crypto: chacha20 - Add a four block SSSE3 variant for x86_64

Extends the x86_64 SSSE3 ChaCha20 implementation by a function processing
four ChaCha20 blocks in parallel. This avoids the word shuffling needed
in the single block variant, further increasing throughput.

For large messages, throughput increases by ~110% compared to single block
SSSE3:

testing speed of chacha20 (chacha20-simd) encryption
test 0 (256 bit key, 16 byte blocks): 43141886 operations in 10 seconds (690270176 bytes)
test 1 (256 bit key, 64 byte blocks): 46845874 operations in 10 seconds (2998135936 bytes)
test 2 (256 bit key, 256 byte blocks): 18458512 operations in 10 seconds (4725379072 bytes)
test 3 (256 bit key, 1024 byte blocks): 5360533 operations in 10 seconds (5489185792 bytes)
test 4 (256 bit key, 8192 byte blocks): 692846 operations in 10 seconds (5675794432 bytes)

testing speed of chacha20 (chacha20-simd) encryption
test 0 (256 bit key, 16 byte blocks): 42249230 operations in 10 seconds (675987680 bytes)
test 1 (256 bit key, 64 byte blocks): 46441641 operations in 10 seconds (2972265024 bytes)
test 2 (256 bit key, 256 byte blocks): 33028112 operations in 10 seconds (8455196672 bytes)
test 3 (256 bit key, 1024 byte blocks): 11568759 operations in 10 seconds (11846409216 bytes)
test 4 (256 bit key, 8192 byte blocks): 1448761 operations in 10 seconds (11868250112 bytes)

Benchmark results from a Core i5-4670T.
Signed-off-by: Martin Willi <martin@strongswan.org>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>

arch/x86/crypto/chacha20_glue.c

@@ -20,12 +20,20 @@
 #define CHACHA20_STATE_ALIGN 16
 
 asmlinkage void chacha20_block_xor_ssse3(u32 *state, u8 *dst, const u8 *src);
+asmlinkage void chacha20_4block_xor_ssse3(u32 *state, u8 *dst, const u8 *src);
 
 static void chacha20_dosimd(u32 *state, u8 *dst, const u8 *src,
 			    unsigned int bytes)
 {
 	u8 buf[CHACHA20_BLOCK_SIZE];
 
+	while (bytes >= CHACHA20_BLOCK_SIZE * 4) {
+		chacha20_4block_xor_ssse3(state, dst, src);
+		bytes -= CHACHA20_BLOCK_SIZE * 4;
+		src += CHACHA20_BLOCK_SIZE * 4;
+		dst += CHACHA20_BLOCK_SIZE * 4;
+		state[12] += 4;
+	}
 	while (bytes >= CHACHA20_BLOCK_SIZE) {
 		chacha20_block_xor_ssse3(state, dst, src);
 		bytes -= CHACHA20_BLOCK_SIZE;