linux-kernel - [PATCH 5.13 346/800] perf: Fix task context PMU for Hetero

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Message-Id: <20210712061003.817282982@linuxfoundation.org>
Date:   Mon, 12 Jul 2021 08:06:09 +0200
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     linux-kernel@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        stable@...r.kernel.org, Kan Liang <kan.liang@...ux.intel.com>,
        "Peter Zijlstra (Intel)" <peterz@...radead.org>,
        Sasha Levin <sashal@...nel.org>
Subject: [PATCH 5.13 346/800] perf: Fix task context PMU for Hetero

From: Peter Zijlstra <peterz@...radead.org>

[ Upstream commit 012669c740e6e2afa8bdb95394d06676f933dd2d ]

On HETEROGENEOUS hardware (ARM big.Little, Intel Alderlake etc.) each
CPU might have a different hardware PMU. Since each such PMU is
represented by a different struct pmu, but we only have a single HW
task context.

That means that the task context needs to switch PMU type when it
switches CPUs.

Not doing this means that ctx->pmu calls (pmu_{dis,en}able(),
{start,commit,cancel}_txn() etc.) are called against the wrong PMU and
things will go wobbly.

Fixes: f83d2f91d259 ("perf/x86/intel: Add Alder Lake Hybrid support")
Reported-by: Kan Liang <kan.liang@...ux.intel.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@...radead.org>
Tested-by: Kan Liang <kan.liang@...ux.intel.com>
Link: https://lkml.kernel.org/r/YMsy7BuGT8nBTspT@hirez.programming.kicks-ass.net
Signed-off-by: Sasha Levin <sashal@...nel.org>
---
 kernel/events/core.c | 9 ++++++++-
 1 file changed, 8 insertions(+), 1 deletion(-)

diff --git a/kernel/events/core.c b/kernel/events/core.c
index fe88d6eea3c2..9ebac2a79467 100644
--- a/kernel/events/core.c
+++ b/kernel/events/core.c
@@ -3821,9 +3821,16 @@ static void perf_event_context_sched_in(struct perf_event_context *ctx,
 					struct task_struct *task)
 {
 	struct perf_cpu_context *cpuctx;
-	struct pmu *pmu = ctx->pmu;
+	struct pmu *pmu;
 
 	cpuctx = __get_cpu_context(ctx);
+
+	/*
+	 * HACK: for HETEROGENEOUS the task context might have switched to a
+	 * different PMU, force (re)set the context,
+	 */
+	pmu = ctx->pmu = cpuctx->ctx.pmu;
+
 	if (cpuctx->task_ctx == ctx) {
 		if (cpuctx->sched_cb_usage)
 			__perf_pmu_sched_task(cpuctx, true);
-- 
2.30.2