Re: [RFC PATCH v2 1/5] KVM: SVM: Stop warning if x2AVIC feature bit alone is enabled

[Sean Christopherson <seanjc@google.com>]

On Thu, Sep 04, 2025, Naveen N Rao (AMD) wrote:
> A platform can choose to disable AVIC by turning off the AVIC CPUID
> feature bit, while keeping x2AVIC CPUID feature bit enabled to indicate
> AVIC support for the x2APIC MSR interface. Since this is a valid
> configuration, stop printing a warning.
> 
> Signed-off-by: Naveen N Rao (AMD) <naveen@kernel.org>
> ---
>  arch/x86/kvm/svm/avic.c | 8 +-------
>  1 file changed, 1 insertion(+), 7 deletions(-)
> 
> diff --git a/arch/x86/kvm/svm/avic.c b/arch/x86/kvm/svm/avic.c
> index a34c5c3b164e..346cd23a43a9 100644
> --- a/arch/x86/kvm/svm/avic.c
> +++ b/arch/x86/kvm/svm/avic.c
> @@ -1101,14 +1101,8 @@ bool avic_hardware_setup(void)
>  	if (!npt_enabled)
>  		return false;
>  
> -	/* AVIC is a prerequisite for x2AVIC. */
> -	if (!boot_cpu_has(X86_FEATURE_AVIC) && !force_avic) {
> -		if (boot_cpu_has(X86_FEATURE_X2AVIC)) {
> -			pr_warn(FW_BUG "Cannot support x2AVIC due to AVIC is disabled");
> -			pr_warn(FW_BUG "Try enable AVIC using force_avic option");

I agree with the existing code, KVM should treat this as a firmware bug, where
"firmware" could also be the host VMM.  AIUI, x2AVIC can't actualy work without
AVIC support, so enumerating x2AVIC without AVIC is pointless and unexpected.

> -		}
> +	if (!boot_cpu_has(X86_FEATURE_AVIC) && !force_avic)
>  		return false;
> -	}
>  
>  	if (cc_platform_has(CC_ATTR_HOST_SEV_SNP) &&
>  	    !boot_cpu_has(X86_FEATURE_HV_INUSE_WR_ALLOWED)) {
> -- 
> 2.50.1
>