KVM: Avoid calling smp_call_function_single() with interrupts disabled

When taking a cpu down, we need to hardware_disable() it.
Unfortunately, the CPU_DYING notifier is called with interrupts
disabled, which means we can't use smp_call_function_single().

Fortunately, the CPU_DYING notifier is always called on the dying cpu,
so we don't need to use the function at all and can simply call
hardware_disable() directly.
Tested-by: NPaolo Ornati <ornati@fastwebnet.it>
Signed-off-by: NAvi Kivity <avi@qumranet.com>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>

drivers/kvm/kvm_main.c

@@ -2974,6 +2974,10 @@ static int kvm_cpu_hotplug(struct notifier_block *notifier, unsigned long val,
 	switch (val) {
 	case CPU_DYING:
 	case CPU_DYING_FROZEN:
+		printk(KERN_INFO "kvm: disabling virtualization on CPU%d\n",
+		       cpu);
+		hardware_disable(NULL);
+		break;
 	case CPU_UP_CANCELED:
 	case CPU_UP_CANCELED_FROZEN:
 		printk(KERN_INFO "kvm: disabling virtualization on CPU%d\n",