linux-kernel - Re: [PATCH v2] x86, msr: Document AMD "tweak MSRs", use MSR_FnnH

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Message-ID: <a247e792-f7fc-84d6-bd5c-66116ee55d88@redhat.com>
Date:   Tue, 25 Apr 2017 18:48:47 +0200
From:   Denys Vlasenko <dvlasenk@...hat.com>
To:     Borislav Petkov <bp@...en8.de>
Cc:     Ingo Molnar <mingo@...hat.com>, Andy Lutomirski <luto@...nel.org>,
        Brian Gerst <brgerst@...il.com>,
        Peter Zijlstra <peterz@...radead.org>,
        "H. Peter Anvin" <hpa@...ux.intel.com>, x86@...nel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2] x86, msr: Document AMD "tweak MSRs", use MSR_FnnH_NAME
 scheme for them

On 04/25/2017 06:23 PM, Borislav Petkov wrote:
> On Tue, Apr 25, 2017 at 06:15:23PM +0200, Denys Vlasenko wrote:
>> On 04/25/2017 06:06 PM, Borislav Petkov wrote:
>>> Pls no. Not every MSR for every family. Only the 4 which are actually
>>> being used. We can't hold in here the full 32-bit MSR space.
>>
>> The replacement of four define names is not the purpose
>> of the proposed patch.
>>
>> The patch was prompted by the realization that these particular MSRs
>> are so badly and inconsistently documented that it takes many hours
>> of work and requires reading of literally a dozen PDFs to figure out
>> what are their names, which CPUs have them, and what bits are known.
>
> They're all documented in the respective BKDGs or revision guides.

Yes. For some definition of "documented".

Let's say you are looking at all available documentation for Fam10h CPUs -
BKDG, Revision Guide, five volumes of APM, software optimization guide.
Eight documents.

If you read all of them, you can find exactly one mention that
MSR 0xC0011029 exists. It is mentioned by number.

As a reader of this documentation, can you find out what is it?
Does it have a name, at least?

You are right that kernel is not exactly the best place to store more info
about such things, but AMD probably won't accept my edits to their
documentation.