linux-kernel - [PATCH 2/5] crypto/arm64: sm4-ce-ccm - Avoid pointless yield of the NEON unit

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Message-ID: <20250918063539.2640512-9-ardb+git@google.com>
Date: Thu, 18 Sep 2025 08:35:42 +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 2/5] crypto/arm64: sm4-ce-ccm - 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-ccm-glue.c | 10 ++--------
 1 file changed, 2 insertions(+), 8 deletions(-)

diff --git a/arch/arm64/crypto/sm4-ce-ccm-glue.c b/arch/arm64/crypto/sm4-ce-ccm-glue.c
index e9cc1c1364ec..f9771ab2a05f 100644
--- a/arch/arm64/crypto/sm4-ce-ccm-glue.c
+++ b/arch/arm64/crypto/sm4-ce-ccm-glue.c
@@ -179,11 +179,7 @@ static int ccm_crypt(struct aead_request *req, struct skcipher_walk *walk,
 				 walk->src.virt.addr, walk->iv,
 				 walk->nbytes - tail, mac);
 
-		kernel_neon_end();
-
 		err = skcipher_walk_done(walk, tail);
-
-		kernel_neon_begin();
 	}
 
 	if (walk->nbytes) {
@@ -193,15 +189,13 @@ static int ccm_crypt(struct aead_request *req, struct skcipher_walk *walk,
 
 		sm4_ce_ccm_final(rkey_enc, ctr0, mac);
 
-		kernel_neon_end();
-
 		err = skcipher_walk_done(walk, 0);
 	} else {
 		sm4_ce_ccm_final(rkey_enc, ctr0, mac);
-
-		kernel_neon_end();
 	}
 
+	kernel_neon_end();
+
 	return err;
 }
 
-- 
2.51.0.384.g4c02a37b29-goog