blk-crypto: handle the fallback above the block layer

Add a blk_crypto_submit_bio helper that either submits the bio when
it is not encrypted or inline encryption is provided, but otherwise
handles the encryption before going down into the low-level driver.
This reduces the risk from bio reordering and keeps memory allocation
as high up in the stack as possible.

Note that if the submitter knows that inline enctryption is known to
be supported by the underyling driver, it can still use plain
submit_bio.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Eric Biggers <ebiggers@kernel.org>
Signed-off-by: Jens Axboe <axboe@kernel.dk>

1 files changed, 22 insertions, 0 deletions

diff --git a/include/linux/blk-crypto.h b/include/linux/blk-crypto.h
index eb80df19be68..f7c3cb4a342f 100644
--- a/include/linux/blk-crypto.h
+++ b/include/linux/blk-crypto.h
@@ -181,6 +181,28 @@ static inline struct bio_crypt_ctx *bio_crypt_ctx(struct bio *bio)
 
 #endif /* CONFIG_BLK_INLINE_ENCRYPTION */
 
+bool __blk_crypto_submit_bio(struct bio *bio);
+
+/**
+ * blk_crypto_submit_bio - Submit a bio that may have a crypto context
+ * @bio: bio to submit
+ *
+ * If @bio has no crypto context, or the crypt context attached to @bio is
+ * supported by the underlying device's inline encryption hardware, just submit
+ * @bio.
+ *
+ * Otherwise, try to perform en/decryption for this bio by falling back to the
+ * kernel crypto API. For encryption this means submitting newly allocated
+ * bios for the encrypted payload while keeping back the source bio until they
+ * complete, while for reads the decryption happens in-place by a hooked in
+ * completion handler.
+ */
+static inline void blk_crypto_submit_bio(struct bio *bio)
+{
+	if (!bio_has_crypt_ctx(bio) || __blk_crypto_submit_bio(bio))
+		submit_bio(bio);
+}
+
 int __bio_crypt_clone(struct bio *dst, struct bio *src, gfp_t gfp_mask);
 /**
  * bio_crypt_clone - clone bio encryption context