linux-kernel - Re: [tip:x86/urgent] x86, AMD: Disable wrongly set X86_FEATURE_LAHF

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Message-ID: <4A93884E.3000403@zytor.com>
Date:	Mon, 24 Aug 2009 23:44:30 -0700
From:	"H. Peter Anvin" <hpa@...or.com>
To:	Borislav Petkov <petkovbb@...glemail.com>,
	Ingo Molnar <mingo@...e.hu>, mingo@...hat.com,
	linux-kernel@...r.kernel.org, kjwinchester@...il.com,
	tglx@...utronix.de, borislav.petkov@....com,
	linux-tip-commits@...r.kernel.org
Subject: Re: [tip:x86/urgent] x86, AMD: Disable wrongly set X86_FEATURE_LAHF_LM
 CPUID bit

On 08/24/2009 10:52 PM, Borislav Petkov wrote:
> On Mon, Aug 24, 2009 at 01:34:07PM -0700, H. Peter Anvin wrote:
>> Looks reasonable... although part of me wonders if having a pointer to
>> an array containing the entire register file in and out is even better,
>> of if I'm just overengineering at this point.
> 
> Hmm, let's have necessity determine that. I can only think of %edi being
> used as an input reg to rd/wrmsr beside %ecx but it could be very well
> that some other x86 hardware uses other regs too. Do we actually need
> all regs or a two should suffice?
> 

Hard to know.  In theory we shouldn't need ESI and EDI either!

As I said, I wouldn't have worried about it at all if it wasn't for
paravirt_ops turning these things into ABIs.

	-hpa

-- 
H. Peter Anvin, Intel Open Source Technology Center
I work for Intel.  I don't speak on their behalf.

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