x86/kvm: Convert to hotplug state machine

Install the callbacks via the state machine. The online & down callbacks are
invoked on the target CPU so we can avoid using smp_call_function_single().
local_irq_disable() is used because smp_call_function_single() used to invoke
the function with interrupts disabled.

Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Reviewed-by: Paolo Bonzini <pbonzini@redhat.com>
Cc: kvm@vger.kernel.org
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Gleb Natapov <gleb@kernel.org>
Cc: rt@linutronix.de
Link: http://lkml.kernel.org/r/20160818125731.27256-15-bigeasy@linutronix.de
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>

arch/x86/kernel/kvm.c

@@ -423,12 +423,7 @@ static void __init kvm_smp_prepare_boot_cpu(void)
 	kvm_spinlock_init();
 }
 
-static void kvm_guest_cpu_online(void *dummy)
-{
-	kvm_guest_cpu_init();
-}
-
-static void kvm_guest_cpu_offline(void *dummy)
+static void kvm_guest_cpu_offline(void)
 {
 	kvm_disable_steal_time();
 	if (kvm_para_has_feature(KVM_FEATURE_PV_EOI))
@@ -437,29 +432,21 @@ static void kvm_guest_cpu_offline(void *dummy)
 	apf_task_wake_all();
 }
 
-static int kvm_cpu_notify(struct notifier_block *self, unsigned long action,
-			  void *hcpu)
+static int kvm_cpu_online(unsigned int cpu)
 {
-	int cpu = (unsigned long)hcpu;
-	switch (action) {
-	case CPU_ONLINE:
-	case CPU_DOWN_FAILED:
-	case CPU_ONLINE_FROZEN:
-		smp_call_function_single(cpu, kvm_guest_cpu_online, NULL, 0);
-		break;
-	case CPU_DOWN_PREPARE:
-	case CPU_DOWN_PREPARE_FROZEN:
-		smp_call_function_single(cpu, kvm_guest_cpu_offline, NULL, 1);
-		break;
-	default:
-		break;
-	}
-	return NOTIFY_OK;
+	local_irq_disable();
+	kvm_guest_cpu_init();
+	local_irq_enable();
+	return 0;
 }
 
-static struct notifier_block kvm_cpu_notifier = {
-        .notifier_call  = kvm_cpu_notify,
-};
+static int kvm_cpu_down_prepare(unsigned int cpu)
+{
+	local_irq_disable();
+	kvm_guest_cpu_offline();
+	local_irq_enable();
+	return 0;
+}
 #endif
 
 static void __init kvm_apf_trap_init(void)
@@ -494,7 +481,9 @@ void __init kvm_guest_init(void)
 
 #ifdef CONFIG_SMP
 	smp_ops.smp_prepare_boot_cpu = kvm_smp_prepare_boot_cpu;
-	register_cpu_notifier(&kvm_cpu_notifier);
+	if (cpuhp_setup_state_nocalls(CPUHP_AP_ONLINE_DYN, "x86/kvm:online",
+				      kvm_cpu_online, kvm_cpu_down_prepare) < 0)
+		pr_err("kvm_guest: Failed to install cpu hotplug callbacks\n");
 #else
 	kvm_guest_cpu_init();
 #endif