP_ENTRY_BEHAV_SEQUENTIAL ||
(behavior != MAP_ENTRY_BEHAV_RANDOM &&
fs.pindex >= fs.entry->lastr &&
fs.pindex < fs.entry->lastr + VM_FAULT_READ)) &&
(fs.first_object == fs.object ||
(is_first_object_locked = VM_OBJECT_TRYLOCK(fs.first_object))) &&
fs.first_object->type != OBJT_DEVICE &&
fs.first_object->type != OBJT_PHYS &&
fs.first_object->type != OBJT_SG) {
vm_pindex_t firstpindex;
if (fs.first_pindex < 2 * VM_FAULT_READ)
firstpindex = 0;
else
firstpindex = fs.first_pindex - 2 * VM_FAULT_READ;
mt = fs.first_object != fs.object ?
fs.first_m : fs.m;
KASSERT(mt != NULL, ("vm_fault: missing mt"));
KASSERT((mt->oflags & VPO_BUSY) != 0,
("vm_fault: mt %p not busy", mt));
mt_prev = vm_page_prev(mt);
/*
* note: partially valid pages cannot be
* included in the lookahead - NFS piecemeal
* writes will barf on it badly.
*/
while ((mt = mt_prev) != NULL &&
mt->pindex >= firstpindex &&
mt->valid == VM_PAGE_BITS_ALL) {
mt_prev = vm_page_prev(mt);
if (mt->busy ||
(mt->oflags & VPO_BUSY))
continue;
vm_page_lock(mt);
if (mt->hold_count ||
mt->wire_count) {
vm_page_unlock(mt);
continue;
}
pmap_remove_all(mt);
if (mt->dirty != 0)
vm_page_deactivate(mt);
else
vm_page_cache(mt);
vm_page_unlock(mt);
}
ahead += behind;
behind = 0;
}
if (is_first_object_locked)
VM_OBJECT_UNLOCK(fs.first_object);
/*
* Call the pager to retrieve the data, if any, after
* releasing the lock on the map. We hold a ref on
* fs.object and the pages are VPO_BUSY'd.
*/
unlock_map(&fs);
vnode_lock:
if (fs.object->type == OBJT_VNODE) {
vp = fs.object->handle;
if (vp == fs.vp)
goto vnode_locked;
else if (fs.vp != NULL) {
vput(fs.vp);
fs.vp = NULL;
}
locked = VOP_ISLOCKED(vp);
if (VFS_NEEDSGIANT(vp->v_mount) && !fs.vfslocked) {
fs.vfslocked = 1;
if (!mtx_trylock(&Giant)) {
VM_OBJECT_UNLOCK(fs.object);
mtx_lock(&Giant);
VM_OBJECT_LOCK(fs.object);
goto vnode_lock;
}
}
if (locked != LK_EXCLUSIVE)
locked = LK_SHARED;
/* Do not sleep for vnode lock while fs.m is busy */
error = vget(vp, locked | LK_CANRECURSE |
LK_NOWAIT, curthread);
if (error != 0) {
int vfslocked;
vfslocked = fs.vfslocked;
fs.vfslocked = 0; /* Keep Giant */
vhold(vp);
release_page(&fs);
unlock_and_deallocate(&fs);
error = vget(vp, locked | LK_RETRY |
LK_CANRECURSE, curthread);
vdrop(vp);
fs.vp = vp;
fs.vfslocked = vfslocked;
KASSERT(error == 0,
("vm_fault: vget failed"));
goto RetryFault;
}
fs.vp = vp;
}
vnode_locked:
KASSERT(fs.vp == NULL || !fs.map->system_map,
("vm_fault: vnode-backed object mapped by system map"));
/*
* now we find out if any other pages should be paged
* in at this time this routine checks to see if the
* pages surrounding this fault reside in the same
* object as the page for this fault. If they do,
* then they are faulted in also into the object. The
* array "marray" returned contains an array of
* vm_page_t structs where one of them is the
* vm_page_t passed to the routine. The reqpage
* return value is the index into the marray for the
* vm_page_t passed to the routine.
