iommu: Move bus setup to IOMMU device registration

Move the bus setup to iommu_device_register(). This should allow
bus_iommu_probe() to be correctly replayed for multiple IOMMU instances,
and leaves bus_set_iommu() as a glorified no-op to be cleaned up next.

At this point we can also handle cleanup better than just rolling back
the most-recently-touched bus upon failure - which may release devices
owned by other already-registered instances, and still leave devices on
other buses with dangling pointers to the failed instance. Now it's easy
to clean up the exact footprint of a given instance, no more, no less.
Tested-by: Marek Szyprowski <m.szyprowski@samsung.com>
Reviewed-by: Krishna Reddy <vdumpa@nvidia.com>
Reviewed-by: Kevin Tian <kevin.tian@intel.com>
Tested-by: Matthew Rosato <mjrosato@linux.ibm.com> # s390
Tested-by: Niklas Schnelle <schnelle@linux.ibm.com> # s390
Signed-off-by: Robin Murphy <robin.murphy@arm.com>
Link: https://lore.kernel.org/r/d342b6f27efb5ef3e93aacaa3012d25386d74866.1660572783.git.robin.murphy@arm.comSigned-off-by: Joerg Roedel <jroedel@suse.de>

drivers/iommu/iommu.c

@@ -188,6 +188,14 @@ static int __init iommu_subsys_init(void)
 }
 subsys_initcall(iommu_subsys_init);
 
+static int remove_iommu_group(struct device *dev, void *data)
+{
+	if (dev->iommu && dev->iommu->iommu_dev == data)
+		iommu_release_device(dev);
+
+	return 0;
+}
+
 /**
  * iommu_device_register() - Register an IOMMU hardware instance
  * @iommu: IOMMU handle for the instance
@@ -199,9 +207,18 @@ subsys_initcall(iommu_subsys_init);
 int iommu_device_register(struct iommu_device *iommu,
 			  const struct iommu_ops *ops, struct device *hwdev)
 {
+	int err = 0;
+
 	/* We need to be able to take module references appropriately */
 	if (WARN_ON(is_module_address((unsigned long)ops) && !ops->owner))
 		return -EINVAL;
+	/*
+	 * Temporarily enforce global restriction to a single driver. This was
+	 * already the de-facto behaviour, since any possible combination of
+	 * existing drivers would compete for at least the PCI or platform bus.
+	 */
+	if (iommu_buses[0]->iommu_ops && iommu_buses[0]->iommu_ops != ops)
+		return -EBUSY;
 
 	iommu->ops = ops;
 	if (hwdev)
@@ -210,12 +227,22 @@ int iommu_device_register(struct iommu_device *iommu,
 	spin_lock(&iommu_device_lock);
 	list_add_tail(&iommu->list, &iommu_device_list);
 	spin_unlock(&iommu_device_lock);
-	return 0;
+
+	for (int i = 0; i < ARRAY_SIZE(iommu_buses) && !err; i++) {
+		iommu_buses[i]->iommu_ops = ops;
+		err = bus_iommu_probe(iommu_buses[i]);
+	}
+	if (err)
+		iommu_device_unregister(iommu);
+	return err;
 }
 EXPORT_SYMBOL_GPL(iommu_device_register);
 
 void iommu_device_unregister(struct iommu_device *iommu)
 {
+	for (int i = 0; i < ARRAY_SIZE(iommu_buses); i++)
+		bus_for_each_dev(iommu_buses[i], NULL, iommu, remove_iommu_group);
+
 	spin_lock(&iommu_device_lock);
 	list_del(&iommu->list);
 	spin_unlock(&iommu_device_lock);
@@ -1643,13 +1670,6 @@ static int probe_iommu_group(struct device *dev, void *data)
 	return ret;
 }
 
-static int remove_iommu_group(struct device *dev, void *data)
-{
-	iommu_release_device(dev);
-
-	return 0;
-}
-
 static int iommu_bus_notifier(struct notifier_block *nb,
 			      unsigned long action, void *data)
 {
@@ -1821,27 +1841,12 @@ int bus_iommu_probe(struct bus_type *bus)
  */
 int bus_set_iommu(struct bus_type *bus, const struct iommu_ops *ops)
 {
-	int err;
-
-	if (ops == NULL) {
-		bus->iommu_ops = NULL;
-		return 0;
-	}
-
-	if (bus->iommu_ops != NULL)
+	if (bus->iommu_ops && ops && bus->iommu_ops != ops)
 		return -EBUSY;
 
 	bus->iommu_ops = ops;
 
-	/* Do IOMMU specific setup for this bus-type */
-	err = bus_iommu_probe(bus);
-	if (err) {
-		/* Clean up */
-		bus_for_each_dev(bus, NULL, NULL, remove_iommu_group);
-		bus->iommu_ops = NULL;
-	}
-
-	return err;
+	return 0;
 }
 EXPORT_SYMBOL_GPL(bus_set_iommu);