kvm: set/clear kvm to/from vfio_group when group add/delete

Sometimes users need to be aware when a vfio_group attaches to a
KVM or detaches from it. KVM already calls get/put method from vfio to
manipulate the vfio_group reference, it can notify vfio_group in
a similar way.

Cc: Kirti Wankhede <kwankhede@nvidia.com>
Cc: Xiao Guangrong <guangrong.xiao@linux.intel.com>
Signed-off-by: NJike Song <jike.song@intel.com>
Acked-by: NPaolo Bonzini <pbonzini@redhat.com>
Signed-off-by: NAlex Williamson <alex.williamson@redhat.com>

virt/kvm/vfio.c

@@ -60,6 +60,19 @@ static void kvm_vfio_group_put_external_user(struct vfio_group *vfio_group)
 	symbol_put(vfio_group_put_external_user);
 }
 
+static void kvm_vfio_group_set_kvm(struct vfio_group *group, struct kvm *kvm)
+{
+	void (*fn)(struct vfio_group *, struct kvm *);
+
+	fn = symbol_get(vfio_group_set_kvm);
+	if (!fn)
+		return;
+
+	fn(group, kvm);
+
+	symbol_put(vfio_group_set_kvm);
+}
+
 static bool kvm_vfio_group_is_coherent(struct vfio_group *vfio_group)
 {
 	long (*fn)(struct vfio_group *, unsigned long);
@@ -159,6 +172,8 @@ static int kvm_vfio_set_group(struct kvm_device *dev, long attr, u64 arg)
 
 		mutex_unlock(&kv->lock);
 
+		kvm_vfio_group_set_kvm(vfio_group, dev->kvm);
+
 		kvm_vfio_update_coherency(dev);
 
 		return 0;
@@ -196,6 +211,8 @@ static int kvm_vfio_set_group(struct kvm_device *dev, long attr, u64 arg)
 
 		mutex_unlock(&kv->lock);
 
+		kvm_vfio_group_set_kvm(vfio_group, NULL);
+
 		kvm_vfio_group_put_external_user(vfio_group);
 
 		kvm_vfio_update_coherency(dev);
@@ -240,6 +257,7 @@ static void kvm_vfio_destroy(struct kvm_device *dev)
 	struct kvm_vfio_group *kvg, *tmp;
 
 	list_for_each_entry_safe(kvg, tmp, &kv->group_list, node) {
+		kvm_vfio_group_set_kvm(kvg->vfio_group, NULL);
 		kvm_vfio_group_put_external_user(kvg->vfio_group);
 		list_del(&kvg->node);
 		kfree(kvg);