2023-01-06 01:17:59

by Sean Christopherson

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

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 <[email protected]>
Cc: [email protected]
Signed-off-by: Sean Christopherson <[email protected]>
---
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 */
--
2.39.0.314.g84b9a713c41-goog

2023-01-08 14:50:25

by Maxim Levitsky

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

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 <[email protected]>
> Cc: [email protected]
> Signed-off-by: Sean Christopherson <[email protected]>
> ---
> 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 <[email protected]>

Best regards,
Maxim Levitsky