linux-kernel - Re: [PATCH v2 02/23] KVM: SVM: Flush the "current" TLB when activating AVIC

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Message-ID: <975d615b-8eb1-1d95-c753-7585c7aa9fac@redhat.com>
Date:   Mon, 5 Sep 2022 23:58:56 +0200
From:   Paolo Bonzini <pbonzini@...hat.com>
To:     Sean Christopherson <seanjc@...gle.com>
Cc:     kvm@...r.kernel.org, linux-kernel@...r.kernel.org,
        Suravee Suthikulpanit <suravee.suthikulpanit@....com>,
        Maxim Levitsky <mlevitsk@...hat.com>,
        Li RongQing <lirongqing@...du.com>
Subject: Re: [PATCH v2 02/23] KVM: SVM: Flush the "current" TLB when
 activating AVIC

On 9/3/22 02:22, 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().
> 
> Signed-off-by: Sean Christopherson <seanjc@...gle.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..4fbef2af1efc 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
> +		 * mappings into the TLB while AVIC was disabled.

mapping

Otherwise,

Reviewed-by: Paolo Bonzini <pbonzini@...hat.com>

Paolo

> +		 */
> +		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 */