Re: [RFC PATCH v2 5/5] KVM: SVM: Enable AVIC by default from Zen 4

[Sean Christopherson <seanjc@google.com>]

On Thu, Sep 04, 2025, Naveen N Rao (AMD) wrote:
> +	/* Enable AVIC by default from Zen 4 */
> +	if (default_avic)
> +		avic = boot_cpu_data.x86 > 0x19 || cpu_feature_enabled(X86_FEATURE_ZEN4);

Got distracted and forgot to respond the actual code.  This needs a comment,
because intuitively I expected Zen4 to be inclusive of Zen5 and beyond, i.e. the
model check confused me.  But the kernel's ZenX flags are one-off things.

I also think we should enabled AVIC by default if and only if x2AVIC is supported,
because Zen4+ should all have x2AVIC, and I don't want to incorrectly suggest that
AVIC is fully enabled when in fact the only aspect of AVIC that would be utilized
is KVM's use of the doorbell to deliver interrupts.

> +
>  	if (!avic || !npt_enabled)
>  		goto out;
>