linux-kernel - Re: [git-pull -tip] x86: Addition of cpufeatures to friendly access miscellaneous MSRs

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Message-ID: <20090511184727.GF10722@erda.amd.com>
Date:	Mon, 11 May 2009 20:47:28 +0200
From:	Robert Richter <robert.richter@....com>
To:	"H. Peter Anvin" <hpa@...or.com>
CC:	Jaswinder Singh Rajput <jaswinder@...nel.org>,
	Ingo Molnar <mingo@...e.hu>, "H. Peter Anvin" <hpa@...nel.org>,
	x86 maintainers <x86@...nel.org>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: [git-pull -tip] x86: Addition of cpufeatures to friendly
	access miscellaneous MSRs

On 11.05.09 11:15:52, H. Peter Anvin wrote:
> Jaswinder Singh Rajput wrote:
>> Jaswinder Singh Rajput (15):
>>       x86: Add cpufeature for Processor Name
>>       x86: Add cpufeatures for Advanced Power Management
>>       x86: Add cpufeature for Microcode update
>>       x86: Add cpufeature for Cache MSRs
>>       x86: Add cpufeature for Hard and Soft Poweron configuration
>>       x86: Add cpufeature for Scaleable bus speed
>>       x86: Add cpufeature for Miscellaneous Features
>>       x86: Add cpufeature for Platform feature
>>       x86: Add cpufeature for Hardware configuration
>>       x86: Add cpufeature for System configuration
>>       x86: Add cpufeature for System management mode (SMM)
>>       x86: Add cpufeature for MM configuration
>>       x86: Add cpufeature for Bus configuration
>>       x86: Add cpufeature for performance frequency APERF/MPERF
>>       x86: Add cpufeature for ancient performance monitoring
>
> Overall, I'm rather confused what the point of this is supposed to be. 
> There is value to centralizing CPU knowledge, but some of these flags are 
> only used in one place, and as far as I can see in several of your patches 
> they aren't used *at all*.
>
> If there is no in-kernel user there is absolutely no point to this.

>From the pull request subject

 x86: Addition of cpufeatures to friendly access miscellaneous MSRs

I assume this is mainly done for dumping msrs for debugging
purposes. I don't want to start the discussion again if this really
should be done in kernel space. I would rather parse and decode msr
registers in userspace. MSR tables could be easily implemented there.

Anyway, I think this was already decided. So, maybe for debugging we
should simply read the msrs with rdmsr_safe() and use the exception
handler to check if the msr is implemented. This would avoid most of
the otherwise unused cpufeature flags above.

-Robert

-- 
Advanced Micro Devices, Inc.
Operating System Research Center
email: robert.richter@....com

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