Re: [Xen-devel] [PATCH] x86/cpuid: Fix handling of the CPUID.7[0].eax levelling MSR

[Jan Beulich <jbeulich@xxxxxxxx>]

On 09.09.2019 17:51, Andrew Cooper wrote:
> --- a/xen/arch/x86/domctl.c
> +++ b/xen/arch/x86/domctl.c
> @@ -218,11 +218,16 @@ static int update_domain_cpuid_info(struct domain *d,
>          if ( is_pv_domain(d) && ((levelling_caps & LCAP_7ab0) == LCAP_7ab0) )
>          {
>              uint64_t mask = cpuidmask_defaults._7ab0;
> -            uint32_t eax = ctl->eax;
> -            uint32_t ebx = p->feat._7b0;
>  
> -            if ( boot_cpu_data.x86_vendor & (X86_VENDOR_AMD | 
> X86_VENDOR_HYGON) )
> -                mask &= ((uint64_t)eax << 32) | ebx;
> +            /*
> +             * Leaf 7[0].eax is max_subleaf, not a feature mask.  Take it
> +             * wholesale from the policy, but clamp the features in 7[0].ebx
> +             * per usual.
> +             */
> +            if ( boot_cpu_data.x86_vendor &
> +                 (X86_VENDOR_AMD | X86_VENDOR_HYGON) )
> +                mask = (((uint64_t)p->feat.max_subleaf << 32) |
> +                        ((uint32_t)mask | p->feat._7b0));

Assuming you mean & instead of | here, with it fixed
Reviewed-by: Jan Beulich <jbeulich@xxxxxxxx>
Otherwise I'm afraid I don't understand, and need further
explanation.

Jan

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