iommufd: Register iommufd mock devices with fwspec

Since the bus ops were retired the iommu subsystem changed to using fwspec
to match the iommu driver to the iommu device. If a device has a NULL
fwspec then it is matched to the first iommu driver with a NULL fwspec,
effectively disabling support for systems with more than one non-fwspec
iommu driver.

Thus, if the iommufd selfest are run in an x86 system that registers a
non-fwspec iommu driver they fail to bind their mock devices to the mock
iommu driver.

Fix this by allocating a software fwnode for mock iommu driver's
iommu_device, and set it to the device which mock iommu driver created.

This is done by adding a new helper iommu_mock_device_add() which abuses
the internals of the fwspec system to establish a fwspec before the device
is added and is careful not to leak it. A matching dummy fwspec is
automatically added to the mock iommu driver.

Test by "make -C toosl/testing/selftests TARGETS=iommu run_tests":
PASSED: 229 / 229 tests passed.

In addition, this issue is also can be found on amd platform, and
also tested on a amd machine.

Link: https://patch.msgid.link/r/20250925054730.3877-1-kanie@linux.alibaba.com
Fixes: 17de3f5fdd35 ("iommu: Retire bus ops")
Signed-off-by: Guixin Liu <kanie@linux.alibaba.com>
Reviewed-by: Lu Baolu <baolu.lu@linux.intel.com>
Tested-by: Qinyun Tan <qinyuntan@linux.alibaba.com>
Signed-off-by: Jason Gunthorpe <jgg@nvidia.com>

3 files changed, 29 insertions, 1 deletions

diff --git a/drivers/iommu/iommu-priv.h b/drivers/iommu/iommu-priv.h
index e236b932e766..c95394cd03a7 100644
--- a/drivers/iommu/iommu-priv.h
+++ b/drivers/iommu/iommu-priv.h
@@ -37,6 +37,8 @@ void iommu_device_unregister_bus(struct iommu_device *iommu,
 				 const struct bus_type *bus,
 				 struct notifier_block *nb);
 
+int iommu_mock_device_add(struct device *dev, struct iommu_device *iommu);
+
 struct iommu_attach_handle *iommu_attach_handle_get(struct iommu_group *group,
 						    ioasid_t pasid,
 						    unsigned int type);
diff --git a/drivers/iommu/iommu.c b/drivers/iommu/iommu.c
index 060ebe330ee1..59244c744eab 100644
--- a/drivers/iommu/iommu.c
+++ b/drivers/iommu/iommu.c
@@ -304,6 +304,7 @@ void iommu_device_unregister_bus(struct iommu_device *iommu,
 				 struct notifier_block *nb)
 {
 	bus_unregister_notifier(bus, nb);
+	fwnode_remove_software_node(iommu->fwnode);
 	iommu_device_unregister(iommu);
 }
 EXPORT_SYMBOL_GPL(iommu_device_unregister_bus);
@@ -326,6 +327,12 @@ int iommu_device_register_bus(struct iommu_device *iommu,
 	if (err)
 		return err;
 
+	iommu->fwnode = fwnode_create_software_node(NULL, NULL);
+	if (IS_ERR(iommu->fwnode)) {
+		bus_unregister_notifier(bus, nb);
+		return PTR_ERR(iommu->fwnode);
+	}
+
 	spin_lock(&iommu_device_lock);
 	list_add_tail(&iommu->list, &iommu_device_list);
 	spin_unlock(&iommu_device_lock);
@@ -335,9 +342,28 @@ int iommu_device_register_bus(struct iommu_device *iommu,
 		iommu_device_unregister_bus(iommu, bus, nb);
 		return err;
 	}
+	WRITE_ONCE(iommu->ready, true);
 	return 0;
 }
 EXPORT_SYMBOL_GPL(iommu_device_register_bus);
+
+int iommu_mock_device_add(struct device *dev, struct iommu_device *iommu)
+{
+	int rc;
+
+	mutex_lock(&iommu_probe_device_lock);
+	rc = iommu_fwspec_init(dev, iommu->fwnode);
+	mutex_unlock(&iommu_probe_device_lock);
+
+	if (rc)
+		return rc;
+
+	rc = device_add(dev);
+	if (rc)
+		iommu_fwspec_free(dev);
+	return rc;
+}
+EXPORT_SYMBOL_GPL(iommu_mock_device_add);
 #endif
 
 static struct dev_iommu *dev_iommu_get(struct device *dev)
diff --git a/drivers/iommu/iommufd/selftest.c b/drivers/iommu/iommufd/selftest.c
index 61686603c769..de178827a078 100644
--- a/drivers/iommu/iommufd/selftest.c
+++ b/drivers/iommu/iommufd/selftest.c
@@ -1126,7 +1126,7 @@ static struct mock_dev *mock_dev_create(unsigned long dev_flags)
 		goto err_put;
 	}
 
-	rc = device_add(&mdev->dev);
+	rc = iommu_mock_device_add(&mdev->dev, &mock_iommu.iommu_dev);
 	if (rc)
 		goto err_put;
 	return mdev;