Re: [Xen-devel] [PATCH RFC 01/31] xen/public: Export featureset information in the public API

[Andrew Cooper <andrew.cooper3@xxxxxxxxxx>]

On 22/12/15 16:28, Jan Beulich wrote:
>>>> On 16.12.15 at 22:24, <andrew.cooper3@xxxxxxxxxx> wrote:
>> +/* VIA/Cyrix/Centaur-defined CPU features, CPUID level 0xC0000001, FSMAX+2 
>> */
>> +#define X86_FEATURE_XSTORE  ((FSMAX+1)*32+ 2) /* on-CPU RNG present (xstore 
>> insn) */
>> +#define X86_FEATURE_XSTORE_EN       ((FSMAX+1)*32+ 3) /* on-CPU RNG enabled 
>> */
>> +#define X86_FEATURE_XCRYPT  ((FSMAX+1)*32+ 6) /* on-CPU crypto (xcrypt 
>> insn) */
>> +#define X86_FEATURE_XCRYPT_EN       ((FSMAX+1)*32+ 7) /* on-CPU crypto 
>> enabled */
>> +#define X86_FEATURE_ACE2    ((FSMAX+1)*32+ 8) /* Advanced Cryptography 
>> Engine v2 */
>> +#define X86_FEATURE_ACE2_EN ((FSMAX+1)*32+ 9) /* ACE v2 enabled */
>> +#define X86_FEATURE_PHE             ((FSMAX+1)*32+10) /* PadLock Hash 
>> Engine */
>> +#define X86_FEATURE_PHE_EN  ((FSMAX+1)*32+11) /* PHE enabled */
>> +#define X86_FEATURE_PMM             ((FSMAX+1)*32+12) /* PadLock Montgomery 
>> Multiplier */
>> +#define X86_FEATURE_PMM_EN  ((FSMAX+1)*32+13) /* PMM enabled */
> None of these get consumed anywhere - if you already touch this
> code, just drop all of them.

X86_FEATURE_XSTORE gets used in xen/arch/x86/cpu/centaur.c to stash word
0xC0000001, but nothing actually reads the stashed values.

I could do a precursor patch which drops the stashing of this
information, which will result in NCAPINTS getting shorter by the end of
the series.

>
>> +/*
>> + * CPUID leaf shorthand:
>> + * - optional 'e', Extended (0x8xxxxxxx)
>> + * - leaf, uppercase hex
>> + * - register, lowercase
>> + * - optional subleaf, uppercase hex
>> + */
>> +#define XEN_FEATURESET_1d     0 /* 0x00000001.edx      */
>> +#define XEN_FEATURESET_1c     1 /* 0x00000001.ecx      */
>> +#define XEN_FEATURESET_e1d    2 /* 0x80000001.edx      */
>> +#define XEN_FEATURESET_e1c    3 /* 0x80000001.ecx      */
>> +#define XEN_FEATURESET_Da1    4 /* 0x0000000d:1.eax    */
>> +#define XEN_FEATURESET_7b0    5 /* 0x00000007:0.ebx    */
> This ends up being pretty cryptic.

Perhaps at a first glance, but there are so many uses that a shorthand
really is needed.  See especially the MSR masking patches towards the
end of the series.

>
>> +#define XEN_NR_FEATURESET_ENTRIES (XEN_FEATURESET_7b0 + 1)
> This shouldn't be exposed, as it will necessarily change sooner or later.

Hmm yes - I think I can alter where this lives, although libxc does need
to be able to get this value.

~Andrew

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