*
* fs.m plus the additional pages are VPO_BUSY'd.
*/
faultcount = vm_fault_additional_pages(
fs.m, behind, ahead, marray, &reqpage);
rv = faultcount ?
vm_pager_get_pages(fs.object, marray, faultcount,
reqpage) : VM_PAGER_FAIL;
if (rv == VM_PAGER_OK) {
/*
* Found the page. Leave it busy while we play
* with it.
*/
/*
* Relookup in case pager changed page. Pager
* is responsible for disposition of old page
* if moved.
*/
fs.m = vm_page_lookup(fs.object, fs.pindex);
if (!fs.m) {
unlock_and_deallocate(&fs);
goto RetryFault;
}
hardfault++;
break; /* break to PAGE HAS BEEN FOUND */
}
/*
* Remove the bogus page (which does not exist at this
* object/offset); before doing so, we must get back
* our object lock to preserve our invariant.
*
* Also wake up any other process that may want to bring
* in this page.
*
* If this is the top-level object, we must leave the
* busy page to prevent another process from rushing
* past us, and inserting the page in that object at
* the same time that we are.
*/
if (rv == VM_PAGER_ERROR)
printf("vm_fault: pager read error, pid %d (%s)\n",
curproc->p_pid, curproc->p_comm);
/*
* Data outside the range of the pager or an I/O error
*/
/*
* XXX - the check for kernel_map is a kludge to work
* around having the machine panic on a kernel space
* fault w/ I/O error.
*/
if (((fs.map != kernel_map) && (rv == VM_PAGER_ERROR)) ||
(rv == VM_PAGER_BAD)) {
vm_page_lock(fs.m);
vm_page_free(fs.m);
vm_page_unlock(fs.m);
fs.m = NULL;
unlock_and_deallocate(&fs);
return ((rv == VM_PAGER_ERROR) ? KERN_FAILURE : KERN_PROTECTION_FAILURE);
}
if (fs.object != fs.first_object) {
vm_page_lock(fs.m);
vm_page_free(fs.m);
vm_page_unlock(fs.m);
fs.m = NULL;
/*
* XXX - we cannot just fall out at this
* point, m has been freed and is invalid!
*/
}
}
/*
* We get here if the object has default pager (or unwiring)
* or the pager doesn't have the page.
*/
if (fs.object == fs.first_object)
fs.first_m = fs.m;
/*
* Move on to the next object. Lock the next object before
* unlocking the current one.
*/
fs.pindex += OFF_TO_IDX(fs.object->backing_object_offset);
next_object = fs.object->backing_object;
if (next_object == NULL) {
/*
* If there's no object left, fill the page in the top
* object with zeros.
*/
if (fs.object != fs.first_object) {
vm_object_pip_wakeup(fs.object);
VM_OBJECT_UNLOCK(fs.object);
fs.object = fs.first_object;
fs.pindex = fs.first_pindex;
fs.m = fs.first_m;
VM_OBJECT_LOCK(fs.object);
}
fs.first_m = NULL;
/*
* Zero the page if necessary and mark it valid.
*/
if ((fs.m->flags & PG_ZERO) == 0) {
pmap_zero_page(fs.m);
} else {
PCPU_INC(cnt.v_ozfod);
}
PCPU_INC(cnt.v_zfod);
fs.m->valid = VM_PAGE_BITS_ALL;
break; /* break to PAGE HAS BEEN FOUND */
} else {
KASSERT(fs.object != next_object,
("object loop %p", next_object));
VM_OBJECT_LOCK(next_object);
vm_object_pip_add(next_object, 1);
if (fs.object != fs.first_object)
vm_object_pip_wakeup(fs.object);
VM_OBJECT_UNLOCK(fs.object);
fs.object = next_object;
}
}
KASSERT((fs.m->oflags & VPO_BUSY) != 0,
("vm_fault: not busy after main loop"));
/*
* PAGE HAS BEEN FOUND. [Loop invariant still holds -- the object lock
* is held.]
