[PATCH 1/1] Return EINVAL when precise_ip perf events are requested on Arm

[James Clark]

ARM PMU events can be delivered with arbitrary skid, and there's
nothing the kernel can do to prevent this. Given that, the PMU
cannot support precise_ip != 0.

Also update comment to state that attr.config field is used to
set the event type rather than event_id which doesn't exist.

Signed-off-by: James Clark <james.clark@xxxxxxx>
Cc: Will Deacon <will@xxxxxxxxxx>
Cc: Mark Rutland <mark.rutland@xxxxxxx>
Cc: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
Cc: Ingo Molnar <mingo@xxxxxxxxxx>
Cc: Arnaldo Carvalho de Melo <acme@xxxxxxxxxx>
Cc: Alexander Shishkin <alexander.shishkin@xxxxxxxxxxxxxxx>
Cc: Jiri Olsa <jolsa@xxxxxxxxxx>
Cc: Tan Xiaojun <tanxiaojun@xxxxxxxxxx>
Cc: Al Grant <al.grant@xxxxxxx>
Cc: Namhyung Kim <namhyung@xxxxxxxxxx>
Cc: linux-arm-kernel@xxxxxxxxxxxxxxxxxxx
Cc: linux-kernel@xxxxxxxxxxxxxxx
---
 drivers/perf/arm_pmu.c          | 3 +++
 include/uapi/linux/perf_event.h | 4 ++--
 2 files changed, 5 insertions(+), 2 deletions(-)

diff --git a/drivers/perf/arm_pmu.c b/drivers/perf/arm_pmu.c
index df352b334ea7..4ddbdb93b3b6 100644
--- a/drivers/perf/arm_pmu.c
+++ b/drivers/perf/arm_pmu.c
@@ -102,6 +102,9 @@ armpmu_map_event(struct perf_event *event,
 	u64 config = event->attr.config;
 	int type = event->attr.type;
 
+	if (event->attr.precise)
+		return -EINVAL;
+
 	if (type == event->pmu->type)
 		return armpmu_map_raw_event(raw_event_mask, config);
 
diff --git a/include/uapi/linux/perf_event.h b/include/uapi/linux/perf_event.h
index 377d794d3105..3501b2eb168a 100644
--- a/include/uapi/linux/perf_event.h
+++ b/include/uapi/linux/perf_event.h
@@ -38,8 +38,8 @@ enum perf_type_id {
 };
 
 /*
- * Generalized performance event event_id types, used by the
- * attr.event_id parameter of the sys_perf_event_open()
+ * Generalized hardware performance event types, used by the
+ * attr.config parameter of the sys_perf_event_open()
  * syscall:
  */
 enum perf_hw_id {
-- 
2.24.0