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>

arch/ia64/kvm/kvm-ia64.c

@@ -1337,6 +1337,10 @@ static void kvm_release_vm_pages(struct kvm *kvm)
 	}
 }
 
+void kvm_arch_sync_events(struct kvm *kvm)
+{
+}
+
 void kvm_arch_destroy_vm(struct kvm *kvm)
 {
 	kvm_iommu_unmap_guest(kvm);

arch/powerpc/kvm/powerpc.c

@@ -125,6 +125,10 @@ static void kvmppc_free_vcpus(struct kvm *kvm)
 	}
 }
 
+void kvm_arch_sync_events(struct kvm *kvm)
+{
+}
+
 void kvm_arch_destroy_vm(struct kvm *kvm)
 {
 	kvmppc_free_vcpus(kvm);

arch/s390/kvm/kvm-s390.c

@@ -212,6 +212,10 @@ static void kvm_free_vcpus(struct kvm *kvm)
 	}
 }
 
+void kvm_arch_sync_events(struct kvm *kvm)
+{
+}
+
 void kvm_arch_destroy_vm(struct kvm *kvm)
 {
 	kvm_free_vcpus(kvm);

arch/x86/kvm/x86.c

@@ -4127,6 +4127,10 @@ static void kvm_free_vcpus(struct kvm *kvm)
 
 }
 
+void kvm_arch_sync_events(struct kvm *kvm)
+{
+}
+
 void kvm_arch_destroy_vm(struct kvm *kvm)
 {
 	kvm_free_all_assigned_devices(kvm);

include/linux/kvm_host.h

@@ -285,6 +285,7 @@ void kvm_free_physmem(struct kvm *kvm);
 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);

virt/kvm/kvm_main.c

@@ -891,6 +891,7 @@ static void kvm_destroy_vm(struct kvm *kvm)
 {
 	struct mm_struct *mm = kvm->mm;
 
+	kvm_arch_sync_events(kvm);
 	spin_lock(&kvm_lock);
 	list_del(&kvm->vm_list);
 	spin_unlock(&kvm_lock);