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Invalidate the mapping before updating its physical address.

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Doing so ensures that all threads sharing the pmap have a consistent
view of the mapping.  This fixes the problem described in the commit
log messages for r329254 without the overhead of an extra fault in the
common case.  Once other pmap_enter() implementations are similarly
modified, the workaround added in r329254 can be removed, reducing the
overhead of CoW faults.

See also r335784 for amd64.  The i386 implementation of pmap_enter()
already reused the PV entry from the old mapping.

Reviewed by:	kib, markj
Tested by:	pho
MFC after:	3 weeks
Differential Revision:	https://reviews.freebsd.org/D16133
This commit is contained in:
alc 2018-07-08 16:51:54 +00:00
parent 3e02c9db48
commit f3d2853f4b
1 changed files with 43 additions and 27 deletions
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70
sys/i386/i386/pmap.c
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@ -3636,7 +3636,6 @@ pmap_enter(pmap_t pmap, vm_offset_t va, vm_page_t m, vm_prot_t prot,
}
pa = VM_PAGE_TO_PHYS(m);
om = NULL;
origpte = *pte;
opa = origpte & PG_FRAME;
@ -3661,10 +3660,8 @@ pmap_enter(pmap_t pmap, vm_offset_t va, vm_page_t m, vm_prot_t prot,
if (mpte)
mpte->wire_count--;
if (origpte & PG_MANAGED) {
om = m;
if (origpte & PG_MANAGED)
pa |= PG_MANAGED;
}
goto validate;
}
@ -3672,15 +3669,42 @@ pmap_enter(pmap_t pmap, vm_offset_t va, vm_page_t m, vm_prot_t prot,
/*
* Mapping has changed, invalidate old range and fall through to
* handle validating new mapping.
* handle validating new mapping. This ensures that all threads
* sharing the pmap keep a consistent view of the mapping, which is
* necessary for the correct handling of COW faults. It
* also permits reuse of the old mapping's PV entry,
* avoiding an allocation.
*
* For consistency, handle unmanaged mappings the same way.
*/
if (opa) {
origpte = pte_load_clear(pte);
KASSERT((origpte & PG_FRAME) == opa,
("pmap_enter: unexpected pa update for %#x", va));
if (origpte & PG_W)
pmap->pm_stats.wired_count--;
if (origpte & PG_MANAGED) {
om = PHYS_TO_VM_PAGE(opa);
/*
* The pmap lock is sufficient to synchronize with
* concurrent calls to pmap_page_test_mappings() and
* pmap_ts_referenced().
*/
if ((origpte & (PG_M | PG_RW)) == (PG_M | PG_RW))
vm_page_dirty(om);
if ((origpte & PG_A) != 0)
vm_page_aflag_set(om, PGA_REFERENCED);
pv = pmap_pvh_remove(&om->md, pmap, va);
if ((om->aflags & PGA_WRITEABLE) != 0 &&
TAILQ_EMPTY(&om->md.pv_list) &&
((om->flags & PG_FICTITIOUS) != 0 ||
TAILQ_EMPTY(&pa_to_pvh(opa)->pv_list)))
vm_page_aflag_clear(om, PGA_WRITEABLE);
}
if ((origpte & PG_A) != 0)
pmap_invalidate_page(pmap, va);
origpte = 0;
if (mpte != NULL) {
mpte->wire_count--;
KASSERT(mpte->wire_count > 0,
@ -3697,9 +3721,10 @@ pmap_enter(pmap_t pmap, vm_offset_t va, vm_page_t m, vm_prot_t prot,
KASSERT(pmap != kernel_pmap || va < kmi.clean_sva ||
va >= kmi.clean_eva,
("pmap_enter: managed mapping within the clean submap"));
if (pv == NULL)
if (pv == NULL) {
pv = get_pv_entry(pmap, FALSE);
pv->pv_va = va;
pv->pv_va = va;
}
TAILQ_INSERT_TAIL(&m->md.pv_list, pv, pv_next);
pa |= PG_MANAGED;
} else if (pv != NULL)
@ -3741,28 +3766,19 @@ validate:
if (origpte & PG_V) {
invlva = FALSE;
origpte = pte_load_store(pte, newpte);
if (origpte & PG_A) {
if (origpte & PG_MANAGED)
vm_page_aflag_set(om, PGA_REFERENCED);
if (opa != VM_PAGE_TO_PHYS(m))
invlva = TRUE;
#if defined(PAE) || defined(PAE_TABLES)
if ((origpte & PG_NX) == 0 &&
(newpte & PG_NX) != 0)
invlva = TRUE;
#endif
}
if ((origpte & (PG_M | PG_RW)) == (PG_M | PG_RW)) {
KASSERT((origpte & PG_FRAME) == VM_PAGE_TO_PHYS(m),
("pmap_enter: unexpected pa update for %#x", va));
if ((origpte & (PG_M | PG_RW)) == (PG_M | PG_RW) &&
(newpte & PG_M) == 0) {
if ((origpte & PG_MANAGED) != 0)
vm_page_dirty(om);
if ((prot & VM_PROT_WRITE) == 0)
invlva = TRUE;
vm_page_dirty(m);
invlva = TRUE;
}
if ((origpte & PG_MANAGED) != 0 &&
TAILQ_EMPTY(&om->md.pv_list) &&
((om->flags & PG_FICTITIOUS) != 0 ||
TAILQ_EMPTY(&pa_to_pvh(opa)->pv_list)))
vm_page_aflag_clear(om, PGA_WRITEABLE);
#if defined(PAE) || defined(PAE_TABLES)
else if ((origpte & (PG_A | PG_NX)) == PG_A &&
(newpte & PG_NX) != 0)
invlva = TRUE;
#endif
if (invlva)
pmap_invalidate_page(pmap, va);
} else