Re: [PATCH 4/4] amd/virt_ssbd: add to max HVM policy when SSB_NO is available

[Jan Beulich <jbeulich@xxxxxxxx>]

On 11.10.2022 18:02, Roger Pau Monne wrote:
> --- a/xen/arch/x86/cpu/amd.c
> +++ b/xen/arch/x86/cpu/amd.c
> @@ -814,7 +814,9 @@ void amd_set_ssbd(bool enable)
>               wrmsr(MSR_VIRT_SPEC_CTRL, enable ? SPEC_CTRL_SSBD : 0, 0);
>       else if ( amd_legacy_ssbd )
>               core_set_legacy_ssbd(enable);
> -     else
> +     else if ( cpu_has_ssb_no ) {

Nit: While already an issue in patch 1, it is actually the combination
of inner blanks and brace placement which made me spot the style issue
here.

> +             /* Nothing to do. */

How is the late placement here in line with ...

> --- a/xen/arch/x86/cpuid.c
> +++ b/xen/arch/x86/cpuid.c
> @@ -558,11 +558,16 @@ static void __init calculate_hvm_max_policy(void)
>          __clear_bit(X86_FEATURE_IBRSB, hvm_featureset);
>          __clear_bit(X86_FEATURE_IBRS, hvm_featureset);
>      }
> -    else if ( boot_cpu_has(X86_FEATURE_AMD_SSBD) )
> +    else if ( boot_cpu_has(X86_FEATURE_AMD_SSBD) ||
> +              boot_cpu_has(X86_FEATURE_SSB_NO) )
>          /*
>           * If SPEC_CTRL.SSBD is available VIRT_SPEC_CTRL.SSBD can be exposed
>           * and implemented using the former. Expose in the max policy only as
>           * the preference is for guests to use SPEC_CTRL.SSBD if available.
> +         *
> +         * Allow VIRT_SSBD in the max policy if SSB_NO is exposed for 
> migration
> +         * compatibility reasons.  If SSB_NO is present setting
> +         * VIRT_SPEC_CTRL.SSBD is a no-op.
>           */
>          __set_bit(X86_FEATURE_VIRT_SSBD, hvm_featureset);

... this comment addition talking about "no-op"?

Jan