[PATCH v6 02/25] iommu/ioasid: Add ioasid references

[Jean-Philippe Brucker <jean-philippe@xxxxxxxxxx>]

Let IOASID users take references to existing ioasids with ioasid_get().
ioasid_free() drops a reference and only frees the ioasid when its
reference number is zero. It returns whether the ioasid was freed.

Signed-off-by: Jean-Philippe Brucker <jean-philippe@xxxxxxxxxx>
---
 include/linux/ioasid.h | 10 ++++++++--
 drivers/iommu/ioasid.c | 30 +++++++++++++++++++++++++++++-
 2 files changed, 37 insertions(+), 3 deletions(-)

diff --git a/include/linux/ioasid.h b/include/linux/ioasid.h
index 6f000d7a0ddcd..609ba6f15b9e3 100644
--- a/include/linux/ioasid.h
+++ b/include/linux/ioasid.h
@@ -34,7 +34,8 @@ struct ioasid_allocator_ops {
 #if IS_ENABLED(CONFIG_IOASID)
 ioasid_t ioasid_alloc(struct ioasid_set *set, ioasid_t min, ioasid_t max,
 		      void *private);
-void ioasid_free(ioasid_t ioasid);
+void ioasid_get(ioasid_t ioasid);
+bool ioasid_free(ioasid_t ioasid);
 void *ioasid_find(struct ioasid_set *set, ioasid_t ioasid,
 		  bool (*getter)(void *));
 int ioasid_register_allocator(struct ioasid_allocator_ops *allocator);
@@ -48,10 +49,15 @@ static inline ioasid_t ioasid_alloc(struct ioasid_set *set, ioasid_t min,
 	return INVALID_IOASID;
 }
 
-static inline void ioasid_free(ioasid_t ioasid)
+static inline void ioasid_get(ioasid_t ioasid)
 {
 }
 
+static inline bool ioasid_free(ioasid_t ioasid)
+{
+	return false;
+}
+
 static inline void *ioasid_find(struct ioasid_set *set, ioasid_t ioasid,
 				bool (*getter)(void *))
 {
diff --git a/drivers/iommu/ioasid.c b/drivers/iommu/ioasid.c
index 0f8dd377aada3..46511ac53e0c8 100644
--- a/drivers/iommu/ioasid.c
+++ b/drivers/iommu/ioasid.c
@@ -15,6 +15,7 @@ struct ioasid_data {
 	struct ioasid_set *set;
 	void *private;
 	struct rcu_head rcu;
+	refcount_t refs;
 };
 
 /*
@@ -314,6 +315,7 @@ ioasid_t ioasid_alloc(struct ioasid_set *set, ioasid_t min, ioasid_t max,
 
 	data->set = set;
 	data->private = private;
+	refcount_set(&data->refs, 1);
 
 	/*
 	 * Custom allocator needs allocator data to perform platform specific
@@ -345,12 +347,33 @@ ioasid_t ioasid_alloc(struct ioasid_set *set, ioasid_t min, ioasid_t max,
 }
 EXPORT_SYMBOL_GPL(ioasid_alloc);
 
+/**
+ * ioasid_get - obtain a reference to the IOASID
+ */
+void ioasid_get(ioasid_t ioasid)
+{
+	struct ioasid_data *ioasid_data;
+
+	spin_lock(&ioasid_allocator_lock);
+	ioasid_data = xa_load(&active_allocator->xa, ioasid);
+	if (ioasid_data)
+		refcount_inc(&ioasid_data->refs);
+	spin_unlock(&ioasid_allocator_lock);
+}
+EXPORT_SYMBOL_GPL(ioasid_get);
+
 /**
  * ioasid_free - Free an IOASID
  * @ioasid: the ID to remove
+ *
+ * Put a reference to the IOASID, free it when the number of references drops to
+ * zero.
+ *
+ * Return: %true if the IOASID was freed, %false otherwise.
  */
-void ioasid_free(ioasid_t ioasid)
+bool ioasid_free(ioasid_t ioasid)
 {
+	bool free = false;
 	struct ioasid_data *ioasid_data;
 
 	spin_lock(&ioasid_allocator_lock);
@@ -360,6 +383,10 @@ void ioasid_free(ioasid_t ioasid)
 		goto exit_unlock;
 	}
 
+	free = refcount_dec_and_test(&ioasid_data->refs);
+	if (!free)
+		goto exit_unlock;
+
 	active_allocator->ops->free(ioasid, active_allocator->ops->pdata);
 	/* Custom allocator needs additional steps to free the xa element */
 	if (active_allocator->flags & IOASID_ALLOCATOR_CUSTOM) {
@@ -369,6 +396,7 @@ void ioasid_free(ioasid_t ioasid)
 
 exit_unlock:
 	spin_unlock(&ioasid_allocator_lock);
+	return free;
 }
 EXPORT_SYMBOL_GPL(ioasid_free);
 
-- 
2.26.2