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

    --
    Kevin Winchester

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