Patch "powerpc/perf: Don't use perf_hw_context for trace IMC PMU" has been added to the 5.17-stable tree

[Sasha Levin <sashal@xxxxxxxxxx>]

This is a note to let you know that I've just added the patch titled

    powerpc/perf: Don't use perf_hw_context for trace IMC PMU

to the 5.17-stable tree which can be found at:
    http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
     powerpc-perf-don-t-use-perf_hw_context-for-trace-imc.patch
and it can be found in the queue-5.17 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.



commit 0af19ae65b10fcbc094027764386bc6dfb3f2d7d
Author: Athira Rajeev <atrajeev@xxxxxxxxxxxxxxxxxx>
Date:   Wed Feb 2 09:48:37 2022 +0530

    powerpc/perf: Don't use perf_hw_context for trace IMC PMU
    
    [ 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>

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;
 }