linux-kernel - Re: [PATCH V6 2/5] perf/x86/kvm: Avoid unnecessary work in guest filtering

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Date:   Mon, 4 Feb 2019 10:57:32 -0500
From:   "Liang, Kan" <kan.liang@...ux.intel.com>
To:     Peter Zijlstra <peterz@...radead.org>
Cc:     x86@...nel.org, linux-kernel@...r.kernel.org, tglx@...utronix.de,
        bp@...en8.de, mingo@...hat.com, ak@...ux.intel.com,
        eranian@...gle.com
Subject: Re: [PATCH V6 2/5] perf/x86/kvm: Avoid unnecessary work in guest
 filtering



On 2/4/2019 10:44 AM, Peter Zijlstra wrote:
> On Mon, Feb 04, 2019 at 04:38:27PM +0100, Peter Zijlstra wrote:
>> +static const struct x86_cpu_desc isolation_ucodes[] = {
>> +	INTEL_CPU_DESC(INTEL_FAM6_KABYLAKE_MOBILE,	 9, 0x0000004e),
>> +	INTEL_CPU_DESC(INTEL_FAM6_KABYLAKE_MOBILE,	10, 0x0000004e),
>> +	INTEL_CPU_DESC(INTEL_FAM6_KABYLAKE_MOBILE,	11, 0x0000004e),
>> +	INTEL_CPU_DESC(INTEL_FAM6_KABYLAKE_MOBILE,	12, 0x0000004e),
> 
>> +	INTEL_CPU_DESC(INTEL_FAM6_KABYLAKE_DESKTOP,	10, 0x0000004e),
>> +	INTEL_CPU_DESC(INTEL_FAM6_KABYLAKE_DESKTOP,	11, 0x0000004e),
>> +	INTEL_CPU_DESC(INTEL_FAM6_KABYLAKE_DESKTOP,	12, 0x0000004e),
>> +	INTEL_CPU_DESC(INTEL_FAM6_KABYLAKE_DESKTOP,	13, 0x0000004e),
> 
> Do we want a special stepping (0 / -1) to be able to denote 'all' ?
> 

Something like as below?
#define X86_STEPPING_ANY	0xff

As my understanding, the microcode version for each stepping is 
independent and irrelevant. The 0x0000004e should be just coincidence.
If so, I don't think X86_STEPPING_ANY is very useful.

Andi, if I'm wrong please correct me.

Thanks,
Kan