linux-kernel - [PATCH 3/5] crypto/arm64: sm4-ce-gcm - Avoid pointless yield of the NEON unit

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Message-ID: <20250918063539.2640512-10-ardb+git@google.com>
Date: Thu, 18 Sep 2025 08:35:43 +0200
From: Ard Biesheuvel <ardb+git@...gle.com>
To: linux-arm-kernel@...ts.infradead.org
Cc: linux-crypto@...r.kernel.org, linux-kernel@...r.kernel.org, 
	herbert@...dor.apana.org.au, ebiggers@...nel.org, 
	Ard Biesheuvel <ardb@...nel.org>, Marc Zyngier <maz@...nel.org>, Will Deacon <will@...nel.org>, 
	Mark Rutland <mark.rutland@....com>, Kees Cook <keescook@...omium.org>, 
	Catalin Marinas <catalin.marinas@....com>, Mark Brown <broonie@...nel.org>
Subject: [PATCH 3/5] 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().

Signed-off-by: Ard Biesheuvel <ardb@...nel.org>
---
 arch/arm64/crypto/sm4-ce-gcm-glue.c | 10 +++-------
 1 file changed, 3 insertions(+), 7 deletions(-)

diff --git a/arch/arm64/crypto/sm4-ce-gcm-glue.c b/arch/arm64/crypto/sm4-ce-gcm-glue.c
index c2ea3d5f690b..170cd0151385 100644
--- a/arch/arm64/crypto/sm4-ce-gcm-glue.c
+++ b/arch/arm64/crypto/sm4-ce-gcm-glue.c
@@ -165,26 +165,22 @@ static int gcm_crypt(struct aead_request *req, struct skcipher_walk *walk,
 					       ctx->ghash_table,
 					       (const u8 *)&lengths);
 
-			kernel_neon_end();
-
-			return skcipher_walk_done(walk, 0);
+			err = skcipher_walk_done(walk, 0);
+			goto out;
 		}
 
 		sm4_ce_pmull_gcm_crypt(ctx->key.rkey_enc, dst, src, iv,
 				       walk->nbytes - tail, ghash,
 				       ctx->ghash_table, NULL);
 
-		kernel_neon_end();
-
 		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);
 
+out:
 	kernel_neon_end();
 
 	return err;
-- 
2.51.0.384.g4c02a37b29-goog