crypto: arm64/aes-ccm - reduce NEON begin/end calls for common case

AES-CCM (as used in WPA2 CCMP, for instance) typically involves
authenticate-only data, and operates on a single network packet, and so
the common case is for the authenticate, en/decrypt and finalize SIMD
helpers to all be called exactly once in sequence. Since
kernel_neon_end() now involves manipulation of the preemption state as
well as the softirq mask state, let's reduce the number of times we are
forced to call it to only once if we are handling this common case.
Signed-off-by: Ard Biesheuvel <ardb@kernel.org>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>

arch/arm64/crypto/aes-ce-ccm-core.S

@@ -124,6 +124,7 @@ SYM_FUNC_START(ce_aes_ccm_final)
 SYM_FUNC_END(ce_aes_ccm_final)
 
 	.macro	aes_ccm_do_crypt,enc
+	cbz	x2, 5f
 	ldr	x8, [x6, #8]			/* load lower ctr */
 	ld1	{v0.16b}, [x5]			/* load mac */
 CPU_LE(	rev	x8, x8			)	/* keep swabbed ctr in reg */

arch/arm64/crypto/aes-ce-ccm-glue.c

@@ -97,10 +97,8 @@ static int ccm_init_mac(struct aead_request *req, u8 maciv[], u32 msglen)
 static void ccm_update_mac(struct crypto_aes_ctx *key, u8 mac[], u8 const in[],
 			   u32 abytes, u32 *macp)
 {
-	kernel_neon_begin();
 	ce_aes_ccm_auth_data(mac, in, abytes, macp, key->key_enc,
 			     num_rounds(key));
-	kernel_neon_end();
 }
 
 static void ccm_calculate_auth_mac(struct aead_request *req, u8 mac[])
@@ -136,6 +134,12 @@ static void ccm_calculate_auth_mac(struct aead_request *req, u8 mac[])
 		n = min_t(u32, n, SZ_4K); /* yield NEON at least every 4k */
 		p = scatterwalk_map(&walk);
 		ccm_update_mac(ctx, mac, p, n, &macp);
+
+		if (len / SZ_4K > (len - n) / SZ_4K) {
+			kernel_neon_end();
+			kernel_neon_begin();
+		}
+
 		len -= n;
 
 		scatterwalk_unmap(p);
@@ -158,35 +162,41 @@ static int ccm_encrypt(struct aead_request *req)
 	if (err)
 		return err;
 
-	if (req->assoclen)
-		ccm_calculate_auth_mac(req, mac);
-
 	/* preserve the original iv for the final round */
 	memcpy(buf, req->iv, AES_BLOCK_SIZE);
 
 	err = skcipher_walk_aead_encrypt(&walk, req, false);
+	if (unlikely(err))
+		return err;
+
+	kernel_neon_begin();
 
-	while (walk.nbytes) {
+	if (req->assoclen)
+		ccm_calculate_auth_mac(req, mac);
+
+	do {
 		u32 tail = walk.nbytes % AES_BLOCK_SIZE;
 
 		if (walk.nbytes == walk.total)
 			tail = 0;
 
-		kernel_neon_begin();
 		ce_aes_ccm_encrypt(walk.dst.virt.addr, walk.src.virt.addr,
 				   walk.nbytes - tail, ctx->key_enc,
 				   num_rounds(ctx), mac, walk.iv);
+
+		if (walk.nbytes == walk.total)
+			ce_aes_ccm_final(mac, buf, ctx->key_enc, num_rounds(ctx));
+
 		kernel_neon_end();
 
+		if (walk.nbytes) {
 			err = skcipher_walk_done(&walk, tail);
-	}
-	if (!err) {
+			if (unlikely(err))
+				return err;
+			if (unlikely(walk.nbytes))
 				kernel_neon_begin();
-		ce_aes_ccm_final(mac, buf, ctx->key_enc, num_rounds(ctx));
-		kernel_neon_end();
 		}
-	if (err)
-		return err;
+	} while (walk.nbytes);
 
 	/* copy authtag to end of dst */
 	scatterwalk_map_and_copy(mac, req->dst, req->assoclen + req->cryptlen,
@@ -210,35 +220,41 @@ static int ccm_decrypt(struct aead_request *req)
 	if (err)
 		return err;
 
-	if (req->assoclen)
-		ccm_calculate_auth_mac(req, mac);
-
 	/* preserve the original iv for the final round */
 	memcpy(buf, req->iv, AES_BLOCK_SIZE);
 
 	err = skcipher_walk_aead_decrypt(&walk, req, false);
+	if (unlikely(err))
+		return err;
+
+	kernel_neon_begin();
+
+	if (req->assoclen)
+		ccm_calculate_auth_mac(req, mac);
 
-	while (walk.nbytes) {
+	do {
 		u32 tail = walk.nbytes % AES_BLOCK_SIZE;
 
 		if (walk.nbytes == walk.total)
 			tail = 0;
 
-		kernel_neon_begin();
 		ce_aes_ccm_decrypt(walk.dst.virt.addr, walk.src.virt.addr,
 				   walk.nbytes - tail, ctx->key_enc,
 				   num_rounds(ctx), mac, walk.iv);
+
+		if (walk.nbytes == walk.total)
+			ce_aes_ccm_final(mac, buf, ctx->key_enc, num_rounds(ctx));
+
 		kernel_neon_end();
 
+		if (walk.nbytes) {
 			err = skcipher_walk_done(&walk, tail);
-	}
-	if (!err) {
+			if (unlikely(err))
+				return err;
+			if (unlikely(walk.nbytes))
 				kernel_neon_begin();
-		ce_aes_ccm_final(mac, buf, ctx->key_enc, num_rounds(ctx));
-		kernel_neon_end();
 		}
-	if (err)
-		return err;
+	} while (walk.nbytes);
 
 	/* compare calculated auth tag with the stored one */
 	scatterwalk_map_and_copy(buf, req->src,