Re: [PATCH v3] x86/cpu/amd: Enable the fixed Instructions Retired counter IRPERF

[Kim Phillips]

Hi Borislav,

On 2/18/20 5:20 AM, Borislav Petkov wrote:
> On Fri, Feb 14, 2020 at 02:18:05PM -0600, Kim Phillips wrote:
>> diff --git a/arch/x86/include/asm/cpufeatures.h b/arch/x86/include/asm/cpufeatures.h
>> index f3327cb56edf..8979d6fcc79c 100644
>> --- a/arch/x86/include/asm/cpufeatures.h
>> +++ b/arch/x86/include/asm/cpufeatures.h
>> @@ -404,5 +404,6 @@
>>  #define X86_BUG_SWAPGS			X86_BUG(21) /* CPU is affected by speculation through SWAPGS */
>>  #define X86_BUG_TAA			X86_BUG(22) /* CPU is affected by TSX Async Abort(TAA) */
>>  #define X86_BUG_ITLB_MULTIHIT		X86_BUG(23) /* CPU may incur MCE during certain page attribute changes */
>> +#define X86_BUG_IRPERF			X86_BUG(24) /* CPU is affected by Instructions Retired counter Erratum 1054 */
> 
> Do you need this bug flag at all?
> 
> If the only reason for its existence is to check it before setting
> the MSR bit enabling IRPERF, then you don't need it. Or is there any
> particular reason why it should show in /proc/cpuinfo?
> 
> IOW, does this work too?

Yes, that works quite nicely, and saves us a bug bit.

The only reason to have it show in /proc/cpuinfo is for userspace,
but they can check for a nonzero count prior to using, instead.

Let me know if you'd like me to send a v4, or if you will just apply
this version of yours.

Thanks,

Kim