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

[Roger Pau Monné <roger.pau@xxxxxxxxxx>]

On Mon, Jul 02, 2018 at 10:57:26AM +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>

Reviewed-by: Roger Pau Monné <roger.pau@xxxxxxxxxx>

> ---
> CC: Jan Beulich <JBeulich@xxxxxxxx>
> CC: Wei Liu <wei.liu2@xxxxxxxxxx>
> CC: Roger Pau Monné <roger.pau@xxxxxxxxxx>
> CC: Sergey Dyasli <sergey.dyasli@xxxxxxxxxx>
> ---
>  xen/arch/x86/cpu/common.c |  1 -
>  xen/arch/x86/msr.c        | 30 +-----------------------------
>  xen/include/asm-x86/msr.h |  2 --
>  3 files changed, 1 insertion(+), 32 deletions(-)
> 
> diff --git a/xen/arch/x86/cpu/common.c b/xen/arch/x86/cpu/common.c
> index 3548b12..b9ff6f8 100644
> --- a/xen/arch/x86/cpu/common.c
> +++ b/xen/arch/x86/cpu/common.c
> @@ -119,7 +119,6 @@ bool __init probe_cpuid_faulting(void)
>       {
>               struct msr_domain_policy *dp = &raw_msr_domain_policy;
>  
> -             dp->plaform_info.available = true;
>               if (val & MSR_PLATFORM_INFO_CPUID_FAULTING)
>                       dp->plaform_info.cpuid_faulting = true;

To reduce code size:

dp->plaform_info.cpuid_faulting = val & MSR_PLATFORM_INFO_CPUID_FAULTING;

Roger.

_______________________________________________
Xen-devel mailing list
Xen-devel@xxxxxxxxxxxxxxxxxxxx
https://lists.xenproject.org/mailman/listinfo/xen-devel