[PATCH] iommu: Add bus_unset_iommu()

[Jean-Philippe Brucker]

Let modular IOMMU drivers undo bus_set_iommu(). Keep track of bus
registrations with a list and refcount, and remove the iommu_ops from
the bus when there are no IOMMU providers anymore.

Signed-off-by: Jean-Philippe Brucker <jean-philippe@xxxxxxxxxx>
---
 drivers/iommu/iommu.c | 101 ++++++++++++++++++++++++++++++++++--------
 include/linux/iommu.h |   1 +
 2 files changed, 84 insertions(+), 18 deletions(-)

diff --git a/drivers/iommu/iommu.c b/drivers/iommu/iommu.c
index 393a5376d7c6..f9bac5633f2a 100644
--- a/drivers/iommu/iommu.c
+++ b/drivers/iommu/iommu.c
@@ -31,6 +31,9 @@ static unsigned int iommu_def_domain_type __read_mostly;
 static bool iommu_dma_strict __read_mostly = true;
 static u32 iommu_cmd_line __read_mostly;
 
+static DEFINE_MUTEX(iommu_bus_notifiers_lock);
+static LIST_HEAD(iommu_bus_notifiers);
+
 struct iommu_group {
 	struct kobject kobj;
 	struct kobject *devices_kobj;
@@ -58,6 +61,14 @@ struct iommu_group_attribute {
 			 const char *buf, size_t count);
 };
 
+struct iommu_bus_notifier {
+	struct notifier_block	nb;
+	const struct iommu_ops	*ops;
+	struct bus_type		*bus;
+	struct list_head	list;
+	refcount_t		refs;
+};
+
 static const char * const iommu_group_resv_type_string[] = {
 	[IOMMU_RESV_DIRECT]			= "direct",
 	[IOMMU_RESV_DIRECT_RELAXABLE]		= "direct-relaxable",
@@ -1494,15 +1505,29 @@ static int iommu_bus_notifier(struct notifier_block *nb,
 static int iommu_bus_init(struct bus_type *bus, const struct iommu_ops *ops)
 {
 	int err;
-	struct notifier_block *nb;
+	struct iommu_bus_notifier *iommu_notifier;
 
-	nb = kzalloc(sizeof(struct notifier_block), GFP_KERNEL);
-	if (!nb)
-		return -ENOMEM;
+	list_for_each_entry(iommu_notifier, &iommu_bus_notifiers, list) {
+		if (iommu_notifier->ops == ops && iommu_notifier->bus == bus) {
+			refcount_inc(&iommu_notifier->refs);
+			return 0;
+		}
+	}
+
+	bus->iommu_ops = ops;
+
+	iommu_notifier = kzalloc(sizeof(*iommu_notifier), GFP_KERNEL);
+	if (!iommu_notifier) {
+		err = -ENOMEM;
+		goto out_clear;
+	}
 
-	nb->notifier_call = iommu_bus_notifier;
+	iommu_notifier->ops = ops;
+	iommu_notifier->bus = bus;
+	iommu_notifier->nb.notifier_call = iommu_bus_notifier;
+	refcount_set(&iommu_notifier->refs, 1);
 
-	err = bus_register_notifier(bus, nb);
+	err = bus_register_notifier(bus, &iommu_notifier->nb);
 	if (err)
 		goto out_free;
 
@@ -1510,20 +1535,47 @@ static int iommu_bus_init(struct bus_type *bus, const struct iommu_ops *ops)
 	if (err)
 		goto out_err;
 
-
+	list_add(&iommu_notifier->list, &iommu_bus_notifiers);
 	return 0;
 
 out_err:
 	/* Clean up */
 	bus_for_each_dev(bus, NULL, NULL, remove_iommu_group);
-	bus_unregister_notifier(bus, nb);
-
+	bus_unregister_notifier(bus, &iommu_notifier->nb);
 out_free:
-	kfree(nb);
+	kfree(iommu_notifier);
+out_clear:
+	bus->iommu_ops = NULL;
 
 	return err;
 }
 
+static int iommu_bus_remove(struct bus_type *bus, const struct iommu_ops *ops)
+{
+	struct iommu_bus_notifier *tmp;
+	struct iommu_bus_notifier *iommu_notifier = NULL;
+
+	list_for_each_entry(tmp, &iommu_bus_notifiers, list) {
+		if (tmp->ops == ops && tmp->bus == bus) {
+			iommu_notifier = tmp;
+			break;
+		}
+	}
+
+	if (!iommu_notifier)
+		return -ESRCH;
+
+	if (!refcount_dec_and_test(&iommu_notifier->refs))
+		return 0;
+
+	list_del(&iommu_notifier->list);
+	bus_for_each_dev(bus, NULL, NULL, remove_iommu_group);
+	bus_unregister_notifier(bus, &iommu_notifier->nb);
+	kfree(iommu_notifier);
+	bus->iommu_ops = NULL;
+	return 0;
+}
+
 /**
  * bus_set_iommu - set iommu-callbacks for the bus
  * @bus: bus.
@@ -1541,20 +1593,33 @@ int bus_set_iommu(struct bus_type *bus, const struct iommu_ops *ops)
 {
 	int err;
 
-	if (bus->iommu_ops != NULL)
-		return -EBUSY;
-
-	bus->iommu_ops = ops;
-
 	/* Do IOMMU specific setup for this bus-type */
-	err = iommu_bus_init(bus, ops);
-	if (err)
-		bus->iommu_ops = NULL;
+	mutex_lock(&iommu_bus_notifiers_lock);
+	if (bus->iommu_ops != NULL && bus->iommu_ops != ops)
+		err = -EBUSY;
+	else
+		err = iommu_bus_init(bus, ops);
+	mutex_unlock(&iommu_bus_notifiers_lock);
 
 	return err;
 }
 EXPORT_SYMBOL_GPL(bus_set_iommu);
 
+int bus_unset_iommu(struct bus_type *bus, const struct iommu_ops *ops)
+{
+	int err;
+
+	mutex_lock(&iommu_bus_notifiers_lock);
+	if (bus->iommu_ops != ops)
+		err = -EINVAL;
+	else
+		err = iommu_bus_remove(bus, ops);
+	mutex_unlock(&iommu_bus_notifiers_lock);
+
+	return err;
+}
+EXPORT_SYMBOL_GPL(bus_unset_iommu);
+
 bool iommu_present(struct bus_type *bus)
 {
 	return bus->iommu_ops != NULL;
diff --git a/include/linux/iommu.h b/include/linux/iommu.h
index 29bac5345563..15c9115e31ff 100644
--- a/include/linux/iommu.h
+++ b/include/linux/iommu.h
@@ -408,6 +408,7 @@ static inline void iommu_iotlb_gather_init(struct iommu_iotlb_gather *gather)
 #define IOMMU_GROUP_NOTIFY_UNBOUND_DRIVER	6 /* Post Driver unbind */
 
 extern int bus_set_iommu(struct bus_type *bus, const struct iommu_ops *ops);
+extern int bus_unset_iommu(struct bus_type *bus, const struct iommu_ops *ops);
 extern bool iommu_present(struct bus_type *bus);
 extern bool iommu_capable(struct bus_type *bus, enum iommu_cap cap);
 extern struct iommu_domain *iommu_domain_alloc(struct bus_type *bus);
-- 
2.23.0


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