block/keyslot-manager: introduce devm_blk_ksm_init()

Add a resource-managed variant of blk_ksm_init() so that drivers don't
have to worry about calling blk_ksm_destroy().

Note that the implementation uses a custom devres action to call
blk_ksm_destroy() rather than switching the two allocations to be
directly devres-managed, e.g. with devm_kmalloc().  This is because we
need to keep zeroing the memory containing the keyslots when it is
freed, and also because we want to continue using kvmalloc() (and there
is no devm_kvmalloc()).

Signed-off-by: Eric Biggers <ebiggers@google.com>
Reviewed-by: Satya Tangirala <satyat@google.com>
Acked-by: Jens Axboe <axboe@kernel.dk>
Link: https://lore.kernel.org/r/20210121082155.111333-2-ebiggers@kernel.org
Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org>

Documentation/block/inline-encryption.rst

@@ -182,8 +182,9 @@ API presented to device drivers
 
 A :c:type:``struct blk_keyslot_manager`` should be set up by device drivers in
 the ``request_queue`` of the device. The device driver needs to call
-``blk_ksm_init`` on the ``blk_keyslot_manager``, which specifying the number of
-keyslots supported by the hardware.
+``blk_ksm_init`` (or its resource-managed variant ``devm_blk_ksm_init``) on the
+``blk_keyslot_manager``, while specifying the number of keyslots supported by
+the hardware.
 
 The device driver also needs to tell the KSM how to actually manipulate the
 IE hardware in the device to do things like programming the crypto key into
@@ -202,10 +203,9 @@ needs each and every of its keyslots to be reprogrammed with the key it
 "should have" at the point in time when the function is called. This is useful
 e.g. if a device loses all its keys on runtime power down/up.
 
-``blk_ksm_destroy`` should be called to free up all resources used by a keyslot
-manager upon ``blk_ksm_init``, once the ``blk_keyslot_manager`` is no longer
-needed.
-
+If the driver used ``blk_ksm_init`` instead of ``devm_blk_ksm_init``, then
+``blk_ksm_destroy`` should be called to free up all resources used by a
+``blk_keyslot_manager`` once it is no longer needed.
 
 Layered Devices
 ===============

block/keyslot-manager.c

@@ -29,6 +29,7 @@
 #define pr_fmt(fmt) "blk-crypto: " fmt
 
 #include <linux/keyslot-manager.h>
+#include <linux/device.h>
 #include <linux/atomic.h>
 #include <linux/mutex.h>
 #include <linux/pm_runtime.h>
@@ -127,6 +128,34 @@ err_destroy_ksm:
 }
 EXPORT_SYMBOL_GPL(blk_ksm_init);
 
+static void blk_ksm_destroy_callback(void *ksm)
+{
+	blk_ksm_destroy(ksm);
+}
+
+/**
+ * devm_blk_ksm_init() - Resource-managed blk_ksm_init()
+ * @dev: The device which owns the blk_keyslot_manager.
+ * @ksm: The blk_keyslot_manager to initialize.
+ * @num_slots: The number of key slots to manage.
+ *
+ * Like blk_ksm_init(), but causes blk_ksm_destroy() to be called automatically
+ * on driver detach.
+ *
+ * Return: 0 on success, or else a negative error code.
+ */
+int devm_blk_ksm_init(struct device *dev, struct blk_keyslot_manager *ksm,
+		      unsigned int num_slots)
+{
+	int err = blk_ksm_init(ksm, num_slots);
+
+	if (err)
+		return err;
+
+	return devm_add_action_or_reset(dev, blk_ksm_destroy_callback, ksm);
+}
+EXPORT_SYMBOL_GPL(devm_blk_ksm_init);
+
 static inline struct hlist_head *
 blk_ksm_hash_bucket_for_key(struct blk_keyslot_manager *ksm,
 			    const struct blk_crypto_key *key)

include/linux/keyslot-manager.h

@@ -85,6 +85,9 @@ struct blk_keyslot_manager {
 
 int blk_ksm_init(struct blk_keyslot_manager *ksm, unsigned int num_slots);
 
+int devm_blk_ksm_init(struct device *dev, struct blk_keyslot_manager *ksm,
+		      unsigned int num_slots);
+
 blk_status_t blk_ksm_get_slot_for_key(struct blk_keyslot_manager *ksm,
 				      const struct blk_crypto_key *key,
 				      struct blk_ksm_keyslot **slot_ptr);