[PATCH v2] crypto: arm/chacha-neon - optimize for non-block size multiples
Ard Biesheuvel
ardb at kernel.org
Tue Nov 3 11:28:09 EST 2020
The current NEON based ChaCha implementation for ARM is optimized for
multiples of 4x the ChaCha block size (64 bytes