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

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Date:   Wed, 15 Jan 2020 10:58:55 +0000
From:   James Clark <james.clark@....com>
To:     linux-arm-kernel@...ts.infradead.org
Cc:     nd@....com, James Clark <james.clark@....com>,
        Will Deacon <will@...nel.org>,
        Mark Rutland <mark.rutland@....com>,
        Peter Zijlstra <peterz@...radead.org>,
        Ingo Molnar <mingo@...hat.com>,
        Arnaldo Carvalho de Melo <acme@...nel.org>,
        Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
        Jiri Olsa <jolsa@...hat.com>,
        Tan Xiaojun <tanxiaojun@...wei.com>,
        Al Grant <al.grant@....com>,
        Namhyung Kim <namhyung@...nel.org>,
        linux-kernel@...r.kernel.org
Subject: [PATCH 1/1] Return EINVAL when precise_ip perf events are requested on Arm

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@....com>
Cc: Will Deacon <will@...nel.org>
Cc: Mark Rutland <mark.rutland@....com>
Cc: Peter Zijlstra <peterz@...radead.org>
Cc: Ingo Molnar <mingo@...hat.com>
Cc: Arnaldo Carvalho de Melo <acme@...nel.org>
Cc: Alexander Shishkin <alexander.shishkin@...ux.intel.com>
Cc: Jiri Olsa <jolsa@...hat.com>
Cc: Tan Xiaojun <tanxiaojun@...wei.com>
Cc: Al Grant <al.grant@....com>
Cc: Namhyung Kim <namhyung@...nel.org>
Cc: linux-arm-kernel@...ts.infradead.org
Cc: linux-kernel@...r.kernel.org
---
 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