From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753459AbZHMOVY (ORCPT ); Thu, 13 Aug 2009 10:21:24 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1751472AbZHMOVX (ORCPT ); Thu, 13 Aug 2009 10:21:23 -0400 Received: from mail-bw0-f222.google.com ([209.85.218.222]:64282 "EHLO mail-bw0-f222.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751124AbZHMOVX convert rfc822-to-8bit (ORCPT ); Thu, 13 Aug 2009 10:21:23 -0400 DomainKey-Signature: a=rsa-sha1; c=nofws; d=gmail.com; s=gamma; h=mime-version:in-reply-to:references:date:message-id:subject:from:to :cc:content-type:content-transfer-encoding; b=pWJoAtult5t2N2macEKimcuWXOJsfPvJUc7PzbXw3Q29X5WZ/60oXUOXRCv224hU1i AlI6vGqoaNBL7u37uaNQNEX50SbQCaViYlO3tzzviZ56Bed++8EZFCEovxwr/SABn2mK GfgWCR+Uz2tzRbISPv5E5XsoOutGNbMnz3gMs= MIME-Version: 1.0 In-Reply-To: <1250166687-17673-2-git-send-email-borislav.petkov@amd.com> References: <20090813122337.GB7029@aftab> <1250166687-17673-2-git-send-email-borislav.petkov@amd.com> Date: Thu, 13 Aug 2009 10:21:22 -0400 Message-ID: <73c1f2160908130721y3c14c4e7h1ff967bac867d7e6@mail.gmail.com> Subject: Re: [PATCH 2/2] x86: Clear incorrectly forced X86_FEATURE_LAHF_LM flag From: Brian Gerst To: Borislav Petkov Cc: kjwinchester@gmail.com, mikpe@it.uu.se, mingo@elte.hu, linux-kernel@vger.kernel.org Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8BIT Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu, Aug 13, 2009 at 8:31 AM, Borislav Petkov wrote: > From: Kevin Winchester > > Due to an erratum with certain AMD Athlon 64 processors, the BIOS may > need to force enable the LAHF_LM capability.  Unfortunately, in at > least one case, the BIOS does this even for processors that do not > support the functionality. > > Add a specific check that will clear the feature bit for processors > known not to support the LAHF/SAHF instructions. > > Borislav: turn off cpuid bit. > > Signed-off-by: Kevin Winchester > Signed-off-by: Borislav Petkov > --- >  arch/x86/kernel/cpu/amd.c |   16 ++++++++++++++++ >  1 files changed, 16 insertions(+), 0 deletions(-) > > diff --git a/arch/x86/kernel/cpu/amd.c b/arch/x86/kernel/cpu/amd.c > index e2485b0..9cd6fc7 100644 > --- a/arch/x86/kernel/cpu/amd.c > +++ b/arch/x86/kernel/cpu/amd.c > @@ -400,6 +400,22 @@ static void __cpuinit init_amd(struct cpuinfo_x86 *c) >                level = cpuid_eax(1); >                if((level >= 0x0f48 && level < 0x0f50) || level >= 0x0f58) >                        set_cpu_cap(c, X86_FEATURE_REP_GOOD); > + > +               /* > +                * Some BIOSes incorrectly force this feature, but only K8 > +                * revision D (model = 0x14) and later actually support it. > +                */ > +               if (c->x86_model < 0x14) { Shouldn't you test that the flag is actually set before trying to clear it? > +                       u64 val; > + > +                       clear_cpu_cap(c, X86_FEATURE_LAHF_LM); > +                       if (!rdmsrl_amd_safe(0xc001100d, &val)) { > +                               val &= ~(1ULL << 32); > +                               wrmsr_amd_safe(0xc001100d, (u32) val, > +                                                          (u32)(val >> 32)); > +                       } > +               } > + >        } >        if (c->x86 == 0x10 || c->x86 == 0x11) >                set_cpu_cap(c, X86_FEATURE_REP_GOOD); > -- > 1.6.3.3 > > > -- > To unsubscribe from this list: send the line "unsubscribe linux-kernel" in > the body of a message to majordomo@vger.kernel.org > More majordomo info at  http://vger.kernel.org/majordomo-info.html > Please read the FAQ at  http://www.tux.org/lkml/ >