From mboxrd@z Thu Jan  1 00:00:00 1970
From: Andrew Cooper <andrew.cooper3@citrix.com>
Subject: Re: [PATCH v2 09/30] xen/x86: Store antifeatures
 inverted in a featureset
Date: Fri, 12 Feb 2016 16:50:18 +0000
Message-ID: <56BE0D4A.4030001@citrix.com>
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To: Jan Beulich <JBeulich@suse.com>
Cc: Xen-devel <xen-devel@lists.xen.org>
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On 12/02/16 16:47, Jan Beulich wrote:
>>>> On 05.02.16 at 14:42, <andrew.cooper3@citrix.com> 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@citrix.com>
> Acked-by: Jan Beulich <JBeulich@suse.com>
> 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).

I couldn't find a neater way of doing this while keeping the name
consistent with its representation.  I took the decision that this is
the lesser of the available evils when making this change.

I am open to alternate suggestions.

~Andrew