Re: [tip:x86/urgent] x86, AMD: Disable wrongly set X86_FEATURE_LAHF_LM CPUID bit

Ingo Molnar
2009-08-16T20:51:26Z

* Kevin Winchester <kjwinchester@gmail.com> wrote:

> Ingo Molnar wrote:
> > * tip-bot for Borislav Petkov <borislav.petkov@amd.com> wrote:
> >
> >> Commit-ID: c74cb13b94118ec89e48849806356b67caa5ff86
> >> Gitweb: http://git.kernel.org/tip/c74cb13b94118ec89e48849806356b67caa5ff86
> >> Author: Borislav Petkov <borislav.petkov@amd.com>
> >> AuthorDate: Fri, 14 Aug 2009 14:06:34 +0200
> >> Committer: Ingo Molnar <mingo@elte.hu>
> >> CommitDate: Sat, 15 Aug 2009 18:43:59 +0200
> >>
> >> 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.
> >>
> >> Tested-by: Kevin Winchester <kjwinchester@gmail.com>
> >> Signed-off-by: Borislav Petkov <borislav.petkov@amd.com>
> >> Cc: kjwinchester@gmail.com
> >> Cc: mikpe@it.uu.se
> >> Cc: brgerst@gmail.com
> >> LKML-Reference: <1250251594-8348-2-git-send-email-borislav.petkov@amd.com>
> >> Signed-off-by: Ingo Molnar <mingo@elte.hu>
> >>
> >>
> >> ---
> >> arch/x86/kernel/cpu/amd.c | 12 +++++++++++-
> >> 1 files changed, 11 insertions(+), 1 deletions(-)
> >>
> >> diff --git a/arch/x86/kernel/cpu/amd.c b/arch/x86/kernel/cpu/amd.c
> >> index 63fddcd..0ee63dd 100644
> >> --- a/arch/x86/kernel/cpu/amd.c
> >> +++ b/arch/x86/kernel/cpu/amd.c
> >> @@ -404,9 +404,19 @@ 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);
> >> + wrmsr_amd_safe(0xc001100d, (u32) val,
> >> + (u32)(val >> 32));
> >> + }
> >> + }
> >> +
> >> }
> >> if (c->x86 == 0x10 || c->x86 == 0x11)
> >> set_cpu_cap(c, X86_FEATURE_REP_GOOD);
> >
> > -tip testing found this build bug caused by this patch:
> >
> > arch/x86/kernel/cpu/amd.c: In function ‘init_amd’:
> > arch/x86/kernel/cpu/amd.c:417: error: implicit declaration of function ‘wrmsr_amd_safe’
> >
>
> I didn't see a notification that patch 1/2:
>
> x86, msr: Add a AMD wrmsr with exception handling
>
> got applied before this patch. That could be the cause of this failure.

it got applied in the correct order:

c74cb13: x86, AMD: Disable wrongly set X86_FEATURE_LAHF_LM CPUID bit
0ae84a7: x86, msr: Add a AMD wrmsr with exception handling
3ef12c3: x86: Fix UV BAU destination subnode id
64f1607: Linux 2.6.31-rc6

Ingo