KVM: Explicity initialize cpus_hardware_enabled

Under CONFIG_MAXSMP, cpus_hardware_enabled is allocated from the heap and
not statically initialized.  This causes a crash on reboot when kvm thinks
vmx is enabled on random nonexistent cpus and accesses nonexistent percpu
lists.

Fix by explicitly clearing the variable.

Cc: stable@kernel.org
Reported-and-tested-by: Yinghai Lu <yinghai@kernel.org>
Signed-off-by: Avi Kivity <avi@redhat.com>

virt/kvm/kvm_main.c

@@ -2305,6 +2305,7 @@ int kvm_init(void *opaque, unsigned int vcpu_size,
 		r = -ENOMEM;
 		goto out_free_0;
 	}
+	cpumask_clear(cpus_hardware_enabled);
 
 	r = kvm_arch_hardware_setup();
 	if (r < 0)