Re: [Xen-devel] [PATCH 2/3] x86/msr: Drop {MISC_ENABLES, PLATFORM_INFO}.available

[Sergey Dyasli <sergey.dyasli@xxxxxxxxxx>]

On Mon, 2018-07-02 at 10:57 +0100, Andrew Cooper wrote:
> These MSRs are non-architectural and the available booleans were used in lieu
> of an architectural signal of availability.  The MSRs are unconditionally
> available to HVM guests, but currently for PV guests, are hidden when CPUID
> faulting is unavailable.
> 
> However, in hindsight, the additional booleans make toolstack MSR interactions
> more complicated.  As the behaviour of the MSRs is reserved when unavailable,
> unconditionally letting the MSRs be accessible is compatible behaviour, even
> for PV guests.
> 
> The new behaviour is:
>   * PLATFORM_INFO is unconditionally readable even for PV guests and will
>     indicate the presense or absense of CPUID Faulting in bit 31.
>   * MISC_FEATURES_ENABLES is uncondtionally readable, and bit 0 may be set iff
>     PLATFORM_INFO reports that CPUID Faulting is available.
> 
> Signed-off-by: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
> ---
> 
> diff --git a/xen/include/asm-x86/msr.h b/xen/include/asm-x86/msr.h
> index afbeb7f..c28371c 100644
> --- a/xen/include/asm-x86/msr.h
> +++ b/xen/include/asm-x86/msr.h
> @@ -262,7 +262,6 @@ struct msr_domain_policy
>  {
>      /* 0x000000ce  MSR_INTEL_PLATFORM_INFO */
>      struct {
> -        bool available; /* This MSR is non-architectural */
>          bool cpuid_faulting;
>      } plaform_info;
>  };
> @@ -290,7 +289,6 @@ struct msr_vcpu_policy
>  
>      /* 0x00000140  MSR_INTEL_MISC_FEATURES_ENABLES */
>      struct {
> -        bool available; /* This MSR is non-architectural */
>          bool cpuid_faulting;
>      } misc_features_enables;
>  };

Could you add comments saying that those 2 MSRs are always available
for all guests?

With that, Reviewed-by: Sergey Dyasli <sergey.dyasli@xxxxxxxxxx>

-- 
Thanks,
Sergey
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