KVM: Keep track of which cpus have virtualization enabled

By keeping track of which cpus have virtualization enabled, we
prevent double-enable or double-disable during hotplug, which is a
very fatal oops.
Signed-off-by: Avi Kivity <avi@qumranet.com>

drivers/kvm/kvm_main.c

@@ -50,8 +50,12 @@ MODULE_LICENSE("GPL");
 static DEFINE_SPINLOCK(kvm_lock);
 static LIST_HEAD(vm_list);
 
+static cpumask_t cpus_hardware_enabled;
+
 struct kvm_arch_ops *kvm_arch_ops;
 
+static void hardware_disable(void *ignored);
+
 #define STAT_OFFSET(x) offsetof(struct kvm_vcpu, stat.x)
 
 static struct kvm_stats_debugfs_item {
@@ -2930,7 +2934,7 @@ static int kvm_reboot(struct notifier_block *notifier, unsigned long val,
 		 * in vmx root mode.
 		 */
 		printk(KERN_INFO "kvm: exiting hardware virtualization\n");
-		on_each_cpu(kvm_arch_ops->hardware_disable, NULL, 0, 1);
+		on_each_cpu(hardware_disable, NULL, 0, 1);
 	}
 	return NOTIFY_OK;
 }
@@ -2973,6 +2977,27 @@ static void decache_vcpus_on_cpu(int cpu)
 	spin_unlock(&kvm_lock);
 }
 
+static void hardware_enable(void *junk)
+{
+	int cpu = raw_smp_processor_id();
+
+	if (cpu_isset(cpu, cpus_hardware_enabled))
+		return;
+	cpu_set(cpu, cpus_hardware_enabled);
+	kvm_arch_ops->hardware_enable(NULL);
+}
+
+static void hardware_disable(void *junk)
+{
+	int cpu = raw_smp_processor_id();
+
+	if (!cpu_isset(cpu, cpus_hardware_enabled))
+		return;
+	cpu_clear(cpu, cpus_hardware_enabled);
+	decache_vcpus_on_cpu(cpu);
+	kvm_arch_ops->hardware_disable(NULL);
+}
+
 static int kvm_cpu_hotplug(struct notifier_block *notifier, unsigned long val,
 			   void *v)
 {
@@ -2985,16 +3010,13 @@ static int kvm_cpu_hotplug(struct notifier_block *notifier, unsigned long val,
 	case CPU_UP_CANCELED_FROZEN:
 		printk(KERN_INFO "kvm: disabling virtualization on CPU%d\n",
 		       cpu);
-		decache_vcpus_on_cpu(cpu);
-		smp_call_function_single(cpu, kvm_arch_ops->hardware_disable,
-					 NULL, 0, 1);
+		smp_call_function_single(cpu, hardware_disable, NULL, 0, 1);
 		break;
 	case CPU_ONLINE:
 	case CPU_ONLINE_FROZEN:
 		printk(KERN_INFO "kvm: enabling virtualization on CPU%d\n",
 		       cpu);
-		smp_call_function_single(cpu, kvm_arch_ops->hardware_enable,
-					 NULL, 0, 1);
+		smp_call_function_single(cpu, hardware_enable, NULL, 0, 1);
 		break;
 	}
 	return NOTIFY_OK;
@@ -3088,14 +3110,13 @@ static void kvm_exit_debug(void)
 
 static int kvm_suspend(struct sys_device *dev, pm_message_t state)
 {
-	decache_vcpus_on_cpu(raw_smp_processor_id());
-	on_each_cpu(kvm_arch_ops->hardware_disable, NULL, 0, 1);
+	on_each_cpu(hardware_disable, NULL, 0, 0);
 	return 0;
 }
 
 static int kvm_resume(struct sys_device *dev)
 {
-	on_each_cpu(kvm_arch_ops->hardware_enable, NULL, 0, 1);
+	on_each_cpu(hardware_disable, NULL, 0, 0);
 	return 0;
 }
 
@@ -3136,7 +3157,7 @@ int kvm_init_arch(struct kvm_arch_ops *ops, struct module *module)
 	if (r < 0)
 		goto out;
 
-	on_each_cpu(kvm_arch_ops->hardware_enable, NULL, 0, 1);
+	on_each_cpu(hardware_enable, NULL, 0, 1);
 	r = register_cpu_notifier(&kvm_cpu_notifier);
 	if (r)
 		goto out_free_1;
@@ -3168,7 +3189,7 @@ int kvm_init_arch(struct kvm_arch_ops *ops, struct module *module)
 	unregister_reboot_notifier(&kvm_reboot_notifier);
 	unregister_cpu_notifier(&kvm_cpu_notifier);
 out_free_1:
-	on_each_cpu(kvm_arch_ops->hardware_disable, NULL, 0, 1);
+	on_each_cpu(hardware_disable, NULL, 0, 1);
 	kvm_arch_ops->hardware_unsetup();
 out:
 	kvm_arch_ops = NULL;
@@ -3182,7 +3203,7 @@ void kvm_exit_arch(void)
 	sysdev_class_unregister(&kvm_sysdev_class);
 	unregister_reboot_notifier(&kvm_reboot_notifier);
 	unregister_cpu_notifier(&kvm_cpu_notifier);
-	on_each_cpu(kvm_arch_ops->hardware_disable, NULL, 0, 1);
+	on_each_cpu(hardware_disable, NULL, 0, 1);
 	kvm_arch_ops->hardware_unsetup();
 	kvm_arch_ops = NULL;
 }