Messages in this thread Patch in this message | | | From | Borislav Petkov <> | Subject | [PATCH 2/2] x86: Clear incorrectly forced X86_FEATURE_LAHF_LM flag | Date | Thu, 13 Aug 2009 14:31:27 +0200 |
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From: Kevin Winchester <kjwinchester@gmail.com>
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 <kjwinchester@gmail.com> Signed-off-by: Borislav Petkov <borislav.petkov@amd.com> --- 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
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