crypto: adiantum - add fast path for single-page messages

When the source scatterlist is a single page, optimize the first hash
step of adiantum to use crypto_shash_digest() instead of
init/update/final, and use the same local kmap for both hashing the bulk
part and loading the narrow part of the source data.

Likewise, when the destination scatterlist is a single page, optimize
the second hash step of adiantum to use crypto_shash_digest() instead of
init/update/final, and use the same local kmap for both hashing the bulk
part and storing the narrow part of the destination data.

In some cases these optimizations improve performance significantly.

Note: ideally, for optimal performance each architecture should
implement the full "adiantum(xchacha12,aes)" algorithm and fully
optimize the contiguous buffer case to use no indirect calls.  That's
not something I've gotten around to doing, though.  This commit just
makes a relatively small change that provides some benefit with the
existing template-based approach.
Signed-off-by: Eric Biggers <ebiggers@google.com>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>

crypto/adiantum.c

@@ -245,10 +245,9 @@ static void adiantum_hash_header(struct skcipher_request *req)
 
 /* Hash the left-hand part (the "bulk") of the message using NHPoly1305 */
 static int adiantum_hash_message(struct skcipher_request *req,
-				 struct scatterlist *sgl, le128 *digest)
+				 struct scatterlist *sgl, unsigned int nents,
+				 le128 *digest)
 {
-	struct crypto_skcipher *tfm = crypto_skcipher_reqtfm(req);
-	const struct adiantum_tfm_ctx *tctx = crypto_skcipher_ctx(tfm);
 	struct adiantum_request_ctx *rctx = skcipher_request_ctx(req);
 	const unsigned int bulk_len = req->cryptlen - BLOCKCIPHER_BLOCK_SIZE;
 	struct shash_desc *hash_desc = &rctx->u.hash_desc;
@@ -256,14 +255,11 @@ static int adiantum_hash_message(struct skcipher_request *req,
 	unsigned int i, n;
 	int err;
 
-	hash_desc->tfm = tctx->hash;
-
 	err = crypto_shash_init(hash_desc);
 	if (err)
 		return err;
 
-	sg_miter_start(&miter, sgl, sg_nents(sgl),
-		       SG_MITER_FROM_SG | SG_MITER_ATOMIC);
+	sg_miter_start(&miter, sgl, nents, SG_MITER_FROM_SG | SG_MITER_ATOMIC);
 	for (i = 0; i < bulk_len; i += n) {
 		sg_miter_next(&miter);
 		n = min_t(unsigned int, miter.length, bulk_len - i);
@@ -285,6 +281,8 @@ static int adiantum_finish(struct skcipher_request *req)
 	const struct adiantum_tfm_ctx *tctx = crypto_skcipher_ctx(tfm);
 	struct adiantum_request_ctx *rctx = skcipher_request_ctx(req);
 	const unsigned int bulk_len = req->cryptlen - BLOCKCIPHER_BLOCK_SIZE;
+	struct scatterlist *dst = req->dst;
+	const unsigned int dst_nents = sg_nents(dst);
 	le128 digest;
 	int err;
 
@@ -298,13 +296,30 @@ static int adiantum_finish(struct skcipher_request *req)
 	 *	enc: C_R = C_M - H_{K_H}(T, C_L)
 	 *	dec: P_R = P_M - H_{K_H}(T, P_L)
 	 */
-	err = adiantum_hash_message(req, req->dst, &digest);
+	rctx->u.hash_desc.tfm = tctx->hash;
+	le128_sub(&rctx->rbuf.bignum, &rctx->rbuf.bignum, &rctx->header_hash);
+	if (dst_nents == 1 && dst->offset + req->cryptlen <= PAGE_SIZE) {
+		/* Fast path for single-page destination */
+		void *virt = kmap_local_page(sg_page(dst)) + dst->offset;
+
+		err = crypto_shash_digest(&rctx->u.hash_desc, virt, bulk_len,
+					  (u8 *)&digest);
+		if (err) {
+			kunmap_local(virt);
+			return err;
+		}
+		le128_sub(&rctx->rbuf.bignum, &rctx->rbuf.bignum, &digest);
+		memcpy(virt + bulk_len, &rctx->rbuf.bignum, sizeof(le128));
+		kunmap_local(virt);
+	} else {
+		/* Slow path that works for any destination scatterlist */
+		err = adiantum_hash_message(req, dst, dst_nents, &digest);
 		if (err)
 			return err;
-	le128_add(&digest, &digest, &rctx->header_hash);
 		le128_sub(&rctx->rbuf.bignum, &rctx->rbuf.bignum, &digest);
-	scatterwalk_map_and_copy(&rctx->rbuf.bignum, req->dst,
-				 bulk_len, BLOCKCIPHER_BLOCK_SIZE, 1);
+		scatterwalk_map_and_copy(&rctx->rbuf.bignum, dst,
+					 bulk_len, sizeof(le128), 1);
+	}
 	return 0;
 }
 
@@ -324,6 +339,8 @@ static int adiantum_crypt(struct skcipher_request *req, bool enc)
 	const struct adiantum_tfm_ctx *tctx = crypto_skcipher_ctx(tfm);
 	struct adiantum_request_ctx *rctx = skcipher_request_ctx(req);
 	const unsigned int bulk_len = req->cryptlen - BLOCKCIPHER_BLOCK_SIZE;
+	struct scatterlist *src = req->src;
+	const unsigned int src_nents = sg_nents(src);
 	unsigned int stream_len;
 	le128 digest;
 	int err;
@@ -339,12 +356,24 @@ static int adiantum_crypt(struct skcipher_request *req, bool enc)
 	 *	dec: C_M = C_R + H_{K_H}(T, C_L)
 	 */
 	adiantum_hash_header(req);
-	err = adiantum_hash_message(req, req->src, &digest);
+	rctx->u.hash_desc.tfm = tctx->hash;
+	if (src_nents == 1 && src->offset + req->cryptlen <= PAGE_SIZE) {
+		/* Fast path for single-page source */
+		void *virt = kmap_local_page(sg_page(src)) + src->offset;
+
+		err = crypto_shash_digest(&rctx->u.hash_desc, virt, bulk_len,
+					  (u8 *)&digest);
+		memcpy(&rctx->rbuf.bignum, virt + bulk_len, sizeof(le128));
+		kunmap_local(virt);
+	} else {
+		/* Slow path that works for any source scatterlist */
+		err = adiantum_hash_message(req, src, src_nents, &digest);
+		scatterwalk_map_and_copy(&rctx->rbuf.bignum, src,
+					 bulk_len, sizeof(le128), 0);
+	}
 	if (err)
 		return err;
-	le128_add(&digest, &digest, &rctx->header_hash);
-	scatterwalk_map_and_copy(&rctx->rbuf.bignum, req->src,
-				 bulk_len, BLOCKCIPHER_BLOCK_SIZE, 0);
+	le128_add(&rctx->rbuf.bignum, &rctx->rbuf.bignum, &rctx->header_hash);
 	le128_add(&rctx->rbuf.bignum, &rctx->rbuf.bignum, &digest);
 
 	/* If encrypting, encrypt P_M with the block cipher to get C_M */