[tip:perf/core] perf intel-pt: Fix error with config term "pt=0"

[tip-bot for Adrian Hunter]

Commit-ID:  932d0166b1dbc2a631ac718615efc4917412ecf3
Gitweb:     https://git.kernel.org/tip/932d0166b1dbc2a631ac718615efc4917412ecf3
Author:     Adrian Hunter <adrian.hunter@xxxxxxxxx>
AuthorDate: Mon, 26 Nov 2018 14:12:52 +0200
Committer:  Arnaldo Carvalho de Melo <acme@xxxxxxxxxx>
CommitDate: Thu, 29 Nov 2018 20:42:49 -0300

perf intel-pt: Fix error with config term "pt=0"

Users should never use 'pt=0', but if they do it may give a meaningless
error:

	$ perf record -e intel_pt/pt=0/u uname
	Error:
	The sys_perf_event_open() syscall returned with 22 (Invalid argument) for
	event (intel_pt/pt=0/u).

Fix that by forcing 'pt=1'.

Committer testing:

  # perf record -e intel_pt/pt=0/u uname
  Error:
  The sys_perf_event_open() syscall returned with 22 (Invalid argument) for event (intel_pt/pt=0/u).
  /bin/dmesg | grep -i perf may provide additional information.

  # perf record -e intel_pt/pt=0/u uname
  pt=0 doesn't make sense, forcing pt=1
  Linux
  [ perf record: Woken up 1 times to write data ]
  [ perf record: Captured and wrote 0.020 MB perf.data ]
  #

Signed-off-by: Adrian Hunter <adrian.hunter@xxxxxxxxx>
Tested-by: Arnaldo Carvalho de Melo <acme@xxxxxxxxxx>
Cc: Jiri Olsa <jolsa@xxxxxxxxxx>
Link: http://lkml.kernel.org/r/b7c5b4e5-9497-10e5-fd43-5f3e4a0fe51d@xxxxxxxxx
Signed-off-by: Arnaldo Carvalho de Melo <acme@xxxxxxxxxx>
---
 tools/perf/arch/x86/util/intel-pt.c | 11 +++++++++++
 1 file changed, 11 insertions(+)

diff --git a/tools/perf/arch/x86/util/intel-pt.c b/tools/perf/arch/x86/util/intel-pt.c
index db0ba8caf5a2..ba8ecaf52200 100644
--- a/tools/perf/arch/x86/util/intel-pt.c
+++ b/tools/perf/arch/x86/util/intel-pt.c
@@ -524,10 +524,21 @@ static int intel_pt_validate_config(struct perf_pmu *intel_pt_pmu,
 				    struct perf_evsel *evsel)
 {
 	int err;
+	char c;
 
 	if (!evsel)
 		return 0;
 
+	/*
+	 * If supported, force pass-through config term (pt=1) even if user
+	 * sets pt=0, which avoids senseless kernel errors.
+	 */
+	if (perf_pmu__scan_file(intel_pt_pmu, "format/pt", "%c", &c) == 1 &&
+	    !(evsel->attr.config & 1)) {
+		pr_warning("pt=0 doesn't make sense, forcing pt=1\n");
+		evsel->attr.config |= 1;
+	}
+
 	err = intel_pt_val_config_term(intel_pt_pmu, "caps/cycle_thresholds",
 				       "cyc_thresh", "caps/psb_cyc",
 				       evsel->attr.config);