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    Subject[tip:x86/urgent] x86, suspend: Handle CPUs which fail to #GP on RDMSR
    Commit-ID:  3a783f6e39cc6c89da8846312f29ca47affaa470
    Gitweb: http://git.kernel.org/tip/3a783f6e39cc6c89da8846312f29ca47affaa470
    Author: H. Peter Anvin <hpa@linux.intel.com>
    AuthorDate: Fri, 12 Jul 2013 16:48:12 -0700
    Committer: H. Peter Anvin <hpa@linux.intel.com>
    CommitDate: Fri, 12 Jul 2013 16:48:12 -0700

    x86, suspend: Handle CPUs which fail to #GP on RDMSR

    There are CPUs which have errata causing RDMSR of a nonexistent MSR to
    not fault. We would then try to WRMSR to restore the value of that
    MSR, causing a crash. Specifically, some Pentium M variants would
    have this problem trying to save and restore the non-existent EFER,
    causing a crash on resume.

    Work around this by making sure we can write back the result at
    suspend time.

    Huge thanks to Christian Sünkenberg for finding the offending erratum
    that finally deciphered the mystery.

    Reported-and-tested-by: Johan Heinrich <onny@project-insanity.org>
    Debugged-by: Christian Sünkenberg <christian.suenkenberg@student.kit.edu>
    Acked-by: Rafael J. Wysocki <rjw@sisk.pl>
    Link: http://lkml.kernel.org/r/51DDC972.3010005@student.kit.edu
    Cc: <stable@vger.kernel.org> # v3.7+
    ---
    arch/x86/kernel/acpi/sleep.c | 18 ++++++++++++++++--
    1 file changed, 16 insertions(+), 2 deletions(-)

    diff --git a/arch/x86/kernel/acpi/sleep.c b/arch/x86/kernel/acpi/sleep.c
    index 2a34aaf..3312010 100644
    --- a/arch/x86/kernel/acpi/sleep.c
    +++ b/arch/x86/kernel/acpi/sleep.c
    @@ -48,9 +48,20 @@ int x86_acpi_suspend_lowlevel(void)
    #ifndef CONFIG_64BIT
    native_store_gdt((struct desc_ptr *)&header->pmode_gdt);

    + /*
    + * We have to check that we can write back the value, and not
    + * just read it. At least on 90 nm Pentium M (Family 6, Model
    + * 13), reading an invalid MSR is not guaranteed to trap, see
    + * Erratum X4 in "Intel Pentium M Processor on 90 nm Process
    + * with 2-MB L2 Cache and Intel® Processor A100 and A110 on 90
    + * nm process with 512-KB L2 Cache Specification Update".
    + */
    if (!rdmsr_safe(MSR_EFER,
    &header->pmode_efer_low,
    - &header->pmode_efer_high))
    + &header->pmode_efer_high) &&
    + !wrmsr_safe(MSR_EFER,
    + header->pmode_efer_low,
    + header->pmode_efer_high))
    header->pmode_behavior |= (1 << WAKEUP_BEHAVIOR_RESTORE_EFER);
    #endif /* !CONFIG_64BIT */

    @@ -61,7 +72,10 @@ int x86_acpi_suspend_lowlevel(void)
    }
    if (!rdmsr_safe(MSR_IA32_MISC_ENABLE,
    &header->pmode_misc_en_low,
    - &header->pmode_misc_en_high))
    + &header->pmode_misc_en_high) &&
    + !wrmsr_safe(MSR_IA32_MISC_ENABLE,
    + header->pmode_misc_en_low,
    + header->pmode_misc_en_high))
    header->pmode_behavior |=
    (1 << WAKEUP_BEHAVIOR_RESTORE_MISC_ENABLE);
    header->realmode_flags = acpi_realmode_flags;
    --
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