crypto: arm64/aes-blk - improve XTS mask handling

The Crypto Extension instantiation of the aes-modes.S collection of
skciphers uses only 15 NEON registers for the round key array, whereas
the pure NEON flavor uses 16 NEON registers for the AES S-box.

This means we have a spare register available that we can use to hold
the XTS mask vector, removing the need to reload it at every iteration
of the inner loop.

Since the pure NEON version does not permit this optimization, tweak
the macros so we can factor out this functionality. Also, replace the
literal load with a short sequence to compose the mask vector.

On Cortex-A53, this results in a ~4% speedup.
Signed-off-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>

arch/arm64/crypto/aes-ce.S

@@ -17,6 +17,11 @@
 
 	.arch		armv8-a+crypto
 
+	xtsmask		.req	v16
+
+	.macro		xts_reload_mask, tmp
+	.endm
+
 	/* preload all round keys */
 	.macro		load_round_keys, rounds, rk
 	cmp		\rounds, #12

arch/arm64/crypto/aes-modes.S

@@ -340,17 +340,19 @@ AES_ENDPROC(aes_ctr_encrypt)
 	 *		   int blocks, u8 const rk2[], u8 iv[], int first)
 	 */
 
-	.macro		next_tweak, out, in, const, tmp
+	.macro		next_tweak, out, in, tmp
 	sshr		\tmp\().2d,  \in\().2d,   #63
-	and		\tmp\().16b, \tmp\().16b, \const\().16b
+	and		\tmp\().16b, \tmp\().16b, xtsmask.16b
 	add		\out\().2d,  \in\().2d,   \in\().2d
 	ext		\tmp\().16b, \tmp\().16b, \tmp\().16b, #8
 	eor		\out\().16b, \out\().16b, \tmp\().16b
 	.endm
 
-.Lxts_mul_x:
-CPU_LE(	.quad		1, 0x87		)
-CPU_BE(	.quad		0x87, 1		)
+	.macro		xts_load_mask, tmp
+	movi		xtsmask.2s, #0x1
+	movi		\tmp\().2s, #0x87
+	uzp1		xtsmask.4s, xtsmask.4s, \tmp\().4s
+	.endm
 
 AES_ENTRY(aes_xts_encrypt)
 	stp		x29, x30, [sp, #-16]!
@@ -362,24 +364,24 @@ AES_ENTRY(aes_xts_encrypt)
 	enc_prepare	w3, x5, x8
 	encrypt_block	v4, w3, x5, x8, w7		/* first tweak */
 	enc_switch_key	w3, x2, x8
-	ldr		q7, .Lxts_mul_x
+	xts_load_mask	v8
 	b		.LxtsencNx
 
 .Lxtsencnotfirst:
 	enc_prepare	w3, x2, x8
 .LxtsencloopNx:
-	ldr		q7, .Lxts_mul_x
-	next_tweak	v4, v4, v7, v8
+	xts_reload_mask	v8
+	next_tweak	v4, v4, v8
 .LxtsencNx:
 	subs		w4, w4, #4
 	bmi		.Lxtsenc1x
 	ld1		{v0.16b-v3.16b}, [x1], #64	/* get 4 pt blocks */
-	next_tweak	v5, v4, v7, v8
+	next_tweak	v5, v4, v8
 	eor		v0.16b, v0.16b, v4.16b
-	next_tweak	v6, v5, v7, v8
+	next_tweak	v6, v5, v8
 	eor		v1.16b, v1.16b, v5.16b
 	eor		v2.16b, v2.16b, v6.16b
-	next_tweak	v7, v6, v7, v8
+	next_tweak	v7, v6, v8
 	eor		v3.16b, v3.16b, v7.16b
 	bl		aes_encrypt_block4x
 	eor		v3.16b, v3.16b, v7.16b
@@ -401,7 +403,7 @@ AES_ENTRY(aes_xts_encrypt)
 	st1		{v0.16b}, [x0], #16
 	subs		w4, w4, #1
 	beq		.Lxtsencout
-	next_tweak	v4, v4, v7, v8
+	next_tweak	v4, v4, v8
 	b		.Lxtsencloop
 .Lxtsencout:
 	st1		{v4.16b}, [x6]
@@ -420,24 +422,24 @@ AES_ENTRY(aes_xts_decrypt)
 	enc_prepare	w3, x5, x8
 	encrypt_block	v4, w3, x5, x8, w7		/* first tweak */
 	dec_prepare	w3, x2, x8
-	ldr		q7, .Lxts_mul_x
+	xts_load_mask	v8
 	b		.LxtsdecNx
 
 .Lxtsdecnotfirst:
 	dec_prepare	w3, x2, x8
 .LxtsdecloopNx:
-	ldr		q7, .Lxts_mul_x
-	next_tweak	v4, v4, v7, v8
+	xts_reload_mask	v8
+	next_tweak	v4, v4, v8
 .LxtsdecNx:
 	subs		w4, w4, #4
 	bmi		.Lxtsdec1x
 	ld1		{v0.16b-v3.16b}, [x1], #64	/* get 4 ct blocks */
-	next_tweak	v5, v4, v7, v8
+	next_tweak	v5, v4, v8
 	eor		v0.16b, v0.16b, v4.16b
-	next_tweak	v6, v5, v7, v8
+	next_tweak	v6, v5, v8
 	eor		v1.16b, v1.16b, v5.16b
 	eor		v2.16b, v2.16b, v6.16b
-	next_tweak	v7, v6, v7, v8
+	next_tweak	v7, v6, v8
 	eor		v3.16b, v3.16b, v7.16b
 	bl		aes_decrypt_block4x
 	eor		v3.16b, v3.16b, v7.16b
@@ -459,7 +461,7 @@ AES_ENTRY(aes_xts_decrypt)
 	st1		{v0.16b}, [x0], #16
 	subs		w4, w4, #1
 	beq		.Lxtsdecout
-	next_tweak	v4, v4, v7, v8
+	next_tweak	v4, v4, v8
 	b		.Lxtsdecloop
 .Lxtsdecout:
 	st1		{v4.16b}, [x6]

arch/arm64/crypto/aes-neon.S

@@ -14,6 +14,12 @@
 #define AES_ENTRY(func)		ENTRY(neon_ ## func)
 #define AES_ENDPROC(func)	ENDPROC(neon_ ## func)
 
+	xtsmask		.req	v7
+
+	.macro		xts_reload_mask, tmp
+	xts_load_mask	\tmp
+	.endm
+
 	/* multiply by polynomial 'x' in GF(2^8) */
 	.macro		mul_by_x, out, in, temp, const
 	sshr		\temp, \in, #7