linux-kernel - Re: [PATCH v3] x86: clear incorrectly forced X86_FEATURE_LAHF

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Message-ID: <20090811155106.GB16173@aftab>
Date:	Tue, 11 Aug 2009 17:51:06 +0200
From:	Borislav Petkov <borislav.petkov@....com>
To:	Mikael Pettersson <mikpe@...uu.se>
CC:	Kevin Winchester <kjwinchester@...il.com>,
	Borislav Petkov <petkovbb@...glemail.com>,
	Ingo Molnar <mingo@...e.hu>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v3] x86: clear incorrectly forced X86_FEATURE_LAHF_LM
 flag

On Tue, Aug 11, 2009 at 04:37:56PM +0200, Mikael Pettersson wrote:
> Since the BIOS apparently wrote some MSR to get LAHF_LM incorrectly
> reported by CPUID, would it be possible to also correct that MSR so
> that applications that execute CPUID get the correct feature flags?

That's a good catch, actually. We have to turn off that bit in the cpuid
leaf too if the CPU doesn't support the instructions so that cpuid info
is consistent. LAHF/SAHF support in 64bit mode has to be cpuid-checked
prior to using them so that info has to be correct.

@Kevin: willing to try a patch or two?

-- 
Regards/Gruss,
Boris.

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