Re: [PATCH 1/2] x86/cpufeatures: Add the Virtual SPEC_CTRL feature

[Jim Mattson]

On Mon, Dec 7, 2020 at 2:38 PM Babu Moger <babu.moger@xxxxxxx> wrote:
>
> Newer AMD processors have a feature to virtualize the use of the SPEC_CTRL
> MSR. This feature is identified via CPUID 0x8000000A_EDX[20]. When present,
> the SPEC_CTRL MSR is automatically virtualized and no longer requires
> hypervisor intervention.
>
> Signed-off-by: Babu Moger <babu.moger@xxxxxxx>
> ---
>  arch/x86/include/asm/cpufeatures.h |    1 +
>  1 file changed, 1 insertion(+)
>
> diff --git a/arch/x86/include/asm/cpufeatures.h b/arch/x86/include/asm/cpufeatures.h
> index dad350d42ecf..d649ac5ed7c7 100644
> --- a/arch/x86/include/asm/cpufeatures.h
> +++ b/arch/x86/include/asm/cpufeatures.h
> @@ -335,6 +335,7 @@
>  #define X86_FEATURE_AVIC               (15*32+13) /* Virtual Interrupt Controller */
>  #define X86_FEATURE_V_VMSAVE_VMLOAD    (15*32+15) /* Virtual VMSAVE VMLOAD */
>  #define X86_FEATURE_VGIF               (15*32+16) /* Virtual GIF */
> +#define X86_FEATURE_V_SPEC_CTRL                (15*32+20) /* Virtual SPEC_CTRL */

Shouldn't this bit be reported by KVM_GET_SUPPORTED_CPUID when it's
enumerated on the host?

>  /* Intel-defined CPU features, CPUID level 0x00000007:0 (ECX), word 16 */
>  #define X86_FEATURE_AVX512VBMI         (16*32+ 1) /* AVX512 Vector Bit Manipulation instructions*/
>