Re: [PATCH RFC v1 07/20] KVM: nVMX: Support the extended instruction info field

[Chang S. Bae]

On 11/11/2025 9:48 AM, Paolo Bonzini wrote:
> but here you must not check XCR0, the extended instruction information 
> field is always available.  The spec says "A non-Intel® APX enabled VMM 
> is free to continue using the legacy definition of the field, since lack 
> of Intel® APX enabling will guarantee that regIDs are only 4-bits, 
> maximum" but you can also use the extended instruction information field 
> if you want.  So, I'd make this also static_cpu_has(X86_FEATURE_APX).

I just got confirmation from the hardware folks. The CPUID enumeration 
alone is sufficient to indicate the presence and usability of the 
extended instruction information field, regardless of the XCR0 state.