iommu/ioasid: Add custom allocators

IOASID allocation may rely on platform specific methods. One use case is
that when running in the guest, in order to obtain system wide global
IOASIDs, emulated allocation interface is needed to communicate with the
host. Here we call these platform specific allocators custom allocators.

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@linaro.com>
Signed-off-by: Jacob Pan <jacob.jun.pan@linux.intel.com>
Link: https://lkml.org/lkml/2019/4/26/462Reviewed-by: Jean-Philippe Brucker <jean-philippe@linaro.org>
Reviewed-by: Eric Auger <eric.auger@redhat.com>
Signed-off-by: Joerg Roedel <jroedel@suse.de>

include/linux/ioasid.h

@@ -7,11 +7,28 @@
 
 #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)
@@ -20,6 +37,8 @@ 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 */
@@ -39,6 +58,15 @@ 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 -ENOTSUPP;
+}
+
+static inline void ioasid_unregister_allocator(struct ioasid_allocator_ops *allocator)
+{
+}
+
 static inline int ioasid_set_data(ioasid_t ioasid, void *data)
 {
 	return -ENOTSUPP;