Re: [PATCH v10 5/7] x86/cpufeature: Detect CPUID faulting support

[Borislav Petkov]

On Tue, Nov 08, 2016 at 10:39:54AM -0800, Kyle Huey wrote:
> Intel supports faulting on the CPUID instruction beginning with Ivy Bridge.
> When enabled, the processor will fault on attempts to execute the CPUID
> instruction with CPL>0. This will allow a ptracer to emulate the CPUID
> instruction.
> 
> Bit 31 of MSR_PLATFORM_INFO advertises support for this feature. It is
> documented in detail in Section 2.3.2 of
> http://www.intel.com/content/dam/www/public/us/en/documents/application-notes/virtualization-technology-flexmigration-application-note.pdf
> 
> Detect support for this feature and expose it as X86_FEATURE_CPUID_FAULT.
> 
> Signed-off-by: Kyle Huey <kh...@kylehuey.com>
> Reviewed-by: Andy Lutomirski <l...@kernel.org>
> ---
>  arch/x86/include/asm/cpufeatures.h |  1 +
>  arch/x86/include/asm/msr-index.h   |  2 ++
>  arch/x86/kernel/cpu/scattered.c    | 22 +++++++++++++++++++++-
>  3 files changed, 24 insertions(+), 1 deletion(-)
> 
> diff --git a/arch/x86/include/asm/cpufeatures.h 
> b/arch/x86/include/asm/cpufeatures.h
> index a396292..62962e8 100644
> --- a/arch/x86/include/asm/cpufeatures.h
> +++ b/arch/x86/include/asm/cpufeatures.h
> @@ -184,16 +184,17 @@
>   * Auxiliary flags: Linux defined - For features scattered in various
>   * CPUID levels like 0x6, 0xA etc, word 7.
>   *
>   * Reuse free bits when adding new feature flags!
>   */
>  
>  #define X86_FEATURE_CPB              ( 7*32+ 2) /* AMD Core Performance 
> Boost */
>  #define X86_FEATURE_EPB              ( 7*32+ 3) /* IA32_ENERGY_PERF_BIAS 
> support */
> +#define X86_FEATURE_CPUID_FAULT ( 7*32+ 4) /* Intel CPUID faulting */

Bit 0 in that leaf is free. Also, bit 4 is already claimed by RDT/CAT/...
whatever that thing is going to be called so please do:

#define X86_FEATURE_CPUID_FAULT ( 7*32+ 0) /* Intel CPUID faulting */

>  
>  #define X86_FEATURE_HW_PSTATE        ( 7*32+ 8) /* AMD HW-PState */
>  #define X86_FEATURE_PROC_FEEDBACK ( 7*32+ 9) /* AMD ProcFeedbackInterface */
>  
>  #define X86_FEATURE_INTEL_PT ( 7*32+15) /* Intel Processor Trace */
>  #define X86_FEATURE_AVX512_4VNNIW (7*32+16) /* AVX-512 Neural Network 
> Instructions */
>  #define X86_FEATURE_AVX512_4FMAPS (7*32+17) /* AVX-512 Multiply Accumulation 
> Single precision */

...

>       for (cb = cpuid_bits; cb->feature; cb++) {
>  
>               /* Verify that the level is valid */
>               max_level = cpuid_eax(cb->level & 0xffff0000);
>               if (max_level < cb->level ||
>                   max_level > (cb->level | 0xffff))
>                       continue;
>  
>               cpuid_count(cb->level, cb->sub_leaf, &regs[CR_EAX],
>                           &regs[CR_EBX], &regs[CR_ECX], &regs[CR_EDX]);
>  
>               if (regs[cb->reg] & (1 << cb->bit))
>                       set_cpu_cap(c, cb->feature);
>       }
> +
> +     for (mb = msr_bits; mb->feature; mb++) {
> +             if (rdmsrl_safe(mb->msr, &msrval))
> +                     continue;

<--- newline here.

> +             if (msrval & (1ULL << mb->bit))

                if (msrval & BIT_ULL(mb->bit))


> +                     set_cpu_cap(c, mb->feature);
> +     }
>  }
> -- 

-- 
Regards/Gruss,
    Boris.

SUSE Linux GmbH, GF: Felix Imendörffer, Jane Smithard, Graham Norton, HRB 21284 
(AG Nürnberg)
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