linux-kernel - [PATCH v3 3/3] perf/x86/amd/core: Avoid register reset when CPU is dead

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Date: Mon, 29 Jan 2024 16:36:26 +0530
From: Sandipan Das <sandipan.das@....com>
To: <linux-perf-users@...r.kernel.org>, <linux-kernel@...r.kernel.org>
CC: <x86@...nel.org>, <peterz@...radead.org>, <mingo@...hat.com>,
	<acme@...nel.org>, <mark.rutland@....com>,
	<alexander.shishkin@...ux.intel.com>, <jolsa@...nel.org>,
	<namhyung@...nel.org>, <adrian.hunter@...el.com>, <tglx@...utronix.de>,
	<bp@...en8.de>, <eranian@...gle.com>, <irogers@...gle.com>,
	<mario.limonciello@....com>, <ravi.bangoria@....com>,
	<ananth.narayan@....com>, <sandipan.das@....com>
Subject: [PATCH v3 3/3] perf/x86/amd/core: Avoid register reset when CPU is dead

When bringing a CPU online, some of the PMC and LBR related registers
are reset. The same is done when a CPU is taken offline although that
is unnecessary. This currently happens in the "cpu_dead" callback which
is also incorrect as the callback runs on a control CPU instead of the
one that is being taken offline. This also affects hibernation and
suspend to RAM on some platforms as reported in the link below.

Link: https://lore.kernel.org/all/20231026170330.4657-3-mario.limonciello@amd.com/
Reported-by: Mario Limonciello <mario.limonciello@....com>
Fixes: 21d59e3e2c40 ("perf/x86/amd/core: Detect PerfMonV2 support")
Signed-off-by: Sandipan Das <sandipan.das@....com>
---
 arch/x86/events/amd/core.c | 1 -
 1 file changed, 1 deletion(-)

diff --git a/arch/x86/events/amd/core.c b/arch/x86/events/amd/core.c
index ffdfaee08b08..63514c311f44 100644
--- a/arch/x86/events/amd/core.c
+++ b/arch/x86/events/amd/core.c
@@ -604,7 +604,6 @@ static void amd_pmu_cpu_dead(int cpu)
 
 	kfree(cpuhw->lbr_sel);
 	cpuhw->lbr_sel = NULL;
-	amd_pmu_cpu_reset(cpu);
 
 	if (!x86_pmu.amd_nb_constraints)
 		return;
-- 
2.34.1