From 628eaa4e877af8230ef7326d378e15d511c506ba Mon Sep 17 00:00:00 2001
From: Ian Rogers <irogers@google.com>
Date: Tue, 27 Jun 2023 11:28:34 -0700
Subject: perf pmus: Add placeholder core PMU

If loading a core PMU fails, legacy hardware/cache events may segv due
to there being no PMU. Create a placeholder empty PMU for this
case. This was discussed in:
https://lore.kernel.org/lkml/20230614151625.2077-1-yangjihong1@huawei.com/

Reported-by: Yang Jihong <yangjihong1@huawei.com>
Tested-by: Yang Jihong <yangjihong1@huawei.com>
Signed-off-by: Ian Rogers <irogers@google.com>
Cc: Ravi Bangoria <ravi.bangoria@amd.com>
Cc: James Clark <james.clark@arm.com>
Cc: Mark Rutland <mark.rutland@arm.com>
Cc: Suzuki Poulouse <suzuki.poulose@arm.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Adrian Hunter <adrian.hunter@intel.com>
Cc: Arnaldo Carvalho de Melo <acme@kernel.org>
Cc: Jiri Olsa <jolsa@kernel.org>
Cc: Rob Herring <robh@kernel.org>
Cc: Alexander Shishkin <alexander.shishkin@linux.intel.com>
Cc: Kan Liang <kan.liang@linux.intel.com>
Cc: Ingo Molnar <mingo@redhat.com>
Link: https://lore.kernel.org/r/20230627182834.117565-1-irogers@google.com
Signed-off-by: Namhyung Kim <namhyung@kernel.org>
---
 tools/perf/util/pmus.c | 7 ++++++-
 1 file changed, 6 insertions(+), 1 deletion(-)

(limited to 'tools/perf/util/pmus.c')

diff --git a/tools/perf/util/pmus.c b/tools/perf/util/pmus.c
index 0866dee3fc62..3cd9de42139e 100644
--- a/tools/perf/util/pmus.c
+++ b/tools/perf/util/pmus.c
@@ -153,7 +153,12 @@ static void pmu_read_sysfs(bool core_only)
 
 	closedir(dir);
 	if (core_only) {
-		read_sysfs_core_pmus = true;
+		if (!list_empty(&core_pmus))
+			read_sysfs_core_pmus = true;
+		else {
+			if (perf_pmu__create_placeholder_core_pmu(&core_pmus))
+				read_sysfs_core_pmus = true;
+		}
 	} else {
 		read_sysfs_core_pmus = true;
 		read_sysfs_all_pmus = true;
-- 
cgit