From 6b0f43ddfa358dc71ad2a2d57bce5906c1c5dc1a Mon Sep 17 00:00:00 2001 From: Borislav Petkov Date: Mon, 31 Aug 2009 09:50:11 +0200 Subject: [PATCH] x86, AMD: Disable wrongly set X86_FEATURE_LAHF_LM CPUID bit fbd8b1819e80ac5a176d085fdddc3a34d1499318 turns off the bit for /proc/cpuinfo. However, a proper/full fix would be to additionally turn off the bit in the CPUID output so that future callers get correct CPU features info. Do that by basically reversing what the BIOS wrongfully does at boot. Signed-off-by: Borislav Petkov LKML-Reference: <1251705011-18636-3-git-send-email-petkovbb@gmail.com> Signed-off-by: H. Peter Anvin --- arch/x86/kernel/cpu/amd.c | 11 ++++++++++- 1 file changed, 10 insertions(+), 1 deletion(-) diff --git a/arch/x86/kernel/cpu/amd.c b/arch/x86/kernel/cpu/amd.c index 63fddcd082c..0a717fc6aeb 100644 --- a/arch/x86/kernel/cpu/amd.c +++ b/arch/x86/kernel/cpu/amd.c @@ -404,9 +404,18 @@ static void __cpuinit init_amd(struct cpuinfo_x86 *c) /* * Some BIOSes incorrectly force this feature, but only K8 * revision D (model = 0x14) and later actually support it. + * (AMD Erratum #110, docId: 25759). */ - if (c->x86_model < 0x14) + if (c->x86_model < 0x14 && cpu_has(c, X86_FEATURE_LAHF_LM)) { + u64 val; + clear_cpu_cap(c, X86_FEATURE_LAHF_LM); + if (!rdmsrl_amd_safe(0xc001100d, &val)) { + val &= ~(1ULL << 32); + wrmsrl_amd_safe(0xc001100d, val); + } + } + } if (c->x86 == 0x10 || c->x86 == 0x11) set_cpu_cap(c, X86_FEATURE_REP_GOOD);