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vm_fault: only rely on PG_ZERO when the page was newly allocated

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If the fs->m page was found invalid on the object queue, PG_ZERO flag is
stale.  Track the source of the page in the new fault state variable
m_needs_zero, and ignore PG_ZERO if the page did not came from the
allocator.

Reviewed by:	markj
Tested by:	pho
Sponsored by:	The FreeBSD Foundation
MFC after:	1 week
Differential revision:	https://reviews.freebsd.org/D53963
This commit is contained in:
Konstantin Belousov 2025-11-28 17:57:22 +02:00
parent 636ee0269d
commit cff67bc43d
1 changed files with 5 additions and 1 deletions
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6
sys/vm/vm_fault.c
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@ -138,6 +138,7 @@ struct faultstate {
vm_object_t object;
vm_pindex_t pindex;
vm_page_t m;
bool m_needs_zeroing;
/* Top-level map object. */
vm_object_t first_object;
@ -273,6 +274,7 @@ static void
vm_fault_deallocate(struct faultstate *fs)
{
fs->m_needs_zeroing = true;
vm_fault_page_release(&fs->m_cow);
vm_fault_page_release(&fs->m);
vm_object_pip_wakeup(fs->object);
@ -1219,7 +1221,7 @@ vm_fault_zerofill(struct faultstate *fs)
/*
* Zero the page if necessary and mark it valid.
*/
if ((fs->m->flags & PG_ZERO) == 0) {
if (fs->m_needs_zeroing) {
pmap_zero_page(fs->m);
} else {
#ifdef INVARIANTS
@ -1352,6 +1354,7 @@ vm_fault_allocate(struct faultstate *fs, struct pctrie_iter *pages)
vm_waitpfault(dset, vm_pfault_oom_wait * hz);
return (FAULT_RESTART);
}
fs->m_needs_zeroing = (fs->m->flags & PG_ZERO) == 0;
fs->oom_started = false;
return (FAULT_CONTINUE);
@ -1686,6 +1689,7 @@ vm_fault(vm_map_t map, vm_offset_t vaddr, vm_prot_t fault_type,
fs.fault_flags = fault_flags;
fs.map = map;
fs.lookup_still_valid = false;
fs.m_needs_zeroing = true;
fs.oom_started = false;
fs.nera = -1;
fs.can_read_lock = true;