[PATCH 5.16 0450/1017] powerpc/perf: Dont use perf_hw_context for trace IMC PMU

[Greg Kroah-Hartman]

From: Athira Rajeev <atrajeev@xxxxxxxxxxxxxxxxxx>

[ Upstream commit 0198322379c25215b2778482bf1221743a76e2b5 ]

Trace IMC (In-Memory collection counters) in powerpc is useful for
application level profiling.

For trace_imc, presently task context (task_ctx_nr) is set to
perf_hw_context. But perf_hw_context should only be used for CPU PMU.
See commit 26657848502b ("perf/core: Verify we have a single
perf_hw_context PMU").

So for trace_imc, even though it is per thread PMU, it is preferred to
use sw_context in order to be able to do application level monitoring.
Hence change the task_ctx_nr to use perf_sw_context.

Fixes: 012ae244845f ("powerpc/perf: Trace imc PMU functions")
Signed-off-by: Athira Rajeev <atrajeev@xxxxxxxxxxxxxxxxxx>
Reviewed-by: Madhavan Srinivasan <maddy@xxxxxxxxxxxxxxxxxx>
[mpe: Update subject & incorporate notes into change log, reflow comment]
Signed-off-by: Michael Ellerman <mpe@xxxxxxxxxxxxxx>
Link: https://lore.kernel.org/r/20220202041837.65968-1-atrajeev@xxxxxxxxxxxxxxxxxx
Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>
---
 arch/powerpc/perf/imc-pmu.c | 6 +++++-
 1 file changed, 5 insertions(+), 1 deletion(-)

diff --git a/arch/powerpc/perf/imc-pmu.c b/arch/powerpc/perf/imc-pmu.c
index e106909ff9c3..e7583fbcc8fa 100644
--- a/arch/powerpc/perf/imc-pmu.c
+++ b/arch/powerpc/perf/imc-pmu.c
@@ -1457,7 +1457,11 @@ static int trace_imc_event_init(struct perf_event *event)
 
 	event->hw.idx = -1;
 
-	event->pmu->task_ctx_nr = perf_hw_context;
+	/*
+	 * There can only be a single PMU for perf_hw_context events which is assigned to
+	 * core PMU. Hence use "perf_sw_context" for trace_imc.
+	 */
+	event->pmu->task_ctx_nr = perf_sw_context;
 	event->destroy = reset_global_refc;
 	return 0;
 }
-- 
2.34.1