linux-kernel - [tip:perf/core] perf/x86/intel: Properly save/restore the PMU state in the NMI handler

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Message-ID: <tip-82d71ed0277efc45360828af8c4e4d40e1b45352@git.kernel.org>
Date:   Fri, 9 Mar 2018 01:08:18 -0800
From:   tip-bot for Kan Liang <tipbot@...or.com>
To:     linux-tip-commits@...r.kernel.org
Cc:     kan.liang@...ux.intel.com, peterz@...radead.org,
        torvalds@...ux-foundation.org, tglx@...utronix.de, acme@...hat.com,
        jolsa@...hat.com, alexander.shishkin@...ux.intel.com,
        hpa@...or.com, mingo@...nel.org, linux-kernel@...r.kernel.org,
        vincent.weaver@...ne.edu, fengguang.wu@...el.com,
        eranian@...gle.com
Subject: [tip:perf/core] perf/x86/intel: Properly save/restore the PMU state
 in the NMI handler

Commit-ID:  82d71ed0277efc45360828af8c4e4d40e1b45352
Gitweb:     https://git.kernel.org/tip/82d71ed0277efc45360828af8c4e4d40e1b45352
Author:     Kan Liang <kan.liang@...ux.intel.com>
AuthorDate: Tue, 20 Feb 2018 02:11:50 -0800
Committer:  Ingo Molnar <mingo@...nel.org>
CommitDate: Fri, 9 Mar 2018 08:22:18 +0100

perf/x86/intel: Properly save/restore the PMU state in the NMI handler

The PMU is disabled in intel_pmu_handle_irq(), but cpuc->enabled is not updated
accordingly.

This is fine in current usage because no-one checks it - but fix it
for future code: for example, the drain_pebs() will be modified to
fix an auto-reload bug.

Properly save/restore the old PMU state.

Signed-off-by: Kan Liang <kan.liang@...ux.intel.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@...radead.org>
Cc: Alexander Shishkin <alexander.shishkin@...ux.intel.com>
Cc: Arnaldo Carvalho de Melo <acme@...hat.com>
Cc: Jiri Olsa <jolsa@...hat.com>
Cc: Linus Torvalds <torvalds@...ux-foundation.org>
Cc: Peter Zijlstra <peterz@...radead.org>
Cc: Stephane Eranian <eranian@...gle.com>
Cc: Thomas Gleixner <tglx@...utronix.de>
Cc: Vince Weaver <vincent.weaver@...ne.edu>
Cc: acme@...nel.org
Cc: kernel test robot <fengguang.wu@...el.com>
Link: http://lkml.kernel.org/r/6f44ee84-56f8-79f1-559b-08e371eaeb78@linux.intel.com
Signed-off-by: Ingo Molnar <mingo@...nel.org>
---
 arch/x86/events/intel/core.c | 10 +++++++++-
 1 file changed, 9 insertions(+), 1 deletion(-)

diff --git a/arch/x86/events/intel/core.c b/arch/x86/events/intel/core.c
index 6b6c1717787d..1ba7ca7b675d 100644
--- a/arch/x86/events/intel/core.c
+++ b/arch/x86/events/intel/core.c
@@ -2201,9 +2201,15 @@ static int intel_pmu_handle_irq(struct pt_regs *regs)
 	int bit, loops;
 	u64 status;
 	int handled;
+	int pmu_enabled;
 
 	cpuc = this_cpu_ptr(&cpu_hw_events);
 
+	/*
+	 * Save the PMU state.
+	 * It needs to be restored when leaving the handler.
+	 */
+	pmu_enabled = cpuc->enabled;
 	/*
 	 * No known reason to not always do late ACK,
 	 * but just in case do it opt-in.
@@ -2211,6 +2217,7 @@ static int intel_pmu_handle_irq(struct pt_regs *regs)
 	if (!x86_pmu.late_ack)
 		apic_write(APIC_LVTPC, APIC_DM_NMI);
 	intel_bts_disable_local();
+	cpuc->enabled = 0;
 	__intel_pmu_disable_all();
 	handled = intel_pmu_drain_bts_buffer();
 	handled += intel_bts_interrupt();
@@ -2320,7 +2327,8 @@ again:
 
 done:
 	/* Only restore PMU state when it's active. See x86_pmu_disable(). */
-	if (cpuc->enabled)
+	cpuc->enabled = pmu_enabled;
+	if (pmu_enabled)
 		__intel_pmu_enable_all(0, true);
 	intel_bts_enable_local();