Messages in this thread | | | Date | Thu, 13 Aug 2009 10:21:22 -0400 | Subject | Re: [PATCH 2/2] x86: Clear incorrectly forced X86_FEATURE_LAHF_LM flag | From | Brian Gerst <> |
| |
On Thu, Aug 13, 2009 at 8:31 AM, Borislav Petkov<borislav.petkov@amd.com> wrote: > 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) {
Shouldn't you test that the flag is actually set before trying to clear it?
> + 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 > > > -- > To unsubscribe from this list: send the line "unsubscribe linux-kernel" in > the body of a message to majordomo@vger.kernel.org > More majordomo info at http://vger.kernel.org/majordomo-info.html > Please read the FAQ at http://www.tux.org/lkml/ > -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
| |