[PATCH 3/8] KVM: Initialize kvm_arch_ops on unload

[Avi Kivity <avi-atKUWr5tajBWk0Htik3J/w@public.gmane.org>]

From: Yoshimi Ichiyanagi <ichiyanagi.yoshimi-Zyj7fXuS5i5L9jVzuh4AOg@public.gmane.org>

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 <avi-atKUWr5tajBWk0Htik3J/w@public.gmane.org>

Index: linux-2.6/drivers/kvm/kvm_main.c
===================================================================
--- linux-2.6.orig/drivers/kvm/kvm_main.c
+++ linux-2.6/drivers/kvm/kvm_main.c
@@ -1865,6 +1865,11 @@ int kvm_init_arch(struct kvm_arch_ops *o
 {
 	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()) {
@@ -1907,6 +1912,7 @@ void kvm_exit_arch(void)
 	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)

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