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KVM: X86: Fix missed remote tlb flush in rmap_write_protect() 

When kvm->tlbs_dirty > 0, some rmaps might have been deleted
without flushing tlb remotely after kvm_sync_page().  If @gfn
was writable before and it's rmaps was deleted in kvm_sync_page(),
and if the tlb entry is still in a remote running VCPU,  the @gfn
is not safely protected.

To fix the problem, kvm_sync_page() does the remote flush when
needed to avoid the problem.

Fixes: a4ee1ca4a3 ("KVM: MMU: delay flush all tlbs on sync_page path")
Signed-off-by: Lai Jiangshan <laijs@linux.alibaba.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Message-Id: <20210918005636.3675-2-jiangshanlai@gmail.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
This commit is contained in:
Lai Jiangshan 2021-09-18 08:56:27 +08:00 committed by Paolo Bonzini
parent faf6b75562
commit f81602958c
1 changed files with 2 additions and 21 deletions
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23
arch/x86/kvm/mmu/paging_tmpl.h
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@ -1047,14 +1047,6 @@ static gpa_t FNAME(gva_to_gpa_nested)(struct kvm_vcpu *vcpu, gpa_t vaddr,
* Using the cached information from sp->gfns is safe because:
* - The spte has a reference to the struct page, so the pfn for a given gfn
* can't change unless all sptes pointing to it are nuked first.
*
* Note:
* We should flush all tlbs if spte is dropped even though guest is
* responsible for it. Since if we don't, kvm_mmu_notifier_invalidate_page
* and kvm_mmu_notifier_invalidate_range_start detect the mapping page isn't
* used by guest then tlbs are not flushed, so guest is allowed to access the
* freed pages.
* And we increase kvm->tlbs_dirty to delay tlbs flush in this case.
*/
static int FNAME(sync_page)(struct kvm_vcpu *vcpu, struct kvm_mmu_page *sp)
{
@ -1107,13 +1099,7 @@ static int FNAME(sync_page)(struct kvm_vcpu *vcpu, struct kvm_mmu_page *sp)
return 0;
if (FNAME(prefetch_invalid_gpte)(vcpu, sp, &sp->spt[i], gpte)) {
/*
* Update spte before increasing tlbs_dirty to make
* sure no tlb flush is lost after spte is zapped; see
* the comments in kvm_flush_remote_tlbs().
*/
smp_wmb();
vcpu->kvm->tlbs_dirty++;
set_spte_ret |= SET_SPTE_NEED_REMOTE_TLB_FLUSH;
continue;
}
@ -1128,12 +1114,7 @@ static int FNAME(sync_page)(struct kvm_vcpu *vcpu, struct kvm_mmu_page *sp)
if (gfn != sp->gfns[i]) {
drop_spte(vcpu->kvm, &sp->spt[i]);
/*
* The same as above where we are doing
* prefetch_invalid_gpte().
*/
smp_wmb();
vcpu->kvm->tlbs_dirty++;
set_spte_ret |= SET_SPTE_NEED_REMOTE_TLB_FLUSH;
continue;
}