Re: [PATCH v4 18/21] KVM: x86: Expose APX foundation feature to guests

[Sean Christopherson]

On Tue, May 12, 2026, Chang S. Bae wrote:
> Add the APX xfeature bit to the list of supported XCR0 components and
> expose the APX feature to guests. Update the maximum supported CPUID leaf
> to 0x29 to include the APX leaf.

Almost forgot.  For the shortlog+change of this patch and the next, the changes
don't expose APX to the guest, they advertise support for APX to host userspace.

This patch also adds support in KVM by allowing XFEATURE_MASK_APX, though I
would argue that belongs in a separate patch anyways.

But the next patch is a pure "advertise to userspace", e.g. a VMM could enumerate
and expose APX_NCI_NDD_NF to a guest with or without the patch.