Re: [Xen-devel] [PATCH v2 09/30] xen/x86: Store antifeatures inverted in a featureset

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> On 05.02.16 at 14:42, <andrew.cooper3@xxxxxxxxxx> wrote:
> Awkwardly, some new feature bits mean "Feature $X no longer works".
> Store these inverted in a featureset.
> 
> This permits safe zero-extending of a smaller featureset as part of a
> comparison, and safe reasoning (subset?, superset?, compatible? etc.)
> without specific knowldge of meaning of each bit.
> 
> Signed-off-by: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>

Acked-by: Jan Beulich <JBeulich@xxxxxxxx>
albeit ...

> @@ -158,7 +174,7 @@
>  #define X86_FEATURE_INVPCID       ( 5*32+10) /*   Invalidate Process Context 
> ID */
>  #define X86_FEATURE_RTM           ( 5*32+11) /*   Restricted Transactional 
> Memory */
>  #define X86_FEATURE_CMT           ( 5*32+12) /*   Cache Monitoring 
> Technology */
> -#define X86_FEATURE_NO_FPU_SEL    ( 5*32+13) /*   FPU CS/DS stored as zero */
> +#define X86_FEATURE_FPU_SEL       ( 5*32+13) /*!  FPU CS/DS stored as zero */

... changes like this to the public interface should normally be
avoided (i.e. you had better left out the "NO" one when you first
created this file).

Jan


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