[PATCH v5 08/19] iommu/ioasid: Add custom allocators

[Jacob Pan <jacob.jun.pan@linux.intel.com>]

Custom IOASID allocators can be registered at runtime and take precedence
over the default XArray allocator. They have these attributes:

- provides platform specific alloc()/free() functions with private data.
- allocation results lookup are not provided by the allocator, lookup
  request must be done by the IOASID framework by its own XArray.
- allocators can be unregistered at runtime, either fallback to the next
  custom allocator or to the default allocator.
- custom allocators can share the same set of alloc()/free() helpers, in
  this case they also share the same IOASID space, thus the same XArray.
- switching between allocators requires all outstanding IOASIDs to be
  freed unless the two allocators share the same alloc()/free() helpers.

Signed-off-by: Jean-Philippe Brucker <jean-philippe.brucker@arm.com>
Signed-off-by: Jacob Pan <jacob.jun.pan@linux.intel.com>
Link: https://lkml.org/lkml/2019/4/26/462
---
 drivers/iommu/ioasid.c | 302 +++++++++++++++++++++++++++++++++++++++++++++++--
 include/linux/ioasid.h |  28 +++++
 2 files changed, 320 insertions(+), 10 deletions(-)

diff --git a/drivers/iommu/ioasid.c b/drivers/iommu/ioasid.c
index 6fbea76..b2d9ea5 100644
--- a/drivers/iommu/ioasid.c
+++ b/drivers/iommu/ioasid.c
@@ -17,7 +17,254 @@ struct ioasid_data {
 	struct rcu_head rcu;
 };
 
