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

Ingo Molnar
2009-08-16T06:41:45Z

* 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’

Ingo