x86/smp: Replace cpu_up/down() with add/remove_cpu()

The core device API performs extra housekeeping bits that are missing
from directly calling cpu_up/down().

See commit a6717c01 ("powerpc/rtas: use device model APIs and
serialization during LPM") for an example description of what might go
wrong.

This also prepares to make cpu_up/down() a private interface of the CPU
subsystem.
Signed-off-by: Qais Yousef <qais.yousef@arm.com>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Link: https://lkml.kernel.org/r/20200323135110.30522-10-qais.yousef@arm.com

arch/x86/kernel/topology.c

@@ -59,39 +59,29 @@ __setup("cpu0_hotplug", enable_cpu0_hotplug);
  */
 int _debug_hotplug_cpu(int cpu, int action)
 {
-	struct device *dev = get_cpu_device(cpu);
 	int ret;
 
 	if (!cpu_is_hotpluggable(cpu))
 		return -EINVAL;
 
-	lock_device_hotplug();
-
 	switch (action) {
 	case 0:
-		ret = cpu_down(cpu);
-		if (!ret) {
+		ret = remove_cpu(cpu);
+		if (!ret)
 			pr_info("DEBUG_HOTPLUG_CPU0: CPU %u is now offline\n", cpu);
-			dev->offline = true;
-			kobject_uevent(&dev->kobj, KOBJ_OFFLINE);
-		} else
+		else
 			pr_debug("Can't offline CPU%d.\n", cpu);
 		break;
 	case 1:
-		ret = cpu_up(cpu);
-		if (!ret) {
-			dev->offline = false;
-			kobject_uevent(&dev->kobj, KOBJ_ONLINE);
-		} else {
+		ret = add_cpu(cpu);
+		if (ret)
 			pr_debug("Can't online CPU%d.\n", cpu);
-		}
+
 		break;
 	default:
 		ret = -EINVAL;
 	}
 
-	unlock_device_hotplug();
-
 	return ret;
 }
 

arch/x86/mm/mmio-mod.c

@@ -386,7 +386,7 @@ static void enter_uniprocessor(void)
 	put_online_cpus();
 
 	for_each_cpu(cpu, downed_cpus) {
-		err = cpu_down(cpu);
+		err = remove_cpu(cpu);
 		if (!err)
 			pr_info("CPU%d is down.\n", cpu);
 		else
@@ -406,7 +406,7 @@ static void leave_uniprocessor(void)
 		return;
 	pr_notice("Re-enabling CPUs...\n");
 	for_each_cpu(cpu, downed_cpus) {
-		err = cpu_up(cpu);
+		err = add_cpu(cpu);
 		if (!err)
 			pr_info("enabled CPU%d.\n", cpu);
 		else

arch/x86/xen/smp.c

@@ -132,7 +132,7 @@ void __init xen_smp_cpus_done(unsigned int max_cpus)
 		if (xen_vcpu_nr(cpu) < MAX_VIRT_CPUS)
 			continue;
 
-		rc = cpu_down(cpu);
+		rc = remove_cpu(cpu);
 
 		if (rc == 0) {
 			/*