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KVM: X86: Move PTE present check from loop body to __shadow_walk_next()

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So far, the loop bodies already ensure the PTE is present before calling
__shadow_walk_next():  Some loop bodies simply exit with a !PRESENT
directly and some other loop bodies, i.e. FNAME(fetch) and __direct_map()
do not currently guard their walks with is_shadow_present_pte, but only
because they install present non-leaf SPTEs in the loop itself.

But checking pte present in __shadow_walk_next() (which is called from
shadow_walk_okay()) is more prudent; walking past a !PRESENT SPTE
would lead to attempting to read a the next level SPTE from a garbage
iter->shadow_addr.  It also allows to remove the is_shadow_present_pte()
checks from the loop bodies.

Reviewed-by: Sean Christopherson <seanjc@google.com>
Signed-off-by: Lai Jiangshan <laijs@linux.alibaba.com>
Message-Id: <20210906122547.263316-2-jiangshanlai@gmail.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
This commit is contained in:
Lai Jiangshan 2021-09-06 20:25:47 +08:00 committed by Paolo Bonzini
parent 5228eb96a4
commit 3e44dce4d0
2 changed files with 3 additions and 12 deletions
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13
arch/x86/kvm/mmu/mmu.c
View File

@ -2220,7 +2220,7 @@ static bool shadow_walk_okay(struct kvm_shadow_walk_iterator *iterator)
static void __shadow_walk_next(struct kvm_shadow_walk_iterator *iterator,
u64 spte)
{
if (is_last_spte(spte, iterator->level)) {
if (!is_shadow_present_pte(spte) || is_last_spte(spte, iterator->level)) {
iterator->level = 0;
return;
}
@ -3189,9 +3189,6 @@ static u64 *fast_pf_get_last_sptep(struct kvm_vcpu *vcpu, gpa_t gpa, u64 *spte)
for_each_shadow_entry_lockless(vcpu, gpa, iterator, old_spte) {
sptep = iterator.sptep;
*spte = old_spte;
if (!is_shadow_present_pte(old_spte))
break;
}
return sptep;
@ -3759,9 +3756,6 @@ static int get_walk(struct kvm_vcpu *vcpu, u64 addr, u64 *sptes, int *root_level
spte = mmu_spte_get_lockless(iterator.sptep);
sptes[leaf] = spte;
if (!is_shadow_present_pte(spte))
break;
}
return leaf;
@ -3877,11 +3871,8 @@ static void shadow_page_table_clear_flood(struct kvm_vcpu *vcpu, gva_t addr)
u64 spte;
walk_shadow_page_lockless_begin(vcpu);
for_each_shadow_entry_lockless(vcpu, addr, iterator, spte) {
for_each_shadow_entry_lockless(vcpu, addr, iterator, spte)
clear_sp_write_flooding_count(iterator.sptep);
if (!is_shadow_present_pte(spte))
break;
}
walk_shadow_page_lockless_end(vcpu);
}

2
arch/x86/kvm/mmu/paging_tmpl.h
View File

@ -1002,7 +1002,7 @@ static void FNAME(invlpg)(struct kvm_vcpu *vcpu, gva_t gva, hpa_t root_hpa)
FNAME(prefetch_gpte)(vcpu, sp, sptep, gpte, false);
}
if (!is_shadow_present_pte(*sptep) || !sp->unsync_children)
if (!sp->unsync_children)
break;
}
write_unlock(&vcpu->kvm->mmu_lock);