linux-kernel - Re: [PATCH 2/2] KVM: SVM: Set/clear CR8 write interception when AVIC is (de)activated

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Message-ID: <aYYq9u7bZWsmJNMr@google.com>
Date: Fri, 6 Feb 2026 09:55:02 -0800
From: Sean Christopherson <seanjc@...gle.com>
To: Naveen N Rao <naveen@...nel.org>
Cc: Paolo Bonzini <pbonzini@...hat.com>, kvm@...r.kernel.org, linux-kernel@...r.kernel.org, 
	Jim Mattson <jmattson@...gle.com>, "Maciej S . Szmigiero" <maciej.szmigiero@...cle.com>
Subject: Re: [PATCH 2/2] KVM: SVM: Set/clear CR8 write interception when AVIC
 is (de)activated

On Fri, Feb 06, 2026, Naveen N Rao wrote:
> On Tue, Feb 03, 2026 at 11:07:10AM -0800, Sean Christopherson wrote:
> > Explicitly set/clear CR8 write interception when AVIC is (de)activated to
> > fix a bug where KVM leaves the interception enabled after AVIC is
> > activated.  E.g. if KVM emulates INIT=>WFS while AVIC is deactivated, CR8
> > will remain intercepted in perpetuity.
> 
> Looking at svm_update_cr8_intercept(), I suppose this could also more 
> commonly happen whenever AVIC is inhibited (IRQ Windows, as an example)?

Maybe?  I don't think it's actually common in practice.  Because the bug requires
the source of the inhibition to be removed while the vCPU still has a pending IRQ
that is below PPR.  Which is definitely possible, but that seems overall unlikely,
and it'd also be self-healing to some extent.  E.g. if a workload is triggering
ExtINT, then odds are good it's going to _keep_ generating ExtINT, keep toggling
the inhibit, and thus reconcile CR8 interception every time AVIC is inhibited.