From fbd8b1819e80ac5a176d085fdddc3a34d1499318 Mon Sep 17 00:00:00 2001 From: Kevin Winchester Date: Mon, 10 Aug 2009 19:56:45 -0300 Subject: [PATCH] x86: Clear incorrectly forced X86_FEATURE_LAHF_LM flag 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. Signed-off-by: Kevin Winchester Acked-by: Borislav Petkov LKML-Reference: <4A80A5AD.2000209@gmail.com> Signed-off-by: Ingo Molnar --- arch/x86/kernel/cpu/amd.c | 7 +++++++ 1 file changed, 7 insertions(+) diff --git a/arch/x86/kernel/cpu/amd.c b/arch/x86/kernel/cpu/amd.c index e2485b03f1cf..63fddcd082cd 100644 --- a/arch/x86/kernel/cpu/amd.c +++ b/arch/x86/kernel/cpu/amd.c @@ -400,6 +400,13 @@ 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) + clear_cpu_cap(c, X86_FEATURE_LAHF_LM); } if (c->x86 == 0x10 || c->x86 == 0x11) set_cpu_cap(c, X86_FEATURE_REP_GOOD); -- 2.20.1