diff mbox series

[v2,10/19] crypto: arm64/sha256-neon - play nice with CONFIG_PREEMPT kernels

Message ID 20171204122645.31535-11-ard.biesheuvel@linaro.org
State Superseded
Headers show
Series None | expand

Commit Message

Ard Biesheuvel Dec. 4, 2017, 12:26 p.m. UTC 
Tweak the SHA256 update routines to invoke the SHA256 block transform
block by block, to avoid excessive scheduling delays caused by the
NEON algorithm running with preemption disabled.

Also, remove a stale comment which no longer applies now that kernel
mode NEON is actually disallowed in some contexts.

Signed-off-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>

---
 arch/arm64/crypto/sha256-glue.c | 36 +++++++++++++-------
 1 file changed, 23 insertions(+), 13 deletions(-)

-- 
2.11.0
diff mbox series

Patch

diff --git a/arch/arm64/crypto/sha256-glue.c b/arch/arm64/crypto/sha256-glue.c
index b064d925fe2a..e8880ccdc71f 100644
--- a/arch/arm64/crypto/sha256-glue.c
+++ b/arch/arm64/crypto/sha256-glue.c
@@ -89,21 +89,32 @@  static struct shash_alg algs[] = { {
 static int sha256_update_neon(struct shash_desc *desc, const u8 *data,
 			      unsigned int len)
 {
-	/*
-	 * Stacking and unstacking a substantial slice of the NEON register
-	 * file may significantly affect performance for small updates when
-	 * executing in interrupt context, so fall back to the scalar code
-	 * in that case.
-	 */
+	struct sha256_state *sctx = shash_desc_ctx(desc);
+
 	if (!may_use_simd())
 		return sha256_base_do_update(desc, data, len,
 				(sha256_block_fn *)sha256_block_data_order);
 
-	kernel_neon_begin();
-	sha256_base_do_update(desc, data, len,
-				(sha256_block_fn *)sha256_block_neon);
-	kernel_neon_end();
+	while (len > 0) {
+		unsigned int chunk = len;
+
+		/*
+		 * Don't hog the CPU for the entire time it takes to process all
+		 * input when running on a preemptible kernel, but process the
+		 * data block by block instead.
+		 */
+		if (IS_ENABLED(CONFIG_PREEMPT) &&
+		    chunk + sctx->count % SHA256_BLOCK_SIZE > SHA256_BLOCK_SIZE)
+			chunk = SHA256_BLOCK_SIZE -
+				sctx->count % SHA256_BLOCK_SIZE;
 
+		kernel_neon_begin();
+		sha256_base_do_update(desc, data, chunk,
+				      (sha256_block_fn *)sha256_block_neon);
+		kernel_neon_end();
+		data += chunk;
+		len -= chunk;
+	}
 	return 0;
 }
 
@@ -117,10 +128,9 @@  static int sha256_finup_neon(struct shash_desc *desc, const u8 *data,
 		sha256_base_do_finalize(desc,
 				(sha256_block_fn *)sha256_block_data_order);
 	} else {
-		kernel_neon_begin();
 		if (len)
-			sha256_base_do_update(desc, data, len,
-				(sha256_block_fn *)sha256_block_neon);
+			sha256_update_neon(desc, data, len);
+		kernel_neon_begin();
 		sha256_base_do_finalize(desc,
 				(sha256_block_fn *)sha256_block_neon);
 		kernel_neon_end();