Re: [Xen-devel] [PATCH v2 1/2] x86/hvm: allow guest to use clflushopt and clwb

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> On 30.12.15 at 12:48, <haozhong.zhang@xxxxxxxxx> wrote:
> --- a/xen/arch/x86/hvm/hvm.c
> +++ b/xen/arch/x86/hvm/hvm.c
> @@ -4583,21 +4583,30 @@ void hvm_cpuid(unsigned int input, unsigned int *eax, 
> unsigned int *ebx,
>              *edx &= ~cpufeat_mask(X86_FEATURE_PSE36);
>          break;
>      case 0x7:
> -        if ( (count == 0) && !cpu_has_smep )
> -            *ebx &= ~cpufeat_mask(X86_FEATURE_SMEP);
> +        if ( count == 0 )
> +        {
> +            if ( !cpu_has_smep )
> +                *ebx &= ~cpufeat_mask(X86_FEATURE_SMEP);
> +
> +            if ( !cpu_has_smap )
> +                *ebx &= ~cpufeat_mask(X86_FEATURE_SMAP);
> +
> +            /* Don't expose MPX to hvm when VMX support is not available */
> +            if ( !(vmx_vmexit_control & VM_EXIT_CLEAR_BNDCFGS) ||
> +                 !(vmx_vmentry_control & VM_ENTRY_LOAD_BNDCFGS) )
> +                *ebx &= ~cpufeat_mask(X86_FEATURE_MPX);
>  
> -        if ( (count == 0) && !cpu_has_smap )
> -            *ebx &= ~cpufeat_mask(X86_FEATURE_SMAP);
> +            /* Don't expose INVPCID to non-hap hvm. */
> +            if ( !hap_enabled(d) )
> +                *ebx &= ~cpufeat_mask(X86_FEATURE_INVPCID);
>  
> -        /* Don't expose MPX to hvm when VMX support is not available */
> -        if ( (count == 0) &&
> -             (!(vmx_vmexit_control & VM_EXIT_CLEAR_BNDCFGS) ||
> -              !(vmx_vmentry_control & VM_ENTRY_LOAD_BNDCFGS)) )
> -            *ebx &= ~cpufeat_mask(X86_FEATURE_MPX);
> +            if ( !cpu_has_clflushopt )
> +                *ebx &= ~cpufeat_mask(X86_FEATURE_CLFLUSHOPT);
> +
> +            if ( !cpu_has_clwb )
> +                *ebx &= ~cpufeat_mask(X86_FEATURE_CLWB);

I don't think we need this: Other than other things adjusted here,
there's nothing disabling these two features when found available,
and there are no extra conditions to consider. Otherwise, if we
were to follow this route, quite a bit of code would need to be
added to other case statements in this function. But that's all (I
think) going to be taken care of by Andrew's CPUID leveling series.

Jan


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