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    SubjectRe: [PATCH] perf/x86: fix microcode revision check for SNB-PEBS
    On Fri, Aug 24, 2012 at 03:34:34PM +0200, Stephane Eranian wrote:
    >
    > The following patch, relative to 3.6.0-rc3, makes
    > the microcode update code path actually invoke the
    > perf_check_microcode() function and thus potentially
    > renabling SNB PEBS.
    >
    > By default, CONFIG_MICROCODE_OLD_INTERFACE is
    > forced to Y in arch/x86/Kconfig. There is no
    > way to disable this. That means that the code
    > path used in arch/x86/kernel/microcode_core.c
    > did not include the call to perf_check_microcode().
    >
    > Thus, even though the microcode was updated to a
    > version that fixes the SNB PEBS problem, perf_event
    > would still return EOPNOTSUPP when enabling precise
    > sampling.
    >
    > This patch simply adds a call to perf_check_microcode()
    > in the call path used when OLD_INTERFACE=y.

    Ok, so c93dc84cbe324 added calls to perf_check_microcode but it looks
    like you're updating the microcode from /dev/cpu/microcode, correct?

    And if so, the old interface got missed.

    Oh well, as long as we have to support it, we might as well add that
    perf call there - it will go when the interface goes anyway so until
    then:

    Acked-by: Borislav Petkov <borislav.petkov@amd.com>

    >
    > Signed-off-by: Stephane Eranian <eranian@google.com>
    > ---
    >
    > --- a/arch/x86/kernel/microcode_core.c
    > +++ b/arch/x86/kernel/microcode_core.c
    > @@ -225,6 +225,9 @@ static ssize_t microcode_write(struct file *file, const char __user *buf,
    > if (do_microcode_update(buf, len) == 0)
    > ret = (ssize_t)len;
    >
    > + if (ret > 0)
    > + perf_check_microcode();
    > +
    > mutex_unlock(&microcode_mutex);
    > put_online_cpus();
    >
    >

    Thanks.

    --
    Regards/Gruss,
    Boris.

    Advanced Micro Devices GmbH
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