target/arm/cpu: Ensure we can use the pmu with kvm

We first convert the pmu property from a static property to one with
its own accessors. Then we use the set accessor to check if the PMU is
supported when using KVM. Indeed a 32-bit KVM host does not support
the PMU, so this check will catch an attempt to use it at property-set
time.
Signed-off-by: NAndrew Jones <drjones@redhat.com>
Reviewed-by: NEric Auger <eric.auger@redhat.com>
Signed-off-by: NPeter Maydell <peter.maydell@linaro.org>

target/arm/cpu.c

@@ -994,10 +994,6 @@ static Property arm_cpu_has_el3_property =
 static Property arm_cpu_cfgend_property =
             DEFINE_PROP_BOOL("cfgend", ARMCPU, cfgend, false);
 
-/* use property name "pmu" to match other archs and virt tools */
-static Property arm_cpu_has_pmu_property =
-            DEFINE_PROP_BOOL("pmu", ARMCPU, has_pmu, true);
-
 static Property arm_cpu_has_vfp_property =
             DEFINE_PROP_BOOL("vfp", ARMCPU, has_vfp, true);
 
@@ -1020,6 +1016,29 @@ static Property arm_cpu_pmsav7_dregion_property =
                                            pmsav7_dregion,
                                            qdev_prop_uint32, uint32_t);
 
+static bool arm_get_pmu(Object *obj, Error **errp)
+{
+    ARMCPU *cpu = ARM_CPU(obj);
+
+    return cpu->has_pmu;
+}
+
+static void arm_set_pmu(Object *obj, bool value, Error **errp)
+{
+    ARMCPU *cpu = ARM_CPU(obj);
+
+    if (value) {
+        if (kvm_enabled() && !kvm_arm_pmu_supported(CPU(cpu))) {
+            error_setg(errp, "'pmu' feature not supported by KVM on this host");
+            return;
+        }
+        set_feature(&cpu->env, ARM_FEATURE_PMU);
+    } else {
+        unset_feature(&cpu->env, ARM_FEATURE_PMU);
+    }
+    cpu->has_pmu = value;
+}
+
 static void arm_get_init_svtor(Object *obj, Visitor *v, const char *name,
                                void *opaque, Error **errp)
 {
@@ -1094,7 +1113,8 @@ void arm_cpu_post_init(Object *obj)
     }
 
     if (arm_feature(&cpu->env, ARM_FEATURE_PMU)) {
-        qdev_property_add_static(DEVICE(obj), &arm_cpu_has_pmu_property,
+        cpu->has_pmu = true;
+        object_property_add_bool(obj, "pmu", arm_get_pmu, arm_set_pmu,
                                  &error_abort);
     }
 

target/arm/kvm.c

@@ -162,6 +162,13 @@ void kvm_arm_set_cpu_features_from_host(ARMCPU *cpu)
     env->features = arm_host_cpu_features.features;
 }
 
+bool kvm_arm_pmu_supported(CPUState *cpu)
+{
+    KVMState *s = KVM_STATE(current_machine->accelerator);
+
+    return kvm_check_extension(s, KVM_CAP_ARM_PMU_V3);
+}
+
 int kvm_arm_get_max_vm_ipa_size(MachineState *ms)
 {
     KVMState *s = KVM_STATE(ms->accelerator);

target/arm/kvm_arm.h

@@ -216,6 +216,15 @@ void kvm_arm_set_cpu_features_from_host(ARMCPU *cpu);
  */
 bool kvm_arm_aarch32_supported(CPUState *cs);
 
+/**
+ * bool kvm_arm_pmu_supported:
+ * @cs: CPUState
+ *
+ * Returns: true if the KVM VCPU can enable its PMU
+ * and false otherwise.
+ */
+bool kvm_arm_pmu_supported(CPUState *cs);
+
 /**
  * kvm_arm_get_max_vm_ipa_size - Returns the number of bits in the
  * IPA address space supported by KVM
@@ -261,6 +270,11 @@ static inline bool kvm_arm_aarch32_supported(CPUState *cs)
     return false;
 }
 
+static inline bool kvm_arm_pmu_supported(CPUState *cs)
+{
+    return false;
+}
+
 static inline int kvm_arm_get_max_vm_ipa_size(MachineState *ms)
 {
     return -ENOENT;