linux-kernel - Re: [PATCH] KVM: SVM: Check vCPU ID against max x2AVIC ID if and only if x2AVIC is enabled

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Message-ID: <aWfOY7v3T_SRdHMp@blrnaveerao1>
Date: Wed, 14 Jan 2026 23:05:54 +0530
From: Naveen N Rao <naveen@...nel.org>
To: Sean Christopherson <seanjc@...gle.com>
Cc: Paolo Bonzini <pbonzini@...hat.com>, kvm@...r.kernel.org, 
	linux-kernel@...r.kernel.org, Suravee Suthikulpanit <suravee.suthikulpanit@....com>
Subject: Re: [PATCH] KVM: SVM: Check vCPU ID against max x2AVIC ID if and
 only if x2AVIC is enabled

On Mon, Jan 12, 2026 at 03:28:05PM -0800, Sean Christopherson wrote:
> When allocating the AVIC backing page, only check one of the max AVIC vs.
> x2AVIC ID based on whether or not x2AVIC is enabled.  Doing so fixes a bug
> where KVM incorrectly inhibits AVIC if x2AVIC is _disabled_ and any vCPU
> with a non-zero APIC ID is created, as x2avic_max_physical_id is left '0'
> when x2AVIC is disabled.
> 
> Fixes: 940fc47cfb0d ("KVM: SVM: Add AVIC support for 4k vCPUs in x2AVIC mode")
> Cc: stable@...r.kernel.org
> Cc: Naveen N Rao (AMD) <naveen@...nel.org>
> Cc: Suravee Suthikulpanit <suravee.suthikulpanit@....com>
> Signed-off-by: Sean Christopherson <seanjc@...gle.com>
> ---
>  arch/x86/kvm/svm/avic.c | 4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)

I think the bad commit is:
f628a34a9d52 ("KVM: SVM: Replace "avic_mode" enum with "x2avic_enabled" boolean")

... which introduced x2avic_enabled.

Other than that:
Reviewed-by: Naveen N Rao (AMD) <naveen@...nel.org>


Thanks,
Naveen