KVM: Add kvm_arch_sync_events to sync with asynchronize events

kvm_arch_sync_events is introduced to quiet down all other events may happen
contemporary with VM destroy process, like IRQ handler and work struct for
assigned device.

For kvm_arch_sync_events is called at the very beginning of kvm_destroy_vm(), so
the state of KVM here is legal and can provide a environment to quiet down other
events.

Signed-off-by: Sheng Yang <sheng@linux.intel.com>
Signed-off-by: Avi Kivity <avi@redhat.com>
diff --git a/include/linux/kvm_host.h b/include/linux/kvm_host.h
index ec49d0b..bf6f703 100644
--- a/include/linux/kvm_host.h
+++ b/include/linux/kvm_host.h
@@ -285,6 +285,7 @@
 struct  kvm *kvm_arch_create_vm(void);
 void kvm_arch_destroy_vm(struct kvm *kvm);
 void kvm_free_all_assigned_devices(struct kvm *kvm);
+void kvm_arch_sync_events(struct kvm *kvm);
 
 int kvm_cpu_get_interrupt(struct kvm_vcpu *v);
 int kvm_cpu_has_interrupt(struct kvm_vcpu *v);