[RFC PATCH 02/18] crypto: x86/poly1305 - implement .update_from_sg method

[Ard Biesheuvel <ard.biesheuvel@linaro.org>]

In order to reduce the number of invocations of the RFC7539 template
into the Poly1305 driver, implement the new internal .update_from_sg
method that allows the driver to amortize the cost of FPU preserve/
restore sequences over a larger chunk of input.

Signed-off-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>
---
 arch/x86/crypto/poly1305_glue.c | 54 ++++++++++++++++----
 1 file changed, 43 insertions(+), 11 deletions(-)

diff --git a/arch/x86/crypto/poly1305_glue.c b/arch/x86/crypto/poly1305_glue.c
index 4a1c05dce950..f2afaa8e23c2 100644
--- a/arch/x86/crypto/poly1305_glue.c
+++ b/arch/x86/crypto/poly1305_glue.c
@@ -115,18 +115,11 @@ static unsigned int poly1305_simd_blocks(struct poly1305_desc_ctx *dctx,
 	return srclen;
 }
 
-static int poly1305_simd_update(struct shash_desc *desc,
-				const u8 *src, unsigned int srclen)
+static void poly1305_simd_do_update(struct shash_desc *desc,
+				    const u8 *src, unsigned int srclen)
 {
-	struct poly1305_desc_ctx *dctx = shash_desc_ctx(desc);
 	unsigned int bytes;
 
-	/* kernel_fpu_begin/end is costly, use fallback for small updates */
-	if (srclen <= 288 || !crypto_simd_usable())
-		return crypto_poly1305_update(desc, src, srclen);
-
-	kernel_fpu_begin();
-
 	if (unlikely(dctx->buflen)) {
 		bytes = min(srclen, POLY1305_BLOCK_SIZE - dctx->buflen);
 		memcpy(dctx->buf + dctx->buflen, src, bytes);
@@ -147,12 +140,50 @@ static int poly1305_simd_update(struct shash_desc *desc,
 		srclen = bytes;
 	}
 
-	kernel_fpu_end();
-
 	if (unlikely(srclen)) {
 		dctx->buflen = srclen;
 		memcpy(dctx->buf, src, srclen);
 	}
+}
+
+static int poly1305_simd_update(struct shash_desc *desc,
+				const u8 *src, unsigned int srclen)
+{
+	/* kernel_fpu_begin/end is costly, use fallback for small updates */
+	if (srclen <= 288 || !crypto_simd_usable())
+		return crypto_poly1305_update(desc, src, srclen);
+
+	kernel_fpu_begin();
+	poly1305_simd_do_update(desc, src, srclen);
+	kernel_fpu_end();
+
+	return 0;
+}
+
+static int poly1305_simd_update_from_sg(struct shash_desc *desc,
+					struct scatterlist *sg,
+					unsigned int srclen,
+					int flags)
+{
+	bool do_simd = crypto_simd_usable() && srclen > 288;
+	struct crypto_hash_walk walk;
+	int nbytes;
+
+	if (do_simd) {
+		kernel_fpu_begin();
+		flags &= ~CRYPTO_TFM_REQ_MAY_SLEEP;
+	}
+
+	for (nbytes = crypto_shash_walk_sg(desc, sg, srclen, &walk, flags);
+	     nbytes > 0;
+	     nbytes = crypto_hash_walk_done(&walk, 0)) {
+		if (do_simd)
+			poly1305_simd_do_update(desc, walk.data, nbytes);
+		else
+			crypto_poly1305_update(desc, walk.data, nbytes);
+	}
+	if (do_simd)
+		kernel_fpu_end();
 
 	return 0;
 }
@@ -161,6 +192,7 @@ static struct shash_alg alg = {
 	.digestsize	= POLY1305_DIGEST_SIZE,
 	.init		= poly1305_simd_init,
 	.update		= poly1305_simd_update,
+	.update_from_sg	= poly1305_simd_update_from_sg,
 	.final		= crypto_poly1305_final,
 	.descsize	= sizeof(struct poly1305_simd_desc_ctx),
 	.base		= {
-- 
2.20.1