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

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Message-ID: <f67d228e-c65d-479c-30ec-ee532833d8f9@linux.intel.com>
Date:   Mon, 4 Feb 2019 11:23:13 -0500
From:   "Liang, Kan" <kan.liang@...ux.intel.com>
To:     Borislav Petkov <bp@...en8.de>
Cc:     Peter Zijlstra <peterz@...radead.org>, x86@...nel.org,
        linux-kernel@...r.kernel.org, tglx@...utronix.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 11:04 AM, Borislav Petkov wrote:
> On Mon, Feb 04, 2019 at 10:57:32AM -0500, Liang, Kan wrote:
>>
>>
>> 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.
> 
> Huh?
> 
> Why are we looking at the stepping then?
> 
> x86_match_cpu_with_stepping() <---
> 

I mean that the microcode version number is irrelevant between stepping.
Let's use SKL server as an example.
+	INTEL_CPU_DESC(INTEL_FAM6_SKYLAKE_X,		 3, 0x00000021),
+	INTEL_CPU_DESC(INTEL_FAM6_SKYLAKE_X,		 4, 0x00000000),

We need the function to check the min microcode version number for each 
stepping.


Thanks,
Kan