linux-kernel - Re: [PATCH v3 18/62] KVM: SVM: Disable (x2)AVIC IPI virtualization if CPU has erratum #1235

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Message-ID: <aFly_5c0aqTOGEem@google.com>
Date: Mon, 23 Jun 2025 08:30:07 -0700
From: Sean Christopherson <seanjc@...gle.com>
To: Naveen N Rao <naveen@...nel.org>
Cc: Marc Zyngier <maz@...nel.org>, Oliver Upton <oliver.upton@...ux.dev>, 
	Paolo Bonzini <pbonzini@...hat.com>, Joerg Roedel <joro@...tes.org>, 
	David Woodhouse <dwmw2@...radead.org>, Lu Baolu <baolu.lu@...ux.intel.com>, 
	linux-arm-kernel@...ts.infradead.org, kvmarm@...ts.linux.dev, 
	kvm@...r.kernel.org, iommu@...ts.linux.dev, linux-kernel@...r.kernel.org, 
	Sairaj Kodilkar <sarunkod@....com>, Vasant Hegde <vasant.hegde@....com>, 
	Maxim Levitsky <mlevitsk@...hat.com>, Joao Martins <joao.m.martins@...cle.com>, 
	Francesco Lavra <francescolavra.fl@...il.com>, David Matlack <dmatlack@...gle.com>
Subject: Re: [PATCH v3 18/62] KVM: SVM: Disable (x2)AVIC IPI virtualization if
 CPU has erratum #1235

On Mon, Jun 23, 2025, Naveen N Rao wrote:
> On Wed, Jun 11, 2025 at 03:45:21PM -0700, Sean Christopherson wrote:
> > diff --git a/arch/x86/kvm/svm/avic.c b/arch/x86/kvm/svm/avic.c
> > index 48c737e1200a..bf8b59556373 100644
> > --- a/arch/x86/kvm/svm/avic.c
> > +++ b/arch/x86/kvm/svm/avic.c
> > @@ -1187,6 +1187,14 @@ bool avic_hardware_setup(void)
> >  	if (x2avic_enabled)
> >  		pr_info("x2AVIC enabled\n");
> >  
> > +	/*
> > +	 * Disable IPI virtualization for AMD Family 17h CPUs (Zen1 and Zen2)
> > +	 * due to erratum 1235, which results in missed GA log events and thus
> 							^^^^^^^^^^^^^
> Not sure I understand the reference to GA log events here -- those are 
> only for device interrupts and not IPIs.

Doh, you're absolutely right.  I'll fix to this when applying:

	/*
	 * Disable IPI virtualization for AMD Family 17h CPUs (Zen1 and Zen2)
	 * due to erratum 1235, which results in missed VM-Exits on the sender
	 * and thus missed wake events for blocking vCPUs due to the CPU
	 * failing to see a software update to clear IsRunning.
	 */