drivers/perf: xgene: Add CPU hotplug support

If the CPU assigned to the xgene PMU is taken offline, then subsequent
perf invocations on the PMU will fail:

  # echo 0 > /sys/devices/system/cpu/cpu0/online
  # perf stat -a -e l3c0/cycle-count/,l3c0/write/ sleep 1
    Error:
    The sys_perf_event_open() syscall returned with 19 (No such device) for event (l3c0/cycle-count/).
    /bin/dmesg may provide additional information.
    No CONFIG_PERF_EVENTS=y kernel support configured?

This patch implements a hotplug notifier in the xgene PMU driver so that
the PMU context is migrated to another online CPU should its assigned
CPU disappear.
Acked-by: Mark Rutland <mark.rutland@arm.com>
Signed-off-by: Hoan Tran <hoan.tran@amperecomputing.com>
[will: Made naming of new cpuhp_state enum entry consistent]
Signed-off-by: Will Deacon <will.deacon@arm.com>

drivers/perf/xgene_pmu.c

@@ -21,6 +21,7 @@
 
 #include <linux/acpi.h>
 #include <linux/clk.h>
+#include <linux/cpuhotplug.h>
 #include <linux/cpumask.h>
 #include <linux/interrupt.h>
 #include <linux/io.h>
@@ -130,12 +131,14 @@ struct xgene_pmu_ops {
 
 struct xgene_pmu {
 	struct device *dev;
+	struct hlist_node node;
 	int version;
 	void __iomem *pcppmu_csr;
 	u32 mcb_active_mask;
 	u32 mc_active_mask;
 	u32 l3c_active_mask;
 	cpumask_t cpu;
+	int irq;
 	raw_spinlock_t lock;
 	const struct xgene_pmu_ops *ops;
 	struct list_head l3cpmus;
@@ -1806,6 +1809,53 @@ static const struct acpi_device_id xgene_pmu_acpi_match[] = {
 MODULE_DEVICE_TABLE(acpi, xgene_pmu_acpi_match);
 #endif
 
+static int xgene_pmu_online_cpu(unsigned int cpu, struct hlist_node *node)
+{
+	struct xgene_pmu *xgene_pmu = hlist_entry_safe(node, struct xgene_pmu,
+						       node);
+
+	if (cpumask_empty(&xgene_pmu->cpu))
+		cpumask_set_cpu(cpu, &xgene_pmu->cpu);
+
+	/* Overflow interrupt also should use the same CPU */
+	WARN_ON(irq_set_affinity(xgene_pmu->irq, &xgene_pmu->cpu));
+
+	return 0;
+}
+
+static int xgene_pmu_offline_cpu(unsigned int cpu, struct hlist_node *node)
+{
+	struct xgene_pmu *xgene_pmu = hlist_entry_safe(node, struct xgene_pmu,
+						       node);
+	struct xgene_pmu_dev_ctx *ctx;
+	unsigned int target;
+
+	if (!cpumask_test_and_clear_cpu(cpu, &xgene_pmu->cpu))
+		return 0;
+	target = cpumask_any_but(cpu_online_mask, cpu);
+	if (target >= nr_cpu_ids)
+		return 0;
+
+	list_for_each_entry(ctx, &xgene_pmu->mcpmus, next) {
+		perf_pmu_migrate_context(&ctx->pmu_dev->pmu, cpu, target);
+	}
+	list_for_each_entry(ctx, &xgene_pmu->mcbpmus, next) {
+		perf_pmu_migrate_context(&ctx->pmu_dev->pmu, cpu, target);
+	}
+	list_for_each_entry(ctx, &xgene_pmu->l3cpmus, next) {
+		perf_pmu_migrate_context(&ctx->pmu_dev->pmu, cpu, target);
+	}
+	list_for_each_entry(ctx, &xgene_pmu->iobpmus, next) {
+		perf_pmu_migrate_context(&ctx->pmu_dev->pmu, cpu, target);
+	}
+
+	cpumask_set_cpu(target, &xgene_pmu->cpu);
+	/* Overflow interrupt also should use the same CPU */
+	WARN_ON(irq_set_affinity(xgene_pmu->irq, &xgene_pmu->cpu));
+
+	return 0;
+}
+
 static int xgene_pmu_probe(struct platform_device *pdev)
 {
 	const struct xgene_pmu_data *dev_data;
@@ -1815,6 +1865,14 @@ static int xgene_pmu_probe(struct platform_device *pdev)
 	int irq, rc;
 	int version;
 
