kvm-vfio: Decouple only when we match a group

commit e323369b upstream.

Unset-KVM and decrement-assignment only when we find the group in our
list.  Otherwise we can get out of sync if the user triggers this for
groups that aren't currently on our list.
Signed-off-by: Alex Williamson <alex.williamson@redhat.com>
Reviewed-by: Alexey Kardashevskiy <aik@ozlabs.ru>
Reviewed-by: Eric Auger <eric.auger@redhat.com>
Tested-by: Eric Auger <eric.auger@redhat.com>
Acked-by: Paolo Bonzini <pbonzini@redhat.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

virt/kvm/vfio.c

@@ -246,21 +246,20 @@ static int kvm_vfio_set_group(struct kvm_device *dev, long attr, u64 arg)
 				continue;
 
 			list_del(&kvg->node);
+			kvm_arch_end_assignment(dev->kvm);
+#ifdef CONFIG_SPAPR_TCE_IOMMU
+			kvm_spapr_tce_release_vfio_group(dev->kvm,
+							 kvg->vfio_group);
+#endif
+			kvm_vfio_group_set_kvm(kvg->vfio_group, NULL);
 			kvm_vfio_group_put_external_user(kvg->vfio_group);
 			kfree(kvg);
 			ret = 0;
 			break;
 		}
 
-		kvm_arch_end_assignment(dev->kvm);
-
 		mutex_unlock(&kv->lock);
 
-#ifdef CONFIG_SPAPR_TCE_IOMMU
-		kvm_spapr_tce_release_vfio_group(dev->kvm, vfio_group);
-#endif
-		kvm_vfio_group_set_kvm(vfio_group, NULL);
-
 		kvm_vfio_group_put_external_user(vfio_group);
 
 		kvm_vfio_update_coherency(dev);