-static DEFINE_XARRAY_ALLOC(ioasid_xa);
+/*
+ * struct ioasid_allocator_data - Internal data structure to hold information
+ * about an allocator. There are two types of allocators:
+ *
+ * - Default allocator always has its own XArray to track the IOASIDs allocated.
+ * - Custom allocators may share allocation helpers with different private data.
+ *   Custom allocators share the same helper functions also share the same
+ *   XArray.
+ * Rules:
+ * 1. Default allocator is always available, not dynamically registered. This is
+ *    to prevent race conditions with early boot code that want to register
+ *    custom allocators or allocate IOASIDs.
+ * 2. Custom allocators take precedence over the default allocator.
+ * 3. When all custom allocators sharing the same helper functions are
+ *    unregistered (e.g. due to hotplug), all outstanding IOASIDs must be
+ *    freed.
+ * 4. When switching between custom allocators sharing the same helper
+ *    functions, outstanding IOASIDs are preserved.
+ * 5. When switching between custom allocator and default allocator, all IOASIDs
+ *    must be freed to ensure unadulterated space for the new allocator.
+ *
+ * @ops:	allocator helper functions and its data
+ * @list:	registered custom allocators
+ * @slist:	allocators share the same ops but different data
+ * @flags:	attributes of the allocator
+ * @xa		xarray holds the IOASID space
+ * @users	number of allocators sharing the same ops and XArray
+ */
+struct ioasid_allocator_data {
+	struct ioasid_allocator_ops *ops;
+	struct list_head list;
+	struct list_head slist;
+#define IOASID_ALLOCATOR_CUSTOM BIT(0) /* Needs framework to track results */
+	unsigned long flags;
+	struct xarray xa;
+	refcount_t users;
+};
+
+static DEFINE_MUTEX(ioasid_allocator_lock);
+static LIST_HEAD(allocators_list);
+
+static ioasid_t default_alloc(ioasid_t min, ioasid_t max, void *opaque);
+static void default_free(ioasid_t ioasid, void *opaque);
+
+static struct ioasid_allocator_ops default_ops = {
+	.alloc = default_alloc,
+	.free = default_free,
+};
+
+static struct ioasid_allocator_data default_allocator = {
+	.ops = &default_ops,
+	.flags = 0,
+	.xa = XARRAY_INIT(ioasid_xa, XA_FLAGS_ALLOC),
+};
+
+static struct ioasid_allocator_data *active_allocator = &default_allocator;
+
+static ioasid_t default_alloc(ioasid_t min, ioasid_t max, void *opaque)
+{
+	ioasid_t id;
+
+	if (xa_alloc(&default_allocator.xa, &id, opaque, XA_LIMIT(min, max), GFP_KERNEL)) {
+		pr_err("Failed to alloc ioasid from %d to %d\n", min, max);
+		return INVALID_IOASID;
+	}
+
+	return id;
+}
+
+static void default_free(ioasid_t ioasid, void *opaque)
+{
+	struct ioasid_data *ioasid_data;
+
+	ioasid_data = xa_erase(&default_allocator.xa, ioasid);
+	kfree_rcu(ioasid_data, rcu);
+}
+
+/* Allocate and initialize a new custom allocator with its helper functions */
+static struct ioasid_allocator_data *ioasid_alloc_allocator(struct ioasid_allocator_ops *ops)
+{
+	struct ioasid_allocator_data *ia_data;
+
+	ia_data = kzalloc(sizeof(*ia_data), GFP_KERNEL);
+	if (!ia_data)
+		return NULL;
+
+	xa_init_flags(&ia_data->xa, XA_FLAGS_ALLOC);
+	INIT_LIST_HEAD(&ia_data->slist);
+	ia_data->flags |= IOASID_ALLOCATOR_CUSTOM;
+	ia_data->ops = ops;
+
+	/* For tracking custom allocators that share the same ops */
+	list_add_tail(&ops->list, &ia_data->slist);
+	refcount_set(&ia_data->users, 1);
+
+	return ia_data;
+}
+
+static bool use_same_ops(struct ioasid_allocator_ops *a, struct ioasid_allocator_ops *b)
+{
+	return (a->free == b->free) && (a->alloc == b->alloc);
+}
+
+/**
+ * ioasid_register_allocator - register a custom allocator
+ * @ops: the custom allocator ops to be registered
+ *
+ * Custom allocators take precedence over the default xarray based allocator.
+ * Private data associated with the IOASID allocated by the custom allocators
+ * are managed by IOASID framework similar to data stored in xa by default
+ * allocator.
+ *
+ * There can be multiple allocators registered but only one is active. In case
+ * of runtime removal of a custom allocator, the next one is activated based
+ * on the registration ordering.
+ *
+ * Multiple allocators can share the same alloc() function, in this case the
+ * IOASID space is shared.
+ */
+int ioasid_register_allocator(struct ioasid_allocator_ops *ops)
+{
+	struct ioasid_allocator_data *ia_data;
+	struct ioasid_allocator_data *pallocator;
+	int ret = 0;
+
+	mutex_lock(&ioasid_allocator_lock);
+
+	ia_data = ioasid_alloc_allocator(ops);
+	if (!ia_data) {
+		ret = -ENOMEM;
+		goto out_unlock;
+	}
+
+	/*
+	 * No particular preference, we activate the first one and keep
+	 * the later registered allocators in a list in case the first one gets
+	 * removed due to hotplug.
+	 */
+	if (list_empty(&allocators_list)) {
+		WARN_ON(active_allocator != &default_allocator);
+		/* Use this new allocator if default is not active */
+		if (xa_empty(&active_allocator->xa)) {
+			active_allocator = ia_data;
+			list_add_tail(&ia_data->list, &allocators_list);
+			goto out_unlock;
+		}
+		pr_warn("Default allocator active with outstanding IOASID\n");
+		ret = -EAGAIN;
+		goto out_free;
+	}
+
+	/* Check if the allocator is already registered */
+	list_for_each_entry(pallocator, &allocators_list, list) {
+		if (pallocator->ops == ops) {
+			pr_err("IOASID allocator already registered\n");
+			ret = -EEXIST;
+			goto out_free;
+		} else if (use_same_ops(pallocator->ops, ops)) {
+			/*
+			 * If the new allocator shares the same ops,
+			 * then they will share the same IOASID space.
+			 * We should put them under the same xarray.
+			 */
+			list_add_tail(&ops->list, &pallocator->slist);
+			refcount_inc(&pallocator->users);
+			pr_info("New IOASID allocator ops shared %u times\n",
+				refcount_read(&pallocator->users));
+			goto out_free;
+		}
+	}
+	list_add_tail(&ia_data->list, &allocators_list);
+
+	mutex_unlock(&ioasid_allocator_lock);
+	return 0;
+out_free:
+	kfree(ia_data);
+out_unlock:
+	mutex_unlock(&ioasid_allocator_lock);
+	return ret;
+}
+EXPORT_SYMBOL_GPL(ioasid_register_allocator);
+
+static inline bool has_shared_ops(struct ioasid_allocator_data *allocator)
+{
+	return refcount_read(&allocator->users) > 1;
+}
+
+/**
+ * ioasid_unregister_allocator - Remove a custom IOASID allocator ops
+ * @ops: the custom allocator to be removed
+ *
+ * Remove an allocator from the list, activate the next allocator in
+ * the order it was registered. Or revert to default allocator if all
+ * custom allocators are unregistered without outstanding IOASIDs.
+ */
+void ioasid_unregister_allocator(struct ioasid_allocator_ops *ops)
+{
+	struct ioasid_allocator_data *pallocator;
+	struct ioasid_allocator_ops *sops;
+
+	mutex_lock(&ioasid_allocator_lock);
+	if (list_empty(&allocators_list)) {
+		pr_warn("No custom IOASID allocators active!\n");
+		goto exit_unlock;
+	}
+
+	list_for_each_entry(pallocator, &allocators_list, list) {
+		if (!use_same_ops(pallocator->ops, ops))
+			continue;
+
+		if (refcount_read(&pallocator->users) == 1) {
+			/* No shared helper functions */
+			list_del(&pallocator->list);
+			/*
+			 * All IOASIDs should have been freed before
+			 * the last allocator that shares the same ops
+			 * is unregistered.
+			 */
+			WARN_ON(!xa_empty(&pallocator->xa));
+			kfree(pallocator);
+			if (list_empty(&allocators_list)) {
+				pr_info("No custom IOASID allocators, switch to default.\n");
+				active_allocator = &default_allocator;
+			} else if (pallocator == active_allocator) {
+				active_allocator = list_first_entry(&allocators_list, struct ioasid_allocator_data, list);
+				pr_info("IOASID allocator changed");
+			}
+			break;
+		}
+		/*
+		 * Find the matching shared ops to delete,
+		 * but keep outstanding IOASIDs
+		 */
+		list_for_each_entry(sops, &pallocator->slist, list) {
+			if (sops == ops) {
+				list_del(&ops->list);
+				if (refcount_dec_and_test(&pallocator->users))
+					pr_err("no shared ops\n");
+				break;
+			}
+		}
+		break;
+	}
+
+exit_unlock:
+	mutex_unlock(&ioasid_allocator_lock);
+}
+EXPORT_SYMBOL_GPL(ioasid_unregister_allocator);
 
