linux-kernel - Re: [PATCH] KVM: SVM: Fix an off-by-one typo in the comment for enabling AVIC by default

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Message-ID: <aV_kLHFQzu7taPS_@google.com>
Date: Thu, 8 Jan 2026 09:06:52 -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
Subject: Re: [PATCH] KVM: SVM: Fix an off-by-one typo in the comment for
 enabling AVIC by default

On Thu, Jan 08, 2026, Naveen N Rao wrote:
> On Wed, Jan 07, 2026 at 12:45:46PM -0800, Sean Christopherson wrote:
> > Fix a goof in the comment that documents KVM's logic for enabling AVIC by
> > default to reference Zen5+ as family 0x1A (Zen5), not family 0x19 (Zen4).
> > The code is correct (checks for _greater_ than 0x19), only the comment is
> > flawed.
> 
> I had thought that the comment was correct and that you wanted to 
> reference Zen4 there. That is:
> 	family 0x19 (Zen4) and later (Zen5+),
> 
> Though family 0x19 also includes Zen3 :/
> 
> I think it would be better to update the code as well, just so it is 
> easier to correlate the comment and the code?
> 
>         if (avic == AVIC_AUTO_MODE)
>                 avic = boot_cpu_has(X86_FEATURE_X2AVIC) &&
> -                      (boot_cpu_data.x86 > 0x19 || cpu_feature_enabled(X86_FEATURE_ZEN4));
> +                      (cpu_feature_enabled(X86_FEATURE_ZEN4) || boot_cpu_data.x86 >= 0x1A);

This thought crossed my mind as well.  I'll send a v2 with this, I especially
like the idea of swapping the ordering so that the checks are "ascending".