*/
/*
* If the page is being written, but isn't already owned by the
* top-level object, we have to copy it into a new page owned by the
* top-level object.
*/
if (fs.object != fs.first_object) {
/*
* We only really need to copy if we want to write it.
*/
if ((fault_type & (VM_PROT_COPY | VM_PROT_WRITE)) != 0) {
/*
* This allows pages to be virtually copied from a
* backing_object into the first_object, where the
* backing object has no other refs to it, and cannot
* gain any more refs. Instead of a bcopy, we just
* move the page from the backing object to the
* first object. Note that we must mark the page
* dirty in the first object so that it will go out
* to swap when needed.
*/
is_first_object_locked = FALSE;
if (
/*
* Only one shadow object
*/
(fs.object->shadow_count == 1) &&
/*
* No COW refs, except us
*/
(fs.object->ref_count == 1) &&
/*
* No one else can look this object up
*/
(fs.object->handle == NULL) &&
/*
* No other ways to look the object up
*/
((fs.object->type == OBJT_DEFAULT) ||
(fs.object->type == OBJT_SWAP)) &&
(is_first_object_locked = VM_OBJECT_TRYLOCK(fs.first_object)) &&
/*
* We don't chase down the shadow chain
*/
fs.object == fs.first_object->backing_object) {
/*
* get rid of the unnecessary page
*/
vm_page_lock(fs.first_m);
vm_page_free(fs.first_m);
vm_page_unlock(fs.first_m);
/*
* grab the page and put it into the
* process'es object. The page is
* automatically made dirty.
*/
vm_page_lock(fs.m);
vm_page_rename(fs.m, fs.first_object, fs.first_pindex);
vm_page_unlock(fs.m);
vm_page_busy(fs.m);
fs.first_m = fs.m;
fs.m = NULL;
PCPU_INC(cnt.v_cow_optim);
} else {
/*
* Oh, well, lets copy it.
*/
pmap_copy_page(fs.m, fs.first_m);
fs.first_m->valid = VM_PAGE_BITS_ALL;
if (wired && (fault_flags &
VM_FAULT_CHANGE_WIRING) == 0) {
vm_page_lock(fs.first_m);
vm_page_wire(fs.first_m);
vm_page_unlock(fs.first_m);
vm_page_lock(fs.m);
vm_page_unwire(fs.m, FALSE);
vm_page_unlock(fs.m);
}
/*
* We no longer need the old page or object.
*/
release_page(&fs);
}
/*
* fs.object != fs.first_object due to above
* conditional
*/
vm_object_pip_wakeup(fs.object);
VM_OBJECT_UNLOCK(fs.object);
/*
* Only use the new page below...
*/
fs.object = fs.first_object;
fs.pindex = fs.first_pindex;
fs.m = fs.first_m;
if (!is_first_object_locked)
VM_OBJECT_LOCK(fs.object);
PCPU_INC(cnt.v_cow_faults);
} else {
prot &= ~VM_PROT_WRITE;
}
}
/*
* We must verify that the maps have not changed since our last
* lookup.
*/
if (!fs.lookup_still_valid) {
vm_object_t retry_object;
vm_pindex_t retry_pindex;
vm_prot_t retry_prot;
if (!vm_map_trylock_read(fs.map)) {
release_page(&fs);
unlock_and_deallocate(&fs);
goto RetryFault;
}
fs.lookup_still_valid = TRUE;
if (fs.map->timestamp != map_generation) {
result = vm_map_lookup_locked(&fs.map, vaddr, fault_type,
&fs.entry, &retry_object, &retry_pindex, &retry_prot, &wired);
/*
* If we don't need the page any longer, put it on the inactive
* list (the easiest thing to do here). If no one needs it,
* pageout will grab it eventually.
