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Achieve two goals at once: (1) Avoid an unnecessary broadcast TLB

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invalidation in pmap_remove_all(). (2) Prevent an "invalid ASID" assertion
failure in pmap_remove_all().

The architecture definition specifies that the TLB will not cache mappings
that don't have the "AF" bit set, so pmap_remove_all() needn't issue a TLB
invalidation for mappings that don't have the "AF" bit set.

We allocate ASIDs lazily.  Specifically, we don't allocate an ASID for a
pmap until we are activating it.  Now, consider what happens on a fork().
Before we activate the child's pmap, we use pmap_copy() to copy mappings
from the parent's pmap to the child's.  These new mappings have their "AF"
bits cleared.  Suppose that the page daemon decides to reclaim a page that
underlies one of these new mappings.  Previously, the pmap_invalidate_page()
performed by pmap_remove_all() on a mapping in the child's pmap would fail
an assertion because that pmap hasn't yet been assigned an ASID.  However,
we don't need to issue a TLB invalidation for such mappings because they
can't possibly be cached in the TLB.

Reported by:	bob prohaska <fbsd@www.zefox.net>
Reviewed by:	markj
MFC after:	1 week
X-MFC-before:	r354286
Differential Revision:	https://reviews.freebsd.org/D22388
This commit is contained in:
Alan Cox 2019-11-17 17:38:53 +00:00
parent 0857931660
commit 8a19cf92cf
Notes: svn2git 2020-12-20 02:59:44 +00:00 
svn path=/head/; revision=354792
1 changed files with 3 additions and 2 deletions
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5
sys/arm64/arm64/pmap.c
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@ -2879,11 +2879,12 @@ pmap_remove_all(vm_page_t m)
pte = pmap_l2_to_l3(pde, pv->pv_va);
tpte = pmap_load_clear(pte);
pmap_invalidate_page(pmap, pv->pv_va);
if (tpte & ATTR_SW_WIRED)
pmap->pm_stats.wired_count--;
if ((tpte & ATTR_AF) != 0)
if ((tpte & ATTR_AF) != 0) {
pmap_invalidate_page(pmap, pv->pv_va);
vm_page_aflag_set(m, PGA_REFERENCED);
}
/*
* Update the vm_page_t clean and reference bits.