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SubjectRe: [PATCH v2 31/32] KVM: nVMX: Don't flush TLB on nested VM transition with EPT enabled
On Tue, Mar 17, 2020 at 06:18:37PM +0100, Paolo Bonzini wrote:
> On 17/03/20 05:52, Sean Christopherson wrote:
> > diff --git a/arch/x86/kvm/vmx/nested.c b/arch/x86/kvm/vmx/nested.c
> > index d816f1366943..a77eab5b0e8a 100644
> > --- a/arch/x86/kvm/vmx/nested.c
> > +++ b/arch/x86/kvm/vmx/nested.c
> > @@ -1123,7 +1123,7 @@ static int nested_vmx_load_cr3(struct kvm_vcpu *vcpu, unsigned long cr3, bool ne
> > }
> >
> > if (!nested_ept)
> > - kvm_mmu_new_cr3(vcpu, cr3, false);
> > + kvm_mmu_new_cr3(vcpu, cr3, enable_ept);
>
> Even if enable_ept == false, we could have already scheduled or flushed
> the TLB soon due to one of 1) nested_vmx_transition_tlb_flush 2)
> vpid_sync_context in prepare_vmcs02 3) the processor doing it for
> !enable_vpid.
>
> So for !enable_ept only KVM_REQ_MMU_SYNC is needed, not
> KVM_REQ_TLB_FLUSH_CURRENT I think. Worth adding a TODO?

Now that you point it out, I think it makes sense to unconditionally pass
%true here, i.e. rely 100% on nested_vmx_transition_tlb_flush() to do the
right thing.

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