[PATCH] KVM: Initialize kvm_arch_ops on unload

The latest version of kvm doesn't initialize kvm_arch_ops in kvm_init(), which
causes an error with the following sequence.

1. Load the supported arch's module.
2. Load the unsupported arch's module.$B!!(B(loading error)
3. Unload the unsupported arch's module.

You'll get the following error message after step 3. "BUG: unable to handle
to handle kernel paging request at virtual address xxxxxxxx"

The problem here is that the unsupported arch's module overwrites kvm_arch_ops
of the supported arch's module at step 2.

This patch initializes kvm_arch_ops upon loading architecture specific kvm
module, and prevents overwriting kvm_arch_ops when kvm_arch_ops is already set
correctly.

Signed-off-by: Avi Kivity <[e-mail]>
Signed-off-by: Andrew Morton <[e-mail]>
Signed-off-by: Linus Torvalds <[e-mail]>

drivers/kvm/kvm_main.c

···
 {
 	int r;
 
+	if (kvm_arch_ops) {
+		printk(KERN_ERR "kvm: already loaded the other module\n");
+		return -EEXIST;
+	}
+
 	kvm_arch_ops = ops;
 
 	if (!kvm_arch_ops->cpu_has_kvm_support()) {
···
 	unregister_reboot_notifier(&kvm_reboot_notifier);
 	on_each_cpu(kvm_arch_ops->hardware_disable, 0, 0, 1);
 	kvm_arch_ops->hardware_unsetup();
+	kvm_arch_ops = NULL;
 }
 
 static __init int kvm_init(void)