perf list: Fix checking for supported events on older kernels

"perf list" listing of hardware events doesn't work on older ARM devices.
The change enabling event detection:

commit b41f1cec91c37eeea6fdb15effbfa24ea0a5536b
Author: Namhyung Kim <[e-mail]>
Date: Tue Aug 27 11:41:53 2013 +0900

perf list: Skip unsupported events

uses the following code in tools/perf/util/parse-events.c:

struct perf_event_attr attr = {
.type = type,
.config = config,
.disabled = 1,
.exclude_kernel = 1,
};

On ARM machines pre-dating the Cortex-A15 this doesn't work, as these
machines don't support .exclude_kernel. So starting with 3.12 "perf
list" does not report any hardware events at all on older machines (seen
on Rasp-Pi, Pandaboard, Beagleboard, etc).

This version of the patch makes changes suggested by Namhyung Kim to
check for EACCESS and retry (instead of just dropping the
exclude_kernel) so we can properly handle machines where
/proc/sys/kernel/perf_event_paranoid is set to 2.

Reported-by: Chad Paradis <[e-mail]>
Signed-off-by: Vince Weaver <[e-mail]>
Acked-by: Namhyung Kim <[e-mail]>
Cc: Chad Paradis <[e-mail]>
Cc: Ingo Molnar <[e-mail]>
Cc: Namhyung Kim <[e-mail]>
Cc: Paul Mackerras <[e-mail]>
Cc: Peter Zijlstra <[e-mail]>
Link: http://lkml.kernel.org/r/[e-mail]
Signed-off-by: Arnaldo Carvalho de Melo <[e-mail]>

tools/perf/util/parse-events.c

···
 static bool is_event_supported(u8 type, unsigned config)
 {
 	bool ret = true;
+	int open_return;
 	struct perf_evsel *evsel;
 	struct perf_event_attr attr = {
 		.type = type,
 		.config = config,
 		.disabled = 1,
-		.exclude_kernel = 1,
 	};
 	struct {
 		struct thread_map map;
···
 
 	evsel = perf_evsel__new(&attr);
 	if (evsel) {
-		ret = perf_evsel__open(evsel, NULL, &tmap.map) >= 0;
+		open_return = perf_evsel__open(evsel, NULL, &tmap.map);
+		ret = open_return >= 0;
+
+		if (open_return == -EACCES) {
+			/*
+			 * This happens if the paranoid value
+			 * /proc/sys/kernel/perf_event_paranoid is set to 2
+			 * Re-run with exclude_kernel set; we don't do that
+			 * by default as some ARM machines do not support it.
+			 *
+			 */
+			evsel->attr.exclude_kernel = 1;
+			ret = perf_evsel__open(evsel, NULL, &tmap.map) >= 0;
+		}
 		perf_evsel__delete(evsel);
 	}