[PATCH v3 04/16] ioasid: Add custom IOASID allocator

[Jacob Pan]

Sometimes, IOASID allocation must be handled by platform specific
code. The use cases are guest vIOMMU and pvIOMMU where IOASIDs need
to be allocated by the host via enlightened or paravirt interfaces.

This patch adds an extension to the IOASID allocator APIs such that
platform drivers can register a custom allocator, possibly at boot
time, to take over the allocation. Xarray is still used for tracking
and searching purposes internal to the IOASID code. Private data of
an IOASID can also be set after the allocation.

There can be multiple custom allocators registered but only one is
used at a time. In case of hot removal of devices that provides the
allocator, all IOASIDs must be freed prior to unregistering the
allocator. Default XArray based allocator cannot be mixed with
custom allocators, i.e. custom allocators will not be used if there
are outstanding IOASIDs allocated by the default XA allocator.

Signed-off-by: Jacob Pan <jacob.jun.pan@xxxxxxxxxxxxxxx>
---
 drivers/iommu/ioasid.c | 125 +++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 125 insertions(+)

diff --git a/drivers/iommu/ioasid.c b/drivers/iommu/ioasid.c
index 99f5e0a..ed2915a 100644
--- a/drivers/iommu/ioasid.c
+++ b/drivers/iommu/ioasid.c
@@ -17,6 +17,100 @@ struct ioasid_data {
 };
 
 static DEFINE_XARRAY_ALLOC(ioasid_xa);
+static DEFINE_MUTEX(ioasid_allocator_lock);
+static struct ioasid_allocator *active_custom_allocator;
+
+static LIST_HEAD(custom_allocators);
+/*
+ * A flag to track if ioasid default allocator is in use, this will
+ * prevent custom allocator from being used. The reason is that custom allocator
+ * must have unadulterated space to track private data with xarray, there cannot
+ * be a mix been default and custom allocated IOASIDs.
+ */
+static int default_allocator_active;
+
+/**
+ * ioasid_register_allocator - register a custom allocator
+ * @allocator: the custom allocator to be registered
+ *
+ * Custom allocators take precedence over the default xarray based allocator.
+ * Private data associated with the ASID are managed by ASID common code
+ * similar to data stored in xa.
+ *
+ * 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.
+ */
+int ioasid_register_allocator(struct ioasid_allocator *allocator)
+{
+	struct ioasid_allocator *pallocator;
+	int ret = 0;
+
+	if (!allocator)
+		return -EINVAL;
+
+	mutex_lock(&ioasid_allocator_lock);
+	/*
+	 * No particular preference since all custom allocators end up calling
+	 * the host to allocate IOASIDs. 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(&custom_allocators))
+		active_custom_allocator = allocator;
+	else {
+		/* Check if the allocator is already registered */
+		list_for_each_entry(pallocator, &custom_allocators, list) {
+			if (pallocator == allocator) {
+				pr_err("IOASID allocator already registered\n");
+				ret = -EEXIST;
+				goto out_unlock;
+			}
+		}
+	}
+	list_add_tail(&allocator->list, &custom_allocators);
+
+out_unlock:
+	mutex_unlock(&ioasid_allocator_lock);
+	return ret;
+}
+EXPORT_SYMBOL_GPL(ioasid_register_allocator);
+
+/**
+ * ioasid_unregister_allocator - Remove a custom IOASID allocator
+ * @allocator: the custom allocator to be removed
+ *
+ * Remove an allocator from the list, activate the next allocator in
+ * the order it was registered.
+ */
+void ioasid_unregister_allocator(struct ioasid_allocator *allocator)
+{
+	if (!allocator)
+		return;
+
+	if (list_empty(&custom_allocators)) {
+		pr_warn("No custom IOASID allocators active!\n");
+		return;
+	}
+
+	mutex_lock(&ioasid_allocator_lock);
+	list_del(&allocator->list);
+	if (list_empty(&custom_allocators)) {
+		pr_info("No custom IOASID allocators\n");
+		/*
+		 * All IOASIDs should have been freed before the last custom
+		 * allocator is unregistered. Unless default allocator is in
+		 * use.
+		 */
+		BUG_ON(!xa_empty(&ioasid_xa) && !default_allocator_active);
+		active_custom_allocator = NULL;
+	} else if (allocator == active_custom_allocator) {
+		active_custom_allocator = list_entry(&custom_allocators, struct ioasid_allocator, list);
+		pr_info("IOASID allocator changed");
+	}
+	mutex_unlock(&ioasid_allocator_lock);
+}
+EXPORT_SYMBOL_GPL(ioasid_unregister_allocator);
 
 /**
  * ioasid_set_data - Set private data for an allocated ioasid
@@ -68,6 +162,29 @@ ioasid_t ioasid_alloc(struct ioasid_set *set, ioasid_t min, ioasid_t max,
 	data->set = set;
 	data->private = private;
 
+	mutex_lock(&ioasid_allocator_lock);
+	/*
+	 * Use custom allocator if available, otherwise use default.
+	 * However, if there are active IOASIDs already been allocated by default
+	 * allocator, custom allocator cannot be used.
+	 */
+	if (!default_allocator_active && active_custom_allocator) {
+		id = active_custom_allocator->alloc(min, max, active_custom_allocator->pdata);
+		if (id == INVALID_IOASID) {
+			pr_err("Failed ASID allocation by custom allocator\n");
+			mutex_unlock(&ioasid_allocator_lock);
+			goto exit_free;
+		}
+		/*
+		 * Use XA to manage private data also sanitiy check custom
+		 * allocator for duplicates.
+		 */
+		min = id;
+		max = id + 1;
+	} else
+		default_allocator_active = 1;
+	mutex_unlock(&ioasid_allocator_lock);
+
 	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);
 		goto exit_free;
@@ -91,9 +208,17 @@ void ioasid_free(ioasid_t ioasid)
 {
 	struct ioasid_data *ioasid_data;
 
+	mutex_lock(&ioasid_allocator_lock);
+	if (active_custom_allocator)
+		active_custom_allocator->free(ioasid, active_custom_allocator->pdata);
+	mutex_unlock(&ioasid_allocator_lock);
+
 	ioasid_data = xa_erase(&ioasid_xa, ioasid);
 
 	kfree_rcu(ioasid_data, rcu);
+
+	if (xa_empty(&ioasid_xa))
+		default_allocator_active = 0;
 }
 EXPORT_SYMBOL_GPL(ioasid_free);
 
-- 
2.7.4