 /**
  * ioasid_set_data - Set private data for an allocated ioasid
@@ -32,13 +279,13 @@ int ioasid_set_data(ioasid_t ioasid, void *data)
 	struct ioasid_data *ioasid_data;
 	int ret = 0;
 
-	xa_lock(&ioasid_xa);
-	ioasid_data = xa_load(&ioasid_xa, ioasid);
+	mutex_lock(&ioasid_allocator_lock);
+	ioasid_data = xa_load(&active_allocator->xa, ioasid);
 	if (ioasid_data)
 		rcu_assign_pointer(ioasid_data->private, data);
 	else
 		ret = -ENOENT;
-	xa_unlock(&ioasid_xa);
+	mutex_unlock(&ioasid_allocator_lock);
 
 	/*
 	 * Wait for readers to stop accessing the old private data, so the
@@ -66,8 +313,9 @@ EXPORT_SYMBOL_GPL(ioasid_set_data);
 ioasid_t ioasid_alloc(struct ioasid_set *set, ioasid_t min, ioasid_t max,
 		      void *private)
 {
-	ioasid_t id;
 	struct ioasid_data *data;
+	void *adata;
+	ioasid_t id;
 
 	data = kzalloc(sizeof(*data), GFP_KERNEL);
 	if (!data)
@@ -76,14 +324,34 @@ ioasid_t ioasid_alloc(struct ioasid_set *set, ioasid_t min, ioasid_t max,
 	data->set = set;
 	data->private = private;
 
-	if (xa_alloc(&ioasid_xa, &id, data, XA_LIMIT(min, max), GFP_KERNEL)) {
-		pr_err("Failed to alloc ioasid from %d to %d\n", min, max);
+	/*
+	 * Custom allocator needs allocator data to perform platform specific
+	 * operations.
+	 */
+	adata = active_allocator->flags & IOASID_ALLOCATOR_CUSTOM ? active_allocator->ops->pdata : data;
+	mutex_lock(&ioasid_allocator_lock);
+	id = active_allocator->ops->alloc(min, max, adata);
+	if (id == INVALID_IOASID) {
+		pr_err("Failed ASID allocation %lu\n", active_allocator->flags);
 		goto exit_free;
 	}
+
+	if (active_allocator->flags & IOASID_ALLOCATOR_CUSTOM) {
+		/* Custom allocator needs framework to store and track allocation results */
+		min = max = id;
+
+		if (xa_alloc(&active_allocator->xa, &id, data, XA_LIMIT(min, max), GFP_KERNEL)) {
+			pr_err("Failed to alloc ioasid from %d to %d\n", min, max);
+			active_allocator->ops->free(id, NULL);
+			goto exit_free;
+		}
+	}
 	data->id = id;
 
