[PATCH v4 2/4] KVM: arm64: PMU: Protect the list of PMUs with RCU

[Akihiko Odaki]

Convert the list of PMUs to a RCU-protected list that has primitives to
avoid read-side contention.

Signed-off-by: Akihiko Odaki <odaki@xxxxxxxxxxxxxxxxxxxxxx>
---
 arch/arm64/kvm/pmu-emul.c | 14 ++++++--------
 1 file changed, 6 insertions(+), 8 deletions(-)

diff --git a/arch/arm64/kvm/pmu-emul.c b/arch/arm64/kvm/pmu-emul.c
index 59ec96e09321..ef5140bbfe28 100644
--- a/arch/arm64/kvm/pmu-emul.c
+++ b/arch/arm64/kvm/pmu-emul.c
@@ -7,9 +7,9 @@
 #include <linux/cpu.h>
 #include <linux/kvm.h>
 #include <linux/kvm_host.h>
-#include <linux/list.h>
 #include <linux/perf_event.h>
 #include <linux/perf/arm_pmu.h>
+#include <linux/rculist.h>
 #include <linux/uaccess.h>
 #include <asm/kvm_emulate.h>
 #include <kvm/arm_pmu.h>
@@ -26,7 +26,6 @@ static bool kvm_pmu_counter_is_enabled(struct kvm_pmc *pmc);
 
 bool kvm_supports_guest_pmuv3(void)
 {
-	guard(mutex)(&arm_pmus_lock);
 	return !list_empty(&arm_pmus);
 }
 
@@ -808,7 +807,7 @@ void kvm_host_pmu_init(struct arm_pmu *pmu)
 		return;
 
 	entry->arm_pmu = pmu;
-	list_add_tail(&entry->entry, &arm_pmus);
+	list_add_tail_rcu(&entry->entry, &arm_pmus);
 }
 
 static struct arm_pmu *kvm_pmu_probe_armpmu(void)
@@ -817,7 +816,7 @@ static struct arm_pmu *kvm_pmu_probe_armpmu(void)
 	struct arm_pmu *pmu;
 	int cpu;
 
-	guard(mutex)(&arm_pmus_lock);
+	guard(rcu)();
 
 	/*
 	 * It is safe to use a stale cpu to iterate the list of PMUs so long as
@@ -837,7 +836,7 @@ static struct arm_pmu *kvm_pmu_probe_armpmu(void)
 	 * carried here.
 	 */
 	cpu = raw_smp_processor_id();
-	list_for_each_entry(entry, &arm_pmus, entry) {
+	list_for_each_entry_rcu(entry, &arm_pmus, entry) {
 		pmu = entry->arm_pmu;
 
 		if (cpumask_test_cpu(cpu, &pmu->supported_cpus))
@@ -1088,9 +1087,9 @@ static int kvm_arm_pmu_v3_set_pmu(struct kvm_vcpu *vcpu, int pmu_id)
 	int ret = -ENXIO;
 
 	lockdep_assert_held(&kvm->arch.config_lock);
-	mutex_lock(&arm_pmus_lock);
+	guard(rcu)();
 
-	list_for_each_entry(entry, &arm_pmus, entry) {
+	list_for_each_entry_rcu(entry, &arm_pmus, entry) {
 		arm_pmu = entry->arm_pmu;
 		if (arm_pmu->pmu.type == pmu_id) {
 			if (kvm_vm_has_ran_once(kvm) ||
@@ -1106,7 +1105,6 @@ static int kvm_arm_pmu_v3_set_pmu(struct kvm_vcpu *vcpu, int pmu_id)
 		}
 	}
 
-	mutex_unlock(&arm_pmus_lock);
 	return ret;
 }
 

-- 
2.53.0