x86/microcode: Convert to hotplug state machine

Install the callbacks via the state machine. 
CPU_UP_CANCELED_FROZEN() is not preserved: It is only there to free memory in an
error case because it is assumed if the CPU does show up on resume it won't be
seen ever again. As per Borislav:
|IOW, you don't need mc_cpu_dead().

Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Borislav Petkov <bp@alien8.de>
Cc: rt@linutronix.de
Link: http://lkml.kernel.org/r/20160907164523.46a2xnffha4bv63g@linutronix.de
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>

arch/x86/kernel/cpu/microcode/core.c

@@ -558,55 +558,36 @@ static struct syscore_ops mc_syscore_ops = {
 	.resume			= mc_bp_resume,
 };
 
-static int
-mc_cpu_callback(struct notifier_block *nb, unsigned long action, void *hcpu)
+static int mc_cpu_online(unsigned int cpu)
 {
-	unsigned int cpu = (unsigned long)hcpu;
 	struct device *dev;
 
 	dev = get_cpu_device(cpu);
+	microcode_update_cpu(cpu);
+	pr_debug("CPU%d added\n", cpu);
 
-	switch (action & ~CPU_TASKS_FROZEN) {
-	case CPU_ONLINE:
-		microcode_update_cpu(cpu);
-		pr_debug("CPU%d added\n", cpu);
-		/*
-		 * "break" is missing on purpose here because we want to fall
-		 * through in order to create the sysfs group.
-		 */
-
-	case CPU_DOWN_FAILED:
-		if (sysfs_create_group(&dev->kobj, &mc_attr_group))
-			pr_err("Failed to create group for CPU%d\n", cpu);
-		break;
+	if (sysfs_create_group(&dev->kobj, &mc_attr_group))
+		pr_err("Failed to create group for CPU%d\n", cpu);
+	return 0;
+}
 
-	case CPU_DOWN_PREPARE:
-		/* Suspend is in progress, only remove the interface */
-		sysfs_remove_group(&dev->kobj, &mc_attr_group);
-		pr_debug("CPU%d removed\n", cpu);
-		break;
+static int mc_cpu_down_prep(unsigned int cpu)
+{
+	struct device *dev;
 
+	dev = get_cpu_device(cpu);
+	/* Suspend is in progress, only remove the interface */
+	sysfs_remove_group(&dev->kobj, &mc_attr_group);
+	pr_debug("CPU%d removed\n", cpu);
 	/*
-	 * case CPU_DEAD:
-	 *
 	 * When a CPU goes offline, don't free up or invalidate the copy of
 	 * the microcode in kernel memory, so that we can reuse it when the
 	 * CPU comes back online without unnecessarily requesting the userspace
 	 * for it again.
 	 */
-	}
-
-	/* The CPU refused to come up during a system resume */
-	if (action == CPU_UP_CANCELED_FROZEN)
-		microcode_fini_cpu(cpu);
-
-	return NOTIFY_OK;
+	return 0;
 }
 
-static struct notifier_block mc_cpu_notifier = {
-	.notifier_call	= mc_cpu_callback,
-};
-
 static struct attribute *cpu_root_microcode_attrs[] = {
 	&dev_attr_reload.attr,
 	NULL
@@ -665,7 +646,8 @@ int __init microcode_init(void)
 		goto out_ucode_group;
 
 	register_syscore_ops(&mc_syscore_ops);
-	register_hotcpu_notifier(&mc_cpu_notifier);
+	cpuhp_setup_state_nocalls(CPUHP_AP_ONLINE_DYN, "x86/microcode:online",
+				  mc_cpu_online, mc_cpu_down_prep);
 
 	pr_info("Microcode Update Driver: v" MICROCODE_VERSION
 		" <tigran@aivazian.fsnet.co.uk>, Peter Oruba\n");