*/
if (result != KERN_SUCCESS) {
release_page(&fs);
unlock_and_deallocate(&fs);
/*
* If retry of map lookup would have blocked then
* retry fault from start.
*/
if (result == KERN_FAILURE)
goto RetryFault;
return (result);
}
if ((retry_object != fs.first_object) ||
(retry_pindex != fs.first_pindex)) {
release_page(&fs);
unlock_and_deallocate(&fs);
goto RetryFault;
}
/*
* Check whether the protection has changed or the object has
* been copied while we left the map unlocked. Changing from
* read to write permission is OK - we leave the page
* write-protected, and catch the write fault. Changing from
* write to read permission means that we can't mark the page
* write-enabled after all.
*/
prot &= retry_prot;
}
}
/*
* If the page was filled by a pager, update the map entry's
* last read offset. Since the pager does not return the
* actual set of pages that it read, this update is based on
* the requested set. Typically, the requested and actual
* sets are the same.
*
* XXX The following assignment modifies the map
* without holding a write lock on it.
*/
if (hardfault)
fs.entry->lastr = fs.pindex + faultcount - behind;
if ((prot & VM_PROT_WRITE) != 0 ||
(fault_flags & VM_FAULT_DIRTY) != 0) {
vm_object_set_writeable_dirty(fs.object);
/*
* If this is a NOSYNC mmap we do not want to set VPO_NOSYNC
* if the page is already dirty to prevent data written with
* the expectation of being synced from not being synced.
* Likewise if this entry does not request NOSYNC then make
* sure the page isn't marked NOSYNC. Applications sharing
* data should use the same flags to avoid ping ponging.
*/
if (fs.entry->eflags & MAP_ENTRY_NOSYNC) {
if (fs.m->dirty == 0)
fs.m->oflags |= VPO_NOSYNC;
} else {
fs.m->oflags &= ~VPO_NOSYNC;
}
/*
* If the fault is a write, we know that this page is being
* written NOW so dirty it explicitly to save on
* pmap_is_modified() calls later.
*
* Also tell the backing pager, if any, that it should remove
* any swap backing since the page is now dirty.
*/
if (((fault_type & VM_PROT_WRITE) != 0 &&
(fault_flags & VM_FAULT_CHANGE_WIRING) == 0) ||
(fault_flags & VM_FAULT_DIRTY) != 0) {
vm_page_dirty(fs.m);
vm_pager_page_unswapped(fs.m);
}
}
/*
* Page had better still be busy
*/
KASSERT(fs.m->oflags & VPO_BUSY,
("vm_fault: page %p not busy!", fs.m));
/*
* Page must be completely valid or it is not fit to
* map into user space. vm_pager_get_pages() ensures this.
*/
KASSERT(fs.m->valid == VM_PAGE_BITS_ALL,
("vm_fault: page %p partially invalid", fs.m));
VM_OBJECT_UNLOCK(fs.object);
/*
* Put this page into the physical map. We had to do the unlock above
* because pmap_enter() may sleep. We don't put the page
* back on the active queue until later so that the pageout daemon
* won't find it (yet).
*/
pmap_enter(fs.map->pmap, vaddr, fault_type, fs.m, prot, wired);
if ((fault_flags & VM_FAULT_CHANGE_WIRING) == 0 && wired == 0)
vm_fault_prefault(fs.map->pmap, vaddr, fs.entry);
VM_OBJECT_LOCK(fs.object);
vm_page_lock(fs.m);
/*
* If the page is not wired down, then put it where the pageout daemon
* can find it.
