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

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Message-ID: <20090830114329.GA9038@liondog.tnic>
Date:	Sun, 30 Aug 2009 13:43:30 +0200
From:	Borislav Petkov <petkovbb@...glemail.com>
To:	"H. Peter Anvin" <hpa@...or.com>
Cc:	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 Mon, Aug 24, 2009 at 11:44:30PM -0700, H. Peter Anvin wrote:
> 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.

Ok, here's what I could come up with. It seems to work (tested only on a
Fam10h box), it should cover all our msr needs for now and alleviate the
need for adding yet another paravirt_ops member.

-- 
Regards/Gruss,
    Boris.
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