Re: [PATCH v5 03/33] KVM: SVM: Flush the "current" TLB when activating AVIC

Maxim Levitsky
2023-01-08T14:26:03Z

On Fri, 2023-01-06 at 01:12 +0000, Sean Christopherson wrote:
> Flush the TLB when activating AVIC as the CPU can insert into the TLB
> while AVIC is "locally" disabled. KVM doesn't treat "APIC hardware
> disabled" as VM-wide AVIC inhibition, and so when a vCPU has its APIC
> hardware disabled, AVIC is not guaranteed to be inhibited. As a result,
> KVM may create a valid NPT mapping for the APIC base, which the CPU can
> cache as a non-AVIC translation.
>
> Note, Intel handles this in vmx_set_virtual_apic_mode().
>
> Reviewed-by: Paolo Bonzini <pbonzini@redhat.com>
> Cc: stable@vger.kernel.org
> Signed-off-by: Sean Christopherson <seanjc@google.com>
> ---
> arch/x86/kvm/svm/avic.c | 6 ++++++
> 1 file changed, 6 insertions(+)
>
> diff --git a/arch/x86/kvm/svm/avic.c b/arch/x86/kvm/svm/avic.c
> index 6919dee69f18..712330b80891 100644
> --- a/arch/x86/kvm/svm/avic.c
> +++ b/arch/x86/kvm/svm/avic.c
> @@ -86,6 +86,12 @@ static void avic_activate_vmcb(struct vcpu_svm *svm)
> /* Disabling MSR intercept for x2APIC registers */
> svm_set_x2apic_msr_interception(svm, false);
> } else {
> + /*
> + * Flush the TLB, the guest may have inserted a non-APIC
> + * mapping into the TLB while AVIC was disabled.
> + */
> + kvm_make_request(KVM_REQ_TLB_FLUSH_CURRENT, &svm->vcpu);
> +
> /* For xAVIC and hybrid-xAVIC modes */
> vmcb->control.avic_physical_id |= AVIC_MAX_PHYSICAL_ID;
> /* Enabling MSR intercept for x2APIC registers */

Reviewed-by: Maxim Levitsky <mlevitsk@redhat.com>

Best regards,
Maxim Levitsky