On Mon, Jul 24, 2023 at 02:22:05PM -0300, Jason Gunthorpe wrote:

-void __init iommufd_test_init(void)
+int __init iommufd_test_init(void)
 {
+	struct platform_device_info pdevinfo = {
+		.name = "iommufd_selftest_iommu",
+	};
+	int rc;
+
 	dbgfs_root =
 		fault_create_debugfs_attr("fail_iommufd", NULL, &fail_iommufd);
-	WARN_ON(bus_register(&iommufd_mock_bus_type));
+
+	selftest_iommu_dev = platform_device_register_full(&pdevinfo);
+	if (IS_ERR(selftest_iommu_dev)) {
+		rc = PTR_ERR(selftest_iommu_dev);
+		goto err_dbgfs;
+	}
+
+	rc = bus_register(&iommufd_mock_bus_type.bus);
+	if (rc)
+		goto err_platform;
+
+	mock_iommu_device.dev = &selftest_iommu_dev->dev;
+	rc = iommu_device_register_bus(&mock_iommu_device, &mock_ops,
+				  &iommufd_mock_bus_type.bus,
+				  &iommufd_mock_bus_type.nb);
+	if (rc)
+		goto err_bus;
+	return 0;
+
+err_bus:
+	bus_unregister(&iommufd_mock_bus_type.bus);
+err_platform:
+	platform_device_del(selftest_iommu_dev);
+err_dbgfs:
+	debugfs_remove_recursive(dbgfs_root);
+	return rc;
 }
 
 void iommufd_test_exit(void)
 {
+	iommu_device_unregister_bus(&mock_iommu_device,
+				    &iommufd_mock_bus_type.bus,
+				    &iommufd_mock_bus_type.nb);
+	bus_unregister(&iommufd_mock_bus_type.bus);
+	platform_device_del(selftest_iommu_dev);
 	debugfs_remove_recursive(dbgfs_root);
-	bus_unregister(&iommufd_mock_bus_type);
 }

There is a mistake here that started to become visible after one of
the rebases, it needs to call iommu_device_sysfs_add() prior to
iommu_device_register_bus() otherwise the iommu core stuff does not
fully initialize and weird stuff starts happening.

So, it needs this:

diff --git a/drivers/iommu/iommufd/selftest.c b/drivers/iommu/iommufd/selftest.c
index 5433c9c545526d..d2b59a1157441c 100644
--- a/drivers/iommu/iommufd/selftest.c
+++ b/drivers/iommu/iommufd/selftest.c

@@ -987,14 +987,21 @@ int __init iommufd_test_init(void)
 	if (rc)
 		goto err_platform;
 
-	mock_iommu_device.dev = &selftest_iommu_dev->dev;
+	rc = iommu_device_sysfs_add(&mock_iommu_device,
+				    &selftest_iommu_dev->dev, NULL, "%s",
+				    dev_name(&selftest_iommu_dev->dev));
+	if (rc)
+		goto err_bus;
+
 	rc = iommu_device_register_bus(&mock_iommu_device, &mock_ops,
 				  &iommufd_mock_bus_type.bus,
 				  &iommufd_mock_bus_type.nb);
 	if (rc)
-		goto err_bus;
+		goto err_sysfs;
 	return 0;
 
+err_sysfs:
+	iommu_device_sysfs_remove(&mock_iommu_device);
 err_bus:
 	bus_unregister(&iommufd_mock_bus_type.bus);
 err_platform:

@@ -1006,6 +1013,7 @@ int __init iommufd_test_init(void)
 
 void iommufd_test_exit(void)
 {
+	iommu_device_sysfs_remove(&mock_iommu_device);
 	iommu_device_unregister_bus(&mock_iommu_device,
 				    &iommufd_mock_bus_type.bus,
 				    &iommufd_mock_bus_type.nb);