From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754449AbZHMMbn (ORCPT ); Thu, 13 Aug 2009 08:31:43 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1754412AbZHMMbm (ORCPT ); Thu, 13 Aug 2009 08:31:42 -0400 Received: from va3ehsobe004.messaging.microsoft.com ([216.32.180.14]:22056 "EHLO VA3EHSOBE004.bigfish.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1751498AbZHMMbm (ORCPT ); Thu, 13 Aug 2009 08:31:42 -0400 X-SpamScore: 11 X-BigFish: VPS11(zza4b1ozz1202hzz5a6ciz32i203h43j62h) X-Spam-TCS-SCL: 1:0 X-FB-SS: 5, X-WSS-ID: 0KOBESJ-03-GL6-01 From: Borislav Petkov To: kjwinchester@gmail.com CC: mikpe@it.uu.se, , Subject: [PATCH 2/2] x86: Clear incorrectly forced X86_FEATURE_LAHF_LM flag Date: Thu, 13 Aug 2009 14:31:27 +0200 Message-ID: <1250166687-17673-2-git-send-email-borislav.petkov@amd.com> X-Mailer: git-send-email 1.6.3.3 In-Reply-To: <20090813122337.GB7029@aftab> References: <20090813122337.GB7029@aftab> X-OriginalArrivalTime: 13 Aug 2009 12:31:29.0082 (UTC) FILETIME=[FB5F29A0:01CA1C11] MIME-Version: 1.0 Content-Type: text/plain Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 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) { + 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