*/
if (fault_flags & VM_FAULT_CHANGE_WIRING) {
if (wired)
vm_page_wire(fs.m);
else
vm_page_unwire(fs.m, 1);
} else
vm_page_activate(fs.m);
if (m_hold != NULL) {
*m_hold = fs.m;
vm_page_hold(fs.m);
}
vm_page_unlock(fs.m);
vm_page_wakeup(fs.m);
/*
* Unlock everything, and return
*/
unlock_and_deallocate(&fs);
if (hardfault)
curthread->td_ru.ru_majflt++;
else
curthread->td_ru.ru_minflt++;
return (KERN_SUCCESS);
}
/*
* vm_fault_prefault provides a quick way of clustering
* pagefaults into a processes address space. It is a "cousin"
* of vm_map_pmap_enter, except it runs at page fault time instead
* of mmap time.
*/
static void
vm_fault_prefault(pmap_t pmap, vm_offset_t addra, vm_map_entry_t entry)
{
int i;
vm_offset_t addr, starta;
vm_pindex_t pindex;
vm_page_t m;
vm_object_t object;
if (pmap != vmspace_pmap(curthread->td_proc->p_vmspace))
return;
object = entry->object.vm_object;
starta = addra - PFBAK * PAGE_SIZE;
if (starta < entry->start) {
starta = entry->start;
} else if (starta > addra) {
starta = 0;
}
for (i = 0; i < PAGEORDER_SIZE; i++) {
vm_object_t backing_object, lobject;
addr = addra + prefault_pageorder[i];
if (addr > addra + (PFFOR * PAGE_SIZE))
addr = 0;
if (addr < starta || addr >= entry->end)
continue;
if (!pmap_is_prefaultable(pmap, addr))
continue;
pindex = ((addr - entry->start) + entry->offset) >> PAGE_SHIFT;
lobject = object;
VM_OBJECT_LOCK(lobject);
while ((m = vm_page_lookup(lobject, pindex)) == NULL &&
lobject->type == OBJT_DEFAULT &&
(backing_object = lobject->backing_object) != NULL) {
KASSERT((lobject->backing_object_offset & PAGE_MASK) ==
0, ("vm_fault_prefault: unaligned object offset"));
pindex += lobject->backing_object_offset >> PAGE_SHIFT;
VM_OBJECT_LOCK(backing_object);
VM_OBJECT_UNLOCK(lobject);
lobject = backing_object;
}
/*
* give-up when a page is not in memory
*/
if (m == NULL) {
VM_OBJECT_UNLOCK(lobject);
break;
}
if (m->valid == VM_PAGE_BITS_ALL &&
(m->flags & PG_FICTITIOUS) == 0)
pmap_enter_quick(pmap, addr, m, entry->protection);
VM_OBJECT_UNLOCK(lobject);
}
}
/*
* Hold each of the physical pages that are mapped by the specified range of
* virtual addresses, ["addr", "addr" + "len"), if those mappings are valid
* and allow the specified types of access, "prot". If all of the implied
* pages are successfully held, then the number of held pages is returned
* together with pointers to those pages in the array "ma". However, if any
* of the pages cannot be held, -1 is returned.
*/
int
vm_fault_quick_hold_pages(vm_map_t map, vm_offset_t addr, vm_size_t len,
vm_prot_t prot, vm_page_t *ma, int max_count)
{
vm_offset_t end, va;
vm_page_t *mp;
int count;
boolean_t pmap_failed;
if (len == 0)
return (0);
end = round_page(addr + len);
addr = trunc_page(addr);
/*
* Check for illegal addresses.
*/
if (addr < vm_map_min(map) || addr > end || end > vm_map_max(map))
return (-1);
count = howmany(end - addr, PAGE_SIZE);
if (count > max_count)
panic("vm_fault_quick_hold_pages: count > max_count");
/*
* Most likely, the physical pages are resident in the pmap, so it is
* faster to try pmap_extract_and_hold() first.