+	/* Install a hook to update the reader CPU in case it goes offline */
+	rc = cpuhp_setup_state_multi(CPUHP_AP_PERF_ARM_APM_XGENE_ONLINE,
+				      "CPUHP_AP_PERF_ARM_APM_XGENE_ONLINE",
+				      xgene_pmu_online_cpu,
+				      xgene_pmu_offline_cpu);
+	if (rc)
+		return rc;
+
 	xgene_pmu = devm_kzalloc(&pdev->dev, sizeof(*xgene_pmu), GFP_KERNEL);
 	if (!xgene_pmu)
 		return -ENOMEM;
@@ -1865,6 +1923,7 @@ static int xgene_pmu_probe(struct platform_device *pdev)
 		dev_err(&pdev->dev, "No IRQ resource\n");
 		return -EINVAL;
 	}
+
 	rc = devm_request_irq(&pdev->dev, irq, xgene_pmu_isr,
 				IRQF_NOBALANCING | IRQF_NO_THREAD,
 				dev_name(&pdev->dev), xgene_pmu);
@@ -1873,6 +1932,8 @@ static int xgene_pmu_probe(struct platform_device *pdev)
 		return rc;
 	}
 
+	xgene_pmu->irq = irq;
+
 	raw_spin_lock_init(&xgene_pmu->lock);
 
 	/* Check for active MCBs and MCUs */
@@ -1883,13 +1944,11 @@ static int xgene_pmu_probe(struct platform_device *pdev)
 		xgene_pmu->mc_active_mask = 0x1;
 	}
 
-	/* Pick one core to use for cpumask attributes */
-	cpumask_set_cpu(smp_processor_id(), &xgene_pmu->cpu);
-
-	/* Make sure that the overflow interrupt is handled by this CPU */
-	rc = irq_set_affinity(irq, &xgene_pmu->cpu);
+	/* Add this instance to the list used by the hotplug callback */
+	rc = cpuhp_state_add_instance(CPUHP_AP_PERF_ARM_APM_XGENE_ONLINE,
+				      &xgene_pmu->node);
 	if (rc) {
-		dev_err(&pdev->dev, "Failed to set interrupt affinity!\n");
+		dev_err(&pdev->dev, "Error %d registering hotplug", rc);
 		return rc;
 	}
 
@@ -1897,13 +1956,18 @@ static int xgene_pmu_probe(struct platform_device *pdev)
 	rc = xgene_pmu_probe_pmu_dev(xgene_pmu, pdev);
 	if (rc) {
 		dev_err(&pdev->dev, "No PMU perf devices found!\n");
-		return rc;
+		goto out_unregister;
 	}
 
 	/* Enable interrupt */
 	xgene_pmu->ops->unmask_int(xgene_pmu);
 
 	return 0;
+
+out_unregister:
+	cpuhp_state_remove_instance(CPUHP_AP_PERF_ARM_APM_XGENE_ONLINE,
+				    &xgene_pmu->node);
+	return rc;
 }
 
 static void
@@ -1924,6 +1988,8 @@ static int xgene_pmu_remove(struct platform_device *pdev)
 	xgene_pmu_dev_cleanup(xgene_pmu, &xgene_pmu->iobpmus);
 	xgene_pmu_dev_cleanup(xgene_pmu, &xgene_pmu->mcbpmus);
 	xgene_pmu_dev_cleanup(xgene_pmu, &xgene_pmu->mcpmus);
+	cpuhp_state_remove_instance(CPUHP_AP_PERF_ARM_APM_XGENE_ONLINE,
+				    &xgene_pmu->node);
 
 	return 0;
 }

include/linux/cpuhotplug.h

@@ -164,6 +164,7 @@ enum cpuhp_state {
 	CPUHP_AP_PERF_ARM_L2X0_ONLINE,
 	CPUHP_AP_PERF_ARM_QCOM_L2_ONLINE,
 	CPUHP_AP_PERF_ARM_QCOM_L3_ONLINE,
+	CPUHP_AP_PERF_ARM_APM_XGENE_ONLINE,
 	CPUHP_AP_PERF_POWERPC_NEST_IMC_ONLINE,
 	CPUHP_AP_PERF_POWERPC_CORE_IMC_ONLINE,
 	CPUHP_AP_PERF_POWERPC_THREAD_IMC_ONLINE,