I've avoided doing this because there is no way to make this happen
without an intrusion into the core code. Up till now this has avoided
needing the core code's probe path with some hackery - but now that
default domains are becoming mandatory it is unavoidable. The core probe
path must be run to set the default_domain, only it can do it. Without
a default domain iommufd can't use the group.

Make it so that iommufd selftest can create a real iommu driver and bind
it only to is own private bus. Add iommu_device_register_bus() as a core
code helper to make this possible. It simply sets the right pointers and
registers the notifier block. The mock driver then works like any normal
driver should, with probe triggered by the bus ops

When the bus->iommu_ops stuff is fully unwound we can probably do better
here and remove this special case.

Remove set_platform_dma_ops from selftest and make it use a BLOCKED
default domain.

Signed-off-by: Jason Gunthorpe<jgg@nvidia.com>
---
  drivers/iommu/iommu-priv.h              |  16 +++
  drivers/iommu/iommu.c                   |  43 +++++++
  drivers/iommu/iommufd/iommufd_private.h |   5 +-
  drivers/iommu/iommufd/main.c            |   8 +-
  drivers/iommu/iommufd/selftest.c        | 149 +++++++++++++-----------
  5 files changed, 152 insertions(+), 69 deletions(-)
  create mode 100644 drivers/iommu/iommu-priv.h

diff --git a/drivers/iommu/iommu-priv.h b/drivers/iommu/iommu-priv.h
new file mode 100644
index 00000000000000..1cbc04b9cf7297
--- /dev/null
+++ b/drivers/iommu/iommu-priv.h

@@ -0,0 +1,16 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+/* Copyright (c) 2023, NVIDIA CORPORATION & AFFILIATES.
+ */
+#ifndef __IOMMU_PRIV_H
+#define __IOMMU_PRIV_H
+
+#include <linux/iommu.h>
+
+int iommu_device_register_bus(struct iommu_device *iommu,
+			      const struct iommu_ops *ops, struct bus_type *bus,
+			      struct notifier_block *nb);
+void iommu_device_unregister_bus(struct iommu_device *iommu,
+				 struct bus_type *bus,
+				 struct notifier_block *nb);
+
+#endif

diff --git a/drivers/iommu/iommu.c b/drivers/iommu/iommu.c
index a1a93990b3a211..7fae866af0db7a 100644
--- a/drivers/iommu/iommu.c
+++ b/drivers/iommu/iommu.c

@@ -36,6 +36,7 @@
  #include "dma-iommu.h"
  
  #include "iommu-sva.h"
+#include "iommu-priv.h"
  
  static struct kset *iommu_group_kset;
  static DEFINE_IDA(iommu_group_ida);

@@ -290,6 +291,48 @@ void iommu_device_unregister(struct iommu_device *iommu)
  }
  EXPORT_SYMBOL_GPL(iommu_device_unregister);
  
+#if IS_ENABLED(CONFIG_IOMMUFD_TEST)
+void iommu_device_unregister_bus(struct iommu_device *iommu,
+				 struct bus_type *bus,
+				 struct notifier_block *nb)
+{
+	bus_unregister_notifier(bus, nb);
+	iommu_device_unregister(iommu);
+}
+EXPORT_SYMBOL_GPL(iommu_device_unregister_bus);
+
+/*
+ * Register an iommu driver against a single bus. This is only used by iommufd
+ * selftest to create a mock iommu driver. The caller must provide
+ * some memory to hold a notifier_block.
+ */
+int iommu_device_register_bus(struct iommu_device *iommu,
+			      const struct iommu_ops *ops, struct bus_type *bus,
+			      struct notifier_block *nb)
+{
+	int err;
+
+	iommu->ops = ops;
+	nb->notifier_call = iommu_bus_notifier;
+	err = bus_register_notifier(bus, nb);
+	if (err)
+		return err;
+
+	spin_lock(&iommu_device_lock);
+	list_add_tail(&iommu->list, &iommu_device_list);
+	spin_unlock(&iommu_device_lock);
+
+	bus->iommu_ops = ops;
+	err = bus_iommu_probe(bus);
+	if (err) {
+		iommu_device_unregister_bus(iommu, bus, nb);
+		return err;
+	}
+	return 0;
+}
+EXPORT_SYMBOL_GPL(iommu_device_register_bus);
+#endif