*/
pmap_failed = FALSE;
for (mp = ma, va = addr; va < end; mp++, va += PAGE_SIZE) {
*mp = pmap_extract_and_hold(map->pmap, va, prot);
if (*mp == NULL)
pmap_failed = TRUE;
else if ((prot & VM_PROT_WRITE) != 0 &&
(*mp)->dirty != VM_PAGE_BITS_ALL) {
/*
* Explicitly dirty the physical page. Otherwise, the
* caller's changes may go unnoticed because they are
* performed through an unmanaged mapping or by a DMA
* operation.
*
* The object lock is not held here.
* See vm_page_clear_dirty_mask().
*/
vm_page_dirty(*mp);
}
}
if (pmap_failed) {
/*
* One or more pages could not be held by the pmap. Either no
* page was mapped at the specified virtual address or that
* mapping had insufficient permissions. Attempt to fault in
* and hold these pages.
*/
for (mp = ma, va = addr; va < end; mp++, va += PAGE_SIZE)
if (*mp == NULL && vm_fault_hold(map, va, prot,
VM_FAULT_NORMAL, mp) != KERN_SUCCESS)
goto error;
}
return (count);
error:
for (mp = ma; mp < ma + count; mp++)
if (*mp != NULL) {
vm_page_lock(*mp);
vm_page_unhold(*mp);
vm_page_unlock(*mp);
}
return (-1);
}
/*
* vm_fault_wire:
*
* Wire down a range of virtual addresses in a map.
*/
int
vm_fault_wire(vm_map_t map, vm_offset_t start, vm_offset_t end,
boolean_t fictitious)
{
vm_offset_t va;
int rv;
/*
* We simulate a fault to get the page and enter it in the physical
* map. For user wiring, we only ask for read access on currently
* read-only sections.
*/
for (va = start; va < end; va += PAGE_SIZE) {
rv = vm_fault(map, va, VM_PROT_NONE, VM_FAULT_CHANGE_WIRING);
if (rv) {
if (va != start)
vm_fault_unwire(map, start, va, fictitious);
return (rv);
}
}
return (KERN_SUCCESS);
}
/*
* vm_fault_unwire:
*
* Unwire a range of virtual addresses in a map.
*/
void
vm_fault_unwire(vm_map_t map, vm_offset_t start, vm_offset_t end,
boolean_t fictitious)
{
vm_paddr_t pa;
vm_offset_t va;
vm_page_t m;
pmap_t pmap;
pmap = vm_map_pmap(map);
/*
* Since the pages are wired down, we must be able to get their
* mappings from the physical map system.
*/
for (va = start; va < end; va += PAGE_SIZE) {
pa = pmap_extract(pmap, va);
if (pa != 0) {
pmap_change_wiring(pmap, va, FALSE);
if (!fictitious) {
m = PHYS_TO_VM_PAGE(pa);
vm_page_lock(m);
vm_page_unwire(m, TRUE);
vm_page_unlock(m);
}
}
}
}
/*
* Routine:
* vm_fault_copy_entry
* Function:
* Create new shadow object backing dst_entry with private copy of
* all underlying pages. When src_entry is equal to dst_entry,
* function implements COW for wired-down map entry. Otherwise,
* it forks wired entry into dst_map.
*
* In/out conditions:
* The source and destination maps must be locked for write.
* The source map entry must be wired down (or be a sharing map
* entry corresponding to a main map entry that is wired down).
*/
void
vm_fault_copy_entry(vm_map_t dst_map, vm_map_t src_map,
vm_map_entry_t dst_entry, vm_map_entry_t src_entry,
vm_ooffset_t *fork_charge)
{
vm_object_t backing_object, dst_object, object, src_object;
vm_pindex_t dst_pindex, pindex, src_pindex;
vm_prot_t access, prot;
vm_offset_t vaddr;
vm_page_t dst_m;
vm_page_t src_m;
boolean_t src_readonly, upgrade;
#ifdef lint
src_map++;
#endif /* lint */
upgrade = src_entry == dst_entry;
src_object = src_entry->object.vm_object;
src_pindex = OFF_TO_IDX(src_entry->offset);
src_readonly = (src_entry->protection & VM_PROT_WRITE) == 0;
/*
* Create the top-level object for the destination entry. (Doesn't
* actually shadow anything - we copy the pages directly.)
