linux-kernel - [PATCH v6 7/7] arm_pmu: arm64: Use NMIs for PMU

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Message-Id: <20200819133419.526889-8-alexandru.elisei@arm.com>
Date:   Wed, 19 Aug 2020 14:34:19 +0100
From:   Alexandru Elisei <alexandru.elisei@....com>
To:     linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org
Cc:     mark.rutland@....com, maz@...nel.org, will@...nel.org,
        catalin.marinas@....com, swboyd@...omium.org,
        sumit.garg@...aro.org, Julien Thierry <julien.thierry@....com>,
        Julien Thierry <julien.thierry.kdev@...il.com>,
        Will Deacon <will.deacon@....com>
Subject: [PATCH v6 7/7] arm_pmu: arm64: Use NMIs for PMU

From: Julien Thierry <julien.thierry@....com>

Add required PMU interrupt operations for NMIs. Request interrupt lines as
NMIs when possible, otherwise fall back to normal interrupts.

NMIs are only supported on the arm64 architecture with a GICv3 irqchip.

Cc: Julien Thierry <julien.thierry.kdev@...il.com>
Cc: Will Deacon <will.deacon@....com>
Cc: Mark Rutland <mark.rutland@....com>
Signed-off-by: Julien Thierry <julien.thierry@....com>
[Added that NMIs only work on arm64 + GICv3]
Signed-off-by: Alexandru Elisei <alexandru.elisei@....com>
---
 drivers/perf/arm_pmu.c | 62 ++++++++++++++++++++++++++++++++++++++----
 1 file changed, 56 insertions(+), 6 deletions(-)

diff --git a/drivers/perf/arm_pmu.c b/drivers/perf/arm_pmu.c
index 17e5952d21e4..dd9d7f61ee29 100644
--- a/drivers/perf/arm_pmu.c
+++ b/drivers/perf/arm_pmu.c
@@ -45,6 +45,17 @@ static const struct pmu_irq_ops pmuirq_ops = {
 	.free_pmuirq = armpmu_free_pmuirq
 };
 
+static void armpmu_free_pmunmi(unsigned int irq, int cpu, void __percpu *devid)
+{
+	free_nmi(irq, per_cpu_ptr(devid, cpu));
+}
+
+static const struct pmu_irq_ops pmunmi_ops = {
+	.enable_pmuirq = enable_nmi,
+	.disable_pmuirq = disable_nmi_nosync,
+	.free_pmuirq = armpmu_free_pmunmi
+};
+
 static void armpmu_enable_percpu_pmuirq(unsigned int irq)
 {
 	enable_percpu_irq(irq, IRQ_TYPE_NONE);
@@ -63,6 +74,31 @@ static const struct pmu_irq_ops percpu_pmuirq_ops = {
 	.free_pmuirq = armpmu_free_percpu_pmuirq
 };
 
+static void armpmu_enable_percpu_pmunmi(unsigned int irq)
+{
+	if (!prepare_percpu_nmi(irq))
+		enable_percpu_nmi(irq, IRQ_TYPE_NONE);
+}
+
+static void armpmu_disable_percpu_pmunmi(unsigned int irq)
+{
+	disable_percpu_nmi(irq);
+	teardown_percpu_nmi(irq);
+}
+
+static void armpmu_free_percpu_pmunmi(unsigned int irq, int cpu,
+				      void __percpu *devid)
+{
+	if (armpmu_count_irq_users(irq) == 1)
+		free_percpu_nmi(irq, devid);
+}
+
+static const struct pmu_irq_ops percpu_pmunmi_ops = {
+	.enable_pmuirq = armpmu_enable_percpu_pmunmi,
+	.disable_pmuirq = armpmu_disable_percpu_pmunmi,
+	.free_pmuirq = armpmu_free_percpu_pmunmi
+};
+
 static DEFINE_PER_CPU(struct arm_pmu *, cpu_armpmu);
 static DEFINE_PER_CPU(int, cpu_irq);
 static DEFINE_PER_CPU(const struct pmu_irq_ops *, cpu_irq_ops);
@@ -633,15 +669,29 @@ int armpmu_request_irq(int irq, int cpu)
 			    IRQF_NO_THREAD;
 
 		irq_set_status_flags(irq, IRQ_NOAUTOEN);
-		err = request_irq(irq, handler, irq_flags, "arm-pmu",
+
+		err = request_nmi(irq, handler, irq_flags, "arm-pmu",
 				  per_cpu_ptr(&cpu_armpmu, cpu));
 
-		irq_ops = &pmuirq_ops;
+		/* If cannot get an NMI, get a normal interrupt */
+		if (err) {
+			err = request_irq(irq, handler, irq_flags, "arm-pmu",
+					  per_cpu_ptr(&cpu_armpmu, cpu));
+			irq_ops = &pmuirq_ops;
+		} else {
+			irq_ops = &pmunmi_ops;
+		}
 	} else if (armpmu_count_irq_users(irq) == 0) {
-		err = request_percpu_irq(irq, handler, "arm-pmu",
-					 &cpu_armpmu);
-
-		irq_ops = &percpu_pmuirq_ops;
+		err = request_percpu_nmi(irq, handler, "arm-pmu", &cpu_armpmu);
+
+		/* If cannot get an NMI, get a normal interrupt */
+		if (err) {
+			err = request_percpu_irq(irq, handler, "arm-pmu",
+						 &cpu_armpmu);
+			irq_ops = &percpu_pmuirq_ops;
+		} else {
+			irq_ops = &percpu_pmunmi_ops;
+		}
 	} else {
 		/* Per cpudevid irq was already requested by another CPU */
 		irq_ops = armpmu_find_irq_ops(irq);
-- 
2.28.0