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    Subject[tip:perf/urgent] perf/x86: Fix microcode revision check for SNB-PEBS
    Commit-ID:  e3e45c01ae690e65f2650e5288b9af802e95a136
    Gitweb: http://git.kernel.org/tip/e3e45c01ae690e65f2650e5288b9af802e95a136
    Author: Stephane Eranian <eranian@google.com>
    AuthorDate: Fri, 24 Aug 2012 15:34:34 +0200
    Committer: Ingo Molnar <mingo@kernel.org>
    CommitDate: Mon, 27 Aug 2012 08:48:19 +0200

    perf/x86: Fix microcode revision check for SNB-PEBS

    The following patch 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.

    Signed-off-by: Stephane Eranian <eranian@google.com>
    Acked-by: Borislav Petkov <borislav.petkov@amd.com>
    Cc: peterz@infradead.org
    Cc: andi@firstfloor.org
    Link: http://lkml.kernel.org/r/20120824133434.GA8014@quad
    Signed-off-by: Ingo Molnar <mingo@kernel.org>
    ---
    arch/x86/kernel/microcode_core.c | 3 +++
    1 files changed, 3 insertions(+), 0 deletions(-)

    diff --git a/arch/x86/kernel/microcode_core.c b/arch/x86/kernel/microcode_core.c
    index 4873e62..9e5bcf1 100644
    --- 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();


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