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Date:   Tue,  4 Apr 2017 15:14:06 -0400
From:   kan.liang@...el.com
To:     mingo@...hat.com, peterz@...radead.org,
        linux-kernel@...r.kernel.org
Cc:     eranian@...gle.com, ak@...ux.intel.com,
        Kan Liang <kan.liang@...el.com>
Subject: [PATCH V2] perf/x86: fix spurious NMI with PEBS Load Latency event

From: Kan Liang <kan.liang@...el.com>

Spurious NMIs will be observed when applying the following command.
   while true ; do sudo perf record -b -a -e
   "cpu/umask=0x01,event=0xcd,ldlat=0x80/pp,cpu/umask=0x03,event=0x0/,
    cpu/umask=0x02,event=0x0/,cycles,branches,cache-misses,
    cache-references" -- sleep 10 ; done

The issue was introduced by
commit 8077eca079a2 ("perf/x86/pebs: Add workaround for broken OVFL
status on HSW+")

The previous patch clear the status's bits for the counters used for
PEBS events, by masking the whole 64 bits pebs_enabled.
However, only the lower 32 bits of both status and pebs_enabled are
reserved for PEBS-able counters.
For status, the first three bits of upper 32 bits are fixed counter
overflow bit.
For pebs_enabled, the first three bits of upper 32 bits are for PEBS
Load Latency event.
In the test case, the PEBS Load Latency event and fixed counter event
could be overflowed 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.

Fixes: 8077eca079a2 ("perf/x86/pebs: Add workaround for broken OVFL
status on HSW+")
Signed-off-by: Kan Liang <kan.liang@...el.com>
---

Change since V1:
 - using a macros for (1ULL << MAX_PEBS_EVENTS) - 1)

 arch/x86/events/intel/core.c | 2 +-
 arch/x86/events/intel/ds.c   | 2 +-
 arch/x86/events/perf_event.h | 1 +
 3 files changed, 3 insertions(+), 2 deletions(-)

diff --git a/arch/x86/events/intel/core.c b/arch/x86/events/intel/core.c
index 319da60..3411e79 100644
--- a/arch/x86/events/intel/core.c
+++ b/arch/x86/events/intel/core.c
@@ -2151,7 +2151,7 @@ static int intel_pmu_handle_irq(struct pt_regs *regs)
 	 * counters from the GLOBAL_STATUS mask and we always process PEBS
 	 * events via drain_pebs().
 	 */
-	status &= ~cpuc->pebs_enabled;
+	status &= ~(cpuc->pebs_enabled & PEBS_COUNTER_MASK);
 
 	/*
 	 * PEBS overflow sets bit 62 in the global status register
diff --git a/arch/x86/events/intel/ds.c b/arch/x86/events/intel/ds.c
index 9dfeeec..c6d23ff 100644
--- a/arch/x86/events/intel/ds.c
+++ b/arch/x86/events/intel/ds.c
@@ -1222,7 +1222,7 @@ get_next_pebs_record_by_bit(void *base, void *top, int bit)
 
 			/* clear non-PEBS bit and re-check */
 			pebs_status = p->status & cpuc->pebs_enabled;
-			pebs_status &= (1ULL << MAX_PEBS_EVENTS) - 1;
+			pebs_status &= PEBS_COUNTER_MASK;
 			if (pebs_status == (1 << bit))
 				return at;
 		}
diff --git a/arch/x86/events/perf_event.h b/arch/x86/events/perf_event.h
index 416f565..2469fba 100644
--- a/arch/x86/events/perf_event.h
+++ b/arch/x86/events/perf_event.h
@@ -79,6 +79,7 @@ struct amd_nb {
 
 /* The maximal number of PEBS events: */
 #define MAX_PEBS_EVENTS		8
+#define PEBS_COUNTER_MASK	((1ULL << MAX_PEBS_EVENTS) - 1)
 
 /*
  * Flags PEBS can handle without an PMI.
-- 
2.4.3

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