linux-kernel - [PATCH v3 03/21] crypto/arm64: sm4-ce-gcm - Avoid pointless yield of the NEON unit

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Message-ID: <20251008154533.3089255-26-ardb+git@google.com>
Date: Wed,  8 Oct 2025 17:45:37 +0200
From: Ard Biesheuvel <ardb+git@...gle.com>
To: linux-arm-kernel@...ts.infradead.org
Cc: linux-kernel@...r.kernel.org, linux-crypto@...r.kernel.org, 
	herbert@...dor.apana.org.au, ebiggers@...nel.org, 
	Ard Biesheuvel <ardb@...nel.org>
Subject: [PATCH v3 03/21] crypto/arm64: sm4-ce-gcm - Avoid pointless yield of
 the NEON unit

From: Ard Biesheuvel <ardb@...nel.org>

Kernel mode NEON sections are now preemptible on arm64, and so there is
no need to yield it when calling APIs that may sleep.

Also, move the calls to kernel_neon_end() to the same scope as
kernel_neon_begin(). This is needed for a subsequent change where a
stack buffer is allocated transparently and passed to
kernel_neon_begin().

While at it, simplify the logic.

Acked-by: Eric Biggers <ebiggers@...nel.org>
[ardb: Simplify convoluted logic]
Signed-off-by: Ard Biesheuvel <ardb@...nel.org>
---
 arch/arm64/crypto/sm4-ce-gcm-glue.c | 25 +++++---------------
 1 file changed, 6 insertions(+), 19 deletions(-)

diff --git a/arch/arm64/crypto/sm4-ce-gcm-glue.c b/arch/arm64/crypto/sm4-ce-gcm-glue.c
index c2ea3d5f690b..8f6fc8c33c3f 100644
--- a/arch/arm64/crypto/sm4-ce-gcm-glue.c
+++ b/arch/arm64/crypto/sm4-ce-gcm-glue.c
@@ -154,36 +154,23 @@ static int gcm_crypt(struct aead_request *req, struct skcipher_walk *walk,
 	if (req->assoclen)
 		gcm_calculate_auth_mac(req, ghash);
 
-	while (walk->nbytes) {
+	do {
 		unsigned int tail = walk->nbytes % SM4_BLOCK_SIZE;
 		const u8 *src = walk->src.virt.addr;
 		u8 *dst = walk->dst.virt.addr;
+		const u8 *l = NULL;
 
 		if (walk->nbytes == walk->total) {
-			sm4_ce_pmull_gcm_crypt(ctx->key.rkey_enc, dst, src, iv,
-					       walk->nbytes, ghash,
-					       ctx->ghash_table,
-					       (const u8 *)&lengths);
-
-			kernel_neon_end();
-
-			return skcipher_walk_done(walk, 0);
+			l = (const u8 *)&lengths;
+			tail = 0;
 		}
 
 		sm4_ce_pmull_gcm_crypt(ctx->key.rkey_enc, dst, src, iv,
 				       walk->nbytes - tail, ghash,
-				       ctx->ghash_table, NULL);
-
-		kernel_neon_end();
+				       ctx->ghash_table, l);
 
 		err = skcipher_walk_done(walk, tail);
-
-		kernel_neon_begin();
-	}
-
-	sm4_ce_pmull_gcm_crypt(ctx->key.rkey_enc, NULL, NULL, iv,
-			       walk->nbytes, ghash, ctx->ghash_table,
-			       (const u8 *)&lengths);
+	} while (walk->nbytes);
 
 	kernel_neon_end();
 
-- 
2.51.0.710.ga91ca5db03-goog