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

Naveen N Rao
2026-01-14T17:34:42Z

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@vger.kernel.org
> Cc: Naveen N Rao (AMD) <naveen@kernel.org>
> Cc: Suravee Suthikulpanit <suravee.suthikulpanit@amd.com>
> Signed-off-by: Sean Christopherson <seanjc@google.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@kernel.org>

Thanks,
Naveen