+	mutex_unlock(&ioasid_allocator_lock);
 	return id;
 exit_free:
+	mutex_unlock(&ioasid_allocator_lock);
 	kfree(data);
 	return INVALID_IOASID;
 }
@@ -97,9 +365,23 @@ void ioasid_free(ioasid_t ioasid)
 {
 	struct ioasid_data *ioasid_data;
 
-	ioasid_data = xa_erase(&ioasid_xa, ioasid);
+	mutex_lock(&ioasid_allocator_lock);
 
-	kfree_rcu(ioasid_data, rcu);
+	ioasid_data = xa_load(&active_allocator->xa, ioasid);
+	if (!ioasid_data) {
+		pr_err("Trying to free unknown IOASID %u\n", ioasid);
+		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) {
+		ioasid_data = xa_erase(&active_allocator->xa, ioasid);
+		kfree_rcu(ioasid_data, rcu);
+	}
+
+exit_unlock:
+	mutex_unlock(&ioasid_allocator_lock);
 }
 EXPORT_SYMBOL_GPL(ioasid_free);
 
@@ -124,7 +406,7 @@ void *ioasid_find(struct ioasid_set *set, ioasid_t ioasid,
 	struct ioasid_data *ioasid_data;
 
 	rcu_read_lock();
-	ioasid_data = xa_load(&ioasid_xa, ioasid);
+	ioasid_data = xa_load(&active_allocator->xa, ioasid);
 	if (!ioasid_data) {
 		priv = ERR_PTR(-ENOENT);
 		goto unlock;
diff --git a/include/linux/ioasid.h b/include/linux/ioasid.h
index 0c272d9..33ef3ea 100644
--- a/include/linux/ioasid.h
+++ b/include/linux/ioasid.h
@@ -6,11 +6,28 @@
 
 #define INVALID_IOASID ((ioasid_t)-1)
 typedef unsigned int ioasid_t;
+typedef ioasid_t (*ioasid_alloc_fn_t)(ioasid_t min, ioasid_t max, void *data);
+typedef void (*ioasid_free_fn_t)(ioasid_t ioasid, void *data);
 
 struct ioasid_set {
 	int dummy;
 };
 
+/**
+ * struct ioasid_allocator_ops - IOASID allocator helper functions and data
+ *
+ * @alloc:	helper function to allocate IOASID
+ * @free:	helper function to free IOASID
+ * @list:	for tracking ops that share helper functions but not data
+ * @pdata:	data belong to the allocator, provided when calling alloc()
+ */
+struct ioasid_allocator_ops {
+	ioasid_alloc_fn_t alloc;
+	ioasid_free_fn_t free;
+	struct list_head list;
+	void *pdata;
+};
+
 #define DECLARE_IOASID_SET(name) struct ioasid_set name = { 0 }
 
 #if IS_ENABLED(CONFIG_IOASID)
@@ -19,6 +36,8 @@ ioasid_t ioasid_alloc(struct ioasid_set *set, ioasid_t min, ioasid_t max,
 void 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);
+void ioasid_unregister_allocator(struct ioasid_allocator_ops *allocator);
 int ioasid_set_data(ioasid_t ioasid, void *data);
 
 #else /* !CONFIG_IOASID */
@@ -38,6 +57,15 @@ static inline void *ioasid_find(struct ioasid_set *set, ioasid_t ioasid,
 	return NULL;
 }
 
+static inline int ioasid_register_allocator(struct ioasid_allocator_ops *allocator)
+{
+	return -ENODEV;
+}
+
+static inline void ioasid_unregister_allocator(struct ioasid_allocator_ops *allocator)
+{
+}
+
 static inline int ioasid_set_data(ioasid_t ioasid, void *data)
 {
 	return -ENODEV;
-- 
2.7.4

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