Messages in this thread Patch in this message | | | Date | Sat, 08 Aug 2009 08:53:30 -0300 | From | Kevin Winchester <> | 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 <kjwinchester@gmail.com> ---
While making this change, I noticed the clause above my code:
if((level >= 0x0f48 && level < 0x0f50) || level >= 0x0f58)
It does not seem concerned with the possibility that some of the upper 16 bits of level will be non-zero. Is this intentional, or should the upper 16 bits be masked off before the comparisons?
arch/x86/kernel/cpu/amd.c | 8 ++++++++ 1 files changed, 8 insertions(+), 0 deletions(-)
diff --git a/arch/x86/kernel/cpu/amd.c b/arch/x86/kernel/cpu/amd.c index e2485b0..a2f0fe4 100644 --- a/arch/x86/kernel/cpu/amd.c +++ b/arch/x86/kernel/cpu/amd.c @@ -400,6 +400,14 @@ 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 set this feature, but only + * Revision E (with Extended Model = 2) actually supports + * it. + */ + if (!(level & 0x00020000)) + clear_cpu_cap(c, X86_FEATURE_LAHF_LM); } if (c->x86 == 0x10 || c->x86 == 0x11) set_cpu_cap(c, X86_FEATURE_REP_GOOD); -- 1.6.4
| |