• Kan Liang's avatar
    perf/x86: Fix spurious NMI with PEBS Load Latency event · fd583ad1
    Kan Liang authored
    Spurious NMIs will be observed with the following command:
      while :; do
        perf record -bae "cpu/umask=0x01,event=0xcd,ldlat=0x80/pp"
                      -e "cpu/umask=0x03,event=0x0/"
                      -e "cpu/umask=0x02,event=0x0/"
                      -e cycles,branches,cache-misses
                      -e cache-references -- sleep 10
    The bug was introduced by commit:
      8077eca0 ("perf/x86/pebs: Add workaround for broken OVFL status on HSW+")
    That commit clears the status bits for the counters used for PEBS
    events, by masking the whole 64 bits pebs_enabled. However, only the
    low 32 bits of both status and pebs_enabled are reserved for PEBS-able
    For status bits 32-34 are fixed counter overflow bits. For
    pebs_enabled bits 32-34 are for PEBS Load Latency.
    In the test case, the PEBS Load Latency event and fixed counter event
    could overflow at the same time. The fixed counter overflow bit will
    be cleared by mistake. Once it is cleared, the fixed counter overflow
    never be processed, which finally trigger spurious NMI.
    Correct the PEBS enabled mask by ignoring the non-PEBS bits.
    Signed-off-by: default avatarKan Liang <kan.liang@intel.com>
    Signed-off-by: default avatarPeter Zijlstra (Intel) <peterz@infradead.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: 8077eca0 ("perf/x86/pebs: Add workaround for broken OVFL status on HSW+")
    Link: http://lkml.kernel.org/r/1491333246-3965-1-git-send-email-kan.liang@intel.comSigned-off-by: default avatarIngo Molnar <mingo@kernel.org>
core.c 116 KB