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Kan Liang e4557c1a46 perf/x86/intel: Fix spurious NMI on fixed counter 
If a user first sample a PEBS event on a fixed counter, then sample a
non-PEBS event on the same fixed counter on Icelake, it will trigger
spurious NMI. For example:

  perf record -e 'cycles:p' -a
  perf record -e 'cycles' -a

The error message for spurious NMI:

  [June 21 15:38] Uhhuh. NMI received for unknown reason 30 on CPU 2.
  [    +0.000000] Do you have a strange power saving mode enabled?
  [    +0.000000] Dazed and confused, but trying to continue

The bug was introduced by the following commit:

  commit 6f55967ad9 ("perf/x86/intel: Fix race in intel_pmu_disable_event()")

The commit moves the intel_pmu_pebs_disable() after intel_pmu_disable_fixed(),
which returns immediately.  The related bit of PEBS_ENABLE MSR will never be
cleared for the fixed counter. Then a non-PEBS event runs on the fixed counter,
but the bit on PEBS_ENABLE is still set, which triggers spurious NMIs.

Check and disable PEBS for fixed counters after intel_pmu_disable_fixed().

Reported-by: Yi, Ammy <ammy.yi@intel.com>
Signed-off-by: Kan Liang <kan.liang@linux.intel.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Acked-by: Jiri Olsa <jolsa@kernel.org>
Cc: <stable@vger.kernel.org>
Cc: Alexander Shishkin <alexander.shishkin@linux.intel.com>
Cc: Arnaldo Carvalho de Melo <acme@redhat.com>
Cc: Jiri Olsa <jolsa@redhat.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Stephane Eranian <eranian@google.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Vince Weaver <vincent.weaver@maine.edu>
Fixes: 6f55967ad9 ("perf/x86/intel: Fix race in intel_pmu_disable_event()")
Link: https://lkml.kernel.org/r/20190625142135.22112-1-kan.liang@linux.intel.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>
2019-07-13 11:21:29 +02:00
arch perf/x86/intel: Fix spurious NMI on fixed counter 2019-07-13 11:21:29 +02:00
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README 

Linux kernel
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There are several guides for kernel developers and users. These guides can
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In order to build the documentation, use ``make htmldocs`` or
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There are various text files in the Documentation/ subdirectory,
several of them using the Restructured Text markup notation.

Please read the Documentation/process/changes.rst file, as it contains the
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