KVM: arm64: Keep a list of probed PMUs

The ARM PMU driver calls kvm_host_pmu_init() after probing to tell KVM that
a hardware PMU is available for guest emulation. Heterogeneous systems can
have more than one PMU present, and the callback gets called multiple
times, once for each of them. Keep track of all the PMUs available to KVM,
as they're going to be needed later.
Reviewed-by: NReiji Watanabe <reijiw@google.com>
Signed-off-by: NAlexandru Elisei <alexandru.elisei@arm.com>
Signed-off-by: NMarc Zyngier <maz@kernel.org>
Link: https://lore.kernel.org/r/20220127161759.53553-5-alexandru.elisei@arm.com

arch/arm64/kvm/pmu-emul.c

@@ -7,6 +7,7 @@
 #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/uaccess.h>
@@ -16,6 +17,9 @@
 
 DEFINE_STATIC_KEY_FALSE(kvm_arm_pmu_available);
 
+static LIST_HEAD(arm_pmus);
+static DEFINE_MUTEX(arm_pmus_lock);
+
 static void kvm_pmu_create_perf_event(struct kvm_vcpu *vcpu, u64 select_idx);
 static void kvm_pmu_update_pmc_chained(struct kvm_vcpu *vcpu, u64 select_idx);
 static void kvm_pmu_stop_counter(struct kvm_vcpu *vcpu, struct kvm_pmc *pmc);
@@ -750,9 +754,26 @@ void kvm_pmu_set_counter_event_type(struct kvm_vcpu *vcpu, u64 data,
 
 void kvm_host_pmu_init(struct arm_pmu *pmu)
 {
-	if (pmu->pmuver != 0 && pmu->pmuver != ID_AA64DFR0_PMUVER_IMP_DEF &&
-	    !kvm_arm_support_pmu_v3() && !is_protected_kvm_enabled())
+	struct arm_pmu_entry *entry;
+
+	if (pmu->pmuver == 0 || pmu->pmuver == ID_AA64DFR0_PMUVER_IMP_DEF ||
+	    is_protected_kvm_enabled())
+		return;
+
+	mutex_lock(&arm_pmus_lock);
+
+	entry = kmalloc(sizeof(*entry), GFP_KERNEL);
+	if (!entry)
+		goto out_unlock;
+
+	entry->arm_pmu = pmu;
+	list_add_tail(&entry->entry, &arm_pmus);
+
+	if (list_is_singular(&arm_pmus))
 		static_branch_enable(&kvm_arm_pmu_available);
+
+out_unlock:
+	mutex_unlock(&arm_pmus_lock);
 }
 
 static struct arm_pmu *kvm_pmu_probe_armpmu(void)

include/kvm/arm_pmu.h

@@ -29,6 +29,11 @@ struct kvm_pmu {
 	struct irq_work overflow_work;
 };
 
+struct arm_pmu_entry {
+	struct list_head entry;
+	struct arm_pmu *arm_pmu;
+};
+
 DECLARE_STATIC_KEY_FALSE(kvm_arm_pmu_available);
 
 static __always_inline bool kvm_arm_support_pmu_v3(void)