*/
dst_object = vm_object_allocate(OBJT_DEFAULT,
OFF_TO_IDX(dst_entry->end - dst_entry->start));
#if VM_NRESERVLEVEL > 0
dst_object->flags |= OBJ_COLORED;
dst_object->pg_color = atop(dst_entry->start);
#endif
VM_OBJECT_LOCK(dst_object);
KASSERT(upgrade || dst_entry->object.vm_object == NULL,
("vm_fault_copy_entry: vm_object not NULL"));
dst_entry->object.vm_object = dst_object;
dst_entry->offset = 0;
dst_object->charge = dst_entry->end - dst_entry->start;
if (fork_charge != NULL) {
KASSERT(dst_entry->cred == NULL,
("vm_fault_copy_entry: leaked swp charge"));
dst_object->cred = curthread->td_ucred;
crhold(dst_object->cred);
*fork_charge += dst_object->charge;
} else {
dst_object->cred = dst_entry->cred;
dst_entry->cred = NULL;
}
access = prot = dst_entry->protection;
/*
* If not an upgrade, then enter the mappings in the pmap as
* read and/or execute accesses. Otherwise, enter them as
* write accesses.
*
* A writeable large page mapping is only created if all of
* the constituent small page mappings are modified. Marking
* PTEs as modified on inception allows promotion to happen
* without taking potentially large number of soft faults.
*/
if (!upgrade)
access &= ~VM_PROT_WRITE;
/*
* Loop through all of the pages in the entry's range, copying each
* one from the source object (it should be there) to the destination
* object.
*/
for (vaddr = dst_entry->start, dst_pindex = 0;
vaddr < dst_entry->end;
vaddr += PAGE_SIZE, dst_pindex++) {
/*
* Allocate a page in the destination object.
*/
do {
dst_m = vm_page_alloc(dst_object, dst_pindex,
VM_ALLOC_NORMAL);
if (dst_m == NULL) {
VM_OBJECT_UNLOCK(dst_object);
VM_WAIT;
VM_OBJECT_LOCK(dst_object);
}
} while (dst_m == NULL);
/*
* Find the page in the source object, and copy it in.
* (Because the source is wired down, the page will be in
* memory.)
*/
VM_OBJECT_LOCK(src_object);
object = src_object;
pindex = src_pindex + dst_pindex;
while ((src_m = vm_page_lookup(object, pindex)) == NULL &&
src_readonly &&
(backing_object = object->backing_object) != NULL) {
/*
* Allow fallback to backing objects if we are reading.
*/
VM_OBJECT_LOCK(backing_object);
pindex += OFF_TO_IDX(object->backing_object_offset);
VM_OBJECT_UNLOCK(object);
object = backing_object;
}
if (src_m == NULL)
panic("vm_fault_copy_wired: page missing");
pmap_copy_page(src_m, dst_m);
VM_OBJECT_UNLOCK(object);
dst_m->valid = VM_PAGE_BITS_ALL;
VM_OBJECT_UNLOCK(dst_object);
/*
* Enter it in the pmap. If a wired, copy-on-write
* mapping is being replaced by a write-enabled
* mapping, then wire that new mapping.
*/
pmap_enter(dst_map->pmap, vaddr, access, dst_m, prot, upgrade);
/*
* Mark it no longer busy, and put it on the active list.
