[PATCH] drivers/perf: arm_pmu: Request PMU SPIs with IRQF_PER_CPU

[Will Deacon]

Since the PMU register interface is banked per CPU, CPU PMU interrrupts
cannot be handled by a CPU other than the one with the PMU asserting the
interrupt. This means that migrating PMU SPIs, as we do during a CPU
hotplug operation doesn't make any sense and can lead to the IRQ being
disabled entirely if we route a spurious IRQ to the new affinity target.

This has been observed in practice on AMD Seattle, where CPUs on the
non-boot cluster appear to take a spurious PMU IRQ when coming online,
which is routed to CPU0 where it cannot be handled.

This patch passes IRQF_PERCPU for PMU SPIs and forcefullt sets their
affinity prior to requesting them, ensuring that they cannot
be migrated during hotplug events.

Cc: Mark Rutland <mark.rutland at arm.com>
Fixes: 3cf7ee98b848 ("drivers/perf: arm_pmu: move irq request/free into probe")
Signed-off-by: Will Deacon <will.deacon at arm.com>
---
 drivers/perf/arm_pmu.c | 30 +++++++++++++++++-------------
 1 file changed, 17 insertions(+), 13 deletions(-)

diff --git a/drivers/perf/arm_pmu.c b/drivers/perf/arm_pmu.c
index dc459eb1246b..fa18e4858141 100644
--- a/drivers/perf/arm_pmu.c
+++ b/drivers/perf/arm_pmu.c
@@ -569,22 +569,32 @@ int armpmu_request_irq(struct arm_pmu *armpmu, int cpu)
 		if (irq != other_irq) {
 			pr_warn("mismatched PPIs detected.\n");
 			err = -EINVAL;
+			goto err_out;
 		}
 	} else {
+		err = irq_force_affinity(irq, cpumask_of(cpu));
+
+		if (err && num_possible_cpus() > 1) {
+			pr_warn("unable to set irq affinity (irq=%d, cpu=%u)\n",
+				irq, cpu);
+			goto err_out;
+		}
+
 		err = request_irq(irq, handler,
-				  IRQF_NOBALANCING | IRQF_NO_THREAD, "arm-pmu",
+				  IRQF_PERCPU | IRQF_NOBALANCING | IRQF_NO_THREAD,
+				  "arm-pmu",
 				  per_cpu_ptr(&hw_events->percpu_pmu, cpu));
 	}
 
-	if (err) {
-		pr_err("unable to request IRQ%d for ARM PMU counters\n",
-			irq);
-		return err;
-	}
+	if (err)
+		goto err_out;
 
 	cpumask_set_cpu(cpu, &armpmu->active_irqs);
-
 	return 0;
+
+err_out:
+	pr_err("unable to request IRQ%d for ARM PMU counters\n", irq);
+	return err;
 }
 
 int armpmu_request_irqs(struct arm_pmu *armpmu)
@@ -628,12 +638,6 @@ static int arm_perf_starting_cpu(unsigned int cpu, struct hlist_node *node)
 			enable_percpu_irq(irq, IRQ_TYPE_NONE);
 			return 0;
 		}
-
-		if (irq_force_affinity(irq, cpumask_of(cpu)) &&
-		    num_possible_cpus() > 1) {
-			pr_warn("unable to set irq affinity (irq=%d, cpu=%u)\n",
-				irq, cpu);
-		}
 	}
 
 	return 0;
-- 
2.1.4