perf/x86: fix PEBS issues on Intel Atom/Core2

This change “perf/x86: fix PEBS issues on Intel Atom/Core2″ in Linux kernel is authored by Stephane Eranian <eranian [at] google.com> on Thu Dec 3 23:33:18 2015 +0100.

perf/x86: fix PEBS issues on Intel Atom/Core2

This patch fixes broken PEBS support on Intel Atom and Core2
due to wrong pointer arithmetic in intel_pmu_drain_pebs_core().

The get_next_pebs_record_by_bit() was called on PEBS format fmt0
which does not use the pebs_record_nhm layout.

Signed-off-by: Stephane Eranian <eranian@google.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
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: Thomas Gleixner <tglx@linutronix.de>
Cc: Vince Weaver <vincent.weaver@maine.edu>
Cc: kan.liang@intel.com
Fixes: 21509084f999 ("perf/x86/intel: Handle multiple records in the PEBS buffer")
Link: http://lkml.kernel.org/r/1449182000-31524-3-git-send-email-eranian@google.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>

This Linux change may have been applied to various maintained Linux releases and you can find Linux releases including commit 1424a09.

There are 9 lines of Linux source code added/deleted in this change. Code changes to Linux kernel are as follows.

 arch/x86/kernel/cpu/perf_event_intel_ds.c | 9 ++++++++-
 1 file changed, 8 insertions(+), 1 deletion(-)

diff --git a/arch/x86/kernel/cpu/perf_event_intel_ds.c b/arch/x86/kernel/cpu/perf_event_intel_ds.c
index 9c0f8d4..a7463ed 100644
--- a/arch/x86/kernel/cpu/perf_event_intel_ds.c
+++ b/arch/x86/kernel/cpu/perf_event_intel_ds.c
@@ -1106,6 +1106,13 @@ static void setup_pebs_sample_data(struct perf_event *event,
 	void *at;
 	u64 pebs_status;
 
+	/*
+	 * fmt0 does not have a status bitfield (does not use
+	 * perf_record_nhm format)
+	 */
+	if (x86_pmu.intel_cap.pebs_format < 1)
+		return base;
+
 	if (base == NULL)
 		return NULL;
 
@@ -1191,7 +1198,7 @@ static void intel_pmu_drain_pebs_core(struct pt_regs *iregs)
 	if (!event->attr.precise_ip)
 		return;
 
-	n = (top - at) / x86_pmu.pebs_record_size;
+	n = top - at;
 	if (n <= 0)
 		return;
 

The commit for this change in Linux stable tree is 1424a09 (patch).

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