*/
VM_OBJECT_LOCK(dst_object);
if (upgrade) {
vm_page_lock(src_m);
vm_page_unwire(src_m, 0);
vm_page_unlock(src_m);
vm_page_lock(dst_m);
vm_page_wire(dst_m);
vm_page_unlock(dst_m);
} else {
vm_page_lock(dst_m);
vm_page_activate(dst_m);
vm_page_unlock(dst_m);
}
vm_page_wakeup(dst_m);
}
VM_OBJECT_UNLOCK(dst_object);
if (upgrade) {
dst_entry->eflags &= ~(MAP_ENTRY_COW | MAP_ENTRY_NEEDS_COPY);
vm_object_deallocate(src_object);
}
}
/*
* This routine checks around the requested page for other pages that
* might be able to be faulted in. This routine brackets the viable
* pages for the pages to be paged in.
*
* Inputs:
* m, rbehind, rahead
*
* Outputs:
* marray (array of vm_page_t), reqpage (index of requested page)
*
* Return value:
* number of pages in marray
*/
static int
vm_fault_additional_pages(m, rbehind, rahead, marray, reqpage)
vm_page_t m;
int rbehind;
int rahead;
vm_page_t *marray;
int *reqpage;
{
int i,j;
vm_object_t object;
vm_pindex_t pindex, startpindex, endpindex, tpindex;
vm_page_t rtm;
int cbehind, cahead;
VM_OBJECT_LOCK_ASSERT(m->object, MA_OWNED);
object = m->object;
pindex = m->pindex;
cbehind = cahead = 0;
/*
* if the requested page is not available, then give up now
*/
if (!vm_pager_has_page(object, pindex, &cbehind, &cahead)) {
return 0;
}
if ((cbehind == 0) && (cahead == 0)) {
*reqpage = 0;
marray[0] = m;
return 1;
}
if (rahead > cahead) {
rahead = cahead;
}
if (rbehind > cbehind) {
rbehind = cbehind;
}
/*
* scan backward for the read behind pages -- in memory
*/
if (pindex > 0) {
if (rbehind > pindex) {
rbehind = pindex;
startpindex = 0;
} else {
startpindex = pindex - rbehind;
}
if ((rtm = TAILQ_PREV(m, pglist, listq)) != NULL &&
rtm->pindex >= startpindex)
startpindex = rtm->pindex + 1;
/* tpindex is unsigned; beware of numeric underflow. */
for (i = 0, tpindex = pindex - 1; tpindex >= startpindex &&
tpindex < pindex; i++, tpindex--) {
rtm = vm_page_alloc(object, tpindex, VM_ALLOC_NORMAL |
VM_ALLOC_IFNOTCACHED);
if (rtm == NULL) {
/*
* Shift the allocated pages to the
* beginning of the array.
*/
for (j = 0; j < i; j++) {
marray[j] = marray[j + tpindex + 1 -
startpindex];
}
break;
}
marray[tpindex - startpindex] = rtm;
}
} else {
startpindex = 0;
i = 0;
}
marray[i] = m;
/* page offset of the required page */
*reqpage = i;
tpindex = pindex + 1;
i++;
/*
* scan forward for the read ahead pages
*/
endpindex = tpindex + rahead;
if ((rtm = TAILQ_NEXT(m, listq)) != NULL && rtm->pindex < endpindex)
endpindex = rtm->pindex;
if (endpindex > object->size)
endpindex = object->size;
for (; tpindex < endpindex; i++, tpindex++) {
rtm = vm_page_alloc(object, tpindex, VM_ALLOC_NORMAL |
VM_ALLOC_IFNOTCACHED);
if (rtm == NULL) {
break;
}
marray[i] = rtm;
}
/* return number of pages */
return i;
}
/*
* Block entry into the machine-independent layer's page fault handler by
* the calling thread. Subsequent calls to vm_fault() by that thread will
* return KERN_PROTECTION_FAILURE. Enable machine-dependent handling of
* spurious page faults.
*/
int
vm_fault_disable_pagefaults(void)
{
return (curthread_pflags_set(TDP_NOFAULTING | TDP_RESETSPUR));
}
void
vm_fault_enable_pagefaults(int save)
{
curthread_pflags_restore(save);
}
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