Commit 16812c96 authored by Kan Liang's avatar Kan Liang Committed by Joerg Roedel
Browse files

iommu/vt-d: Fix an IOMMU perfmon warning when CPU hotplug 



A warning can be triggered when hotplug CPU 0.
$ echo 0 > /sys/devices/system/cpu/cpu0/online

 ------------[ cut here ]------------
 Voluntary context switch within RCU read-side critical section!
 WARNING: CPU: 0 PID: 19 at kernel/rcu/tree_plugin.h:318
          rcu_note_context_switch+0x4f4/0x580
 RIP: 0010:rcu_note_context_switch+0x4f4/0x580
 Call Trace:
  <TASK>
  ? perf_event_update_userpage+0x104/0x150
  __schedule+0x8d/0x960
  ? perf_event_set_state.part.82+0x11/0x50
  schedule+0x44/0xb0
  schedule_timeout+0x226/0x310
  ? __perf_event_disable+0x64/0x1a0
  ? _raw_spin_unlock+0x14/0x30
  wait_for_completion+0x94/0x130
  __wait_rcu_gp+0x108/0x130
  synchronize_rcu+0x67/0x70
  ? invoke_rcu_core+0xb0/0xb0
  ? __bpf_trace_rcu_stall_warning+0x10/0x10
  perf_pmu_migrate_context+0x121/0x370
  iommu_pmu_cpu_offline+0x6a/0xa0
  ? iommu_pmu_del+0x1e0/0x1e0
  cpuhp_invoke_callback+0x129/0x510
  cpuhp_thread_fun+0x94/0x150
  smpboot_thread_fn+0x183/0x220
  ? sort_range+0x20/0x20
  kthread+0xe6/0x110
  ? kthread_complete_and_exit+0x20/0x20
  ret_from_fork+0x1f/0x30
  </TASK>
 ---[ end trace 0000000000000000 ]---

The synchronize_rcu() will be invoked in the perf_pmu_migrate_context(),
when migrating a PMU to a new CPU. However, the current for_each_iommu()
is within RCU read-side critical section.

Two methods were considered to fix the issue.
- Use the dmar_global_lock to replace the RCU read lock when going
  through the drhd list. But it triggers a lockdep warning.
- Use the cpuhp_setup_state_multi() to set up a dedicated state for each
  IOMMU PMU. The lock can be avoided.

The latter method is implemented in this patch. Since each IOMMU PMU has
a dedicated state, add cpuhp_node and cpu in struct iommu_pmu to track
the state. The state can be dynamically allocated now. Remove the
CPUHP_AP_PERF_X86_IOMMU_PERF_ONLINE.

Fixes: 46284c6c ("iommu/vt-d: Support cpumask for IOMMU perfmon")
Reported-by: default avatarAmmy Yi <ammy.yi@intel.com>
Signed-off-by: default avatarKan Liang <kan.liang@linux.intel.com>
Link: https://lore.kernel.org/r/20230328182028.1366416-1-kan.liang@linux.intel.com


Signed-off-by: default avatarLu Baolu <baolu.lu@linux.intel.com>
Link: https://lore.kernel.org/r/20230329134721.469447-4-baolu.lu@linux.intel.com


Signed-off-by: default avatarJoerg Roedel <jroedel@suse.de>
parent bfd3c6b9

drivers/iommu/intel/iommu.h

+2 −0
Original line number Diff line number Diff line
@@ -641,6 +641,8 @@ struct iommu_pmu { 
	DECLARE_BITMAP(used_mask, IOMMU_PMU_IDX_MAX);

	struct perf_event	*event_list[IOMMU_PMU_IDX_MAX];

	unsigned char		irq_name[16];

	struct hlist_node	cpuhp_node;

	int			cpu;

};



#define IOMMU_IRQ_ID_OFFSET_PRQ		(DMAR_UNITS_SUPPORTED)

drivers/iommu/intel/perfmon.c

+44 −24
Original line number Diff line number Diff line
@@ -773,19 +773,34 @@ static void iommu_pmu_unset_interrupt(struct intel_iommu *iommu) 
	iommu->perf_irq = 0;

}



static int iommu_pmu_cpu_online(unsigned int cpu)

static int iommu_pmu_cpu_online(unsigned int cpu, struct hlist_node *node)

{

	struct iommu_pmu *iommu_pmu = hlist_entry_safe(node, typeof(*iommu_pmu), cpuhp_node);



	if (cpumask_empty(&iommu_pmu_cpu_mask))

		cpumask_set_cpu(cpu, &iommu_pmu_cpu_mask);



	if (cpumask_test_cpu(cpu, &iommu_pmu_cpu_mask))

		iommu_pmu->cpu = cpu;



	return 0;

}



static int iommu_pmu_cpu_offline(unsigned int cpu)

static int iommu_pmu_cpu_offline(unsigned int cpu, struct hlist_node *node)

{

	struct dmar_drhd_unit *drhd;

	struct intel_iommu *iommu;

	int target;

	struct iommu_pmu *iommu_pmu = hlist_entry_safe(node, typeof(*iommu_pmu), cpuhp_node);

	int target = cpumask_first(&iommu_pmu_cpu_mask);



	/*

	 * The iommu_pmu_cpu_mask has been updated when offline the CPU

	 * for the first iommu_pmu. Migrate the other iommu_pmu to the

	 * new target.

	 */

	if (target < nr_cpu_ids && target != iommu_pmu->cpu) {

		perf_pmu_migrate_context(&iommu_pmu->pmu, cpu, target);

		iommu_pmu->cpu = target;

		return 0;

	}



	if (!cpumask_test_and_clear_cpu(cpu, &iommu_pmu_cpu_mask))

		return 0;
@@ -795,45 +810,50 @@ static int iommu_pmu_cpu_offline(unsigned int cpu) 
	if (target < nr_cpu_ids)

		cpumask_set_cpu(target, &iommu_pmu_cpu_mask);

	else

		target = -1;



	rcu_read_lock();

		return 0;



	for_each_iommu(iommu, drhd) {

		if (!iommu->pmu)

			continue;

		perf_pmu_migrate_context(&iommu->pmu->pmu, cpu, target);

	}

	rcu_read_unlock();

	perf_pmu_migrate_context(&iommu_pmu->pmu, cpu, target);

	iommu_pmu->cpu = target;



	return 0;

}



static int nr_iommu_pmu;

static enum cpuhp_state iommu_cpuhp_slot;



static int iommu_pmu_cpuhp_setup(struct iommu_pmu *iommu_pmu)

{

	int ret;



	if (nr_iommu_pmu++)

		return 0;



	ret = cpuhp_setup_state(CPUHP_AP_PERF_X86_IOMMU_PERF_ONLINE,

	if (!nr_iommu_pmu) {

		ret = cpuhp_setup_state_multi(CPUHP_AP_ONLINE_DYN,

					      "driver/iommu/intel/perfmon:online",

					      iommu_pmu_cpu_online,

					      iommu_pmu_cpu_offline);

	if (ret)

		nr_iommu_pmu = 0;

		if (ret < 0)

			return ret;

		iommu_cpuhp_slot = ret;

	}



	ret = cpuhp_state_add_instance(iommu_cpuhp_slot, &iommu_pmu->cpuhp_node);

	if (ret) {

		if (!nr_iommu_pmu)

			cpuhp_remove_multi_state(iommu_cpuhp_slot);

		return ret;

	}

	nr_iommu_pmu++;



	return 0;

}



static void iommu_pmu_cpuhp_free(struct iommu_pmu *iommu_pmu)

{

	cpuhp_state_remove_instance(iommu_cpuhp_slot, &iommu_pmu->cpuhp_node);



	if (--nr_iommu_pmu)

		return;



	cpuhp_remove_state(CPUHP_AP_PERF_X86_IOMMU_PERF_ONLINE);

	cpuhp_remove_multi_state(iommu_cpuhp_slot);

}



void iommu_pmu_register(struct intel_iommu *iommu)

include/linux/cpuhotplug.h

+0 −1
Original line number Diff line number Diff line
@@ -218,7 +218,6 @@ enum cpuhp_state { 
	CPUHP_AP_PERF_X86_CQM_ONLINE,

	CPUHP_AP_PERF_X86_CSTATE_ONLINE,

	CPUHP_AP_PERF_X86_IDXD_ONLINE,

	CPUHP_AP_PERF_X86_IOMMU_PERF_ONLINE,

	CPUHP_AP_PERF_S390_CF_ONLINE,

	CPUHP_AP_PERF_S390_SF_ONLINE,

	CPUHP_AP_PERF_ARM_CCI_ONLINE,