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SubjectRe: [PATCH v2 1/6] KVM: MMU: fix forgot flush vcpu tlbs
On Wed, Nov 17, 2010 at 06:26:51PM +0200, Avi Kivity wrote:
> On 11/17/2010 05:29 PM, Marcelo Tosatti wrote:
> >> diff --git a/arch/x86/kvm/paging_tmpl.h b/arch/x86/kvm/paging_tmpl.h
> >> index ba00eef..58b4d9a 100644
> >> --- a/arch/x86/kvm/paging_tmpl.h
> >> +++ b/arch/x86/kvm/paging_tmpl.h
> >> @@ -781,6 +781,7 @@ static int FNAME(sync_page)(struct kvm_vcpu *vcpu, struct kvm_mmu_page *sp,
> >> else
> >> nonpresent = shadow_notrap_nonpresent_pte;
> >> drop_spte(vcpu->kvm,&sp->spt[i], nonpresent);
> >> + kvm_flush_remote_tlbs(vcpu->kvm);
> >> continue;
> >> }
> >
> >This is not needed. Guest is responsible for flushing on
> >present->nonpresent change.
>
> sync_page
> drop_spte
> kvm_mmu_notifier_invalidate_page
> kvm_unmap_rmapp
> spte doesn't exist -> no flush
> page is freed
> guest can write into freed page?

Ugh right.

> I don't think we need to flush immediately; set a "tlb dirty" bit
> somewhere that is cleareded when we flush the tlb.
> kvm_mmu_notifier_invalidate_page() can consult the bit and force a
> flush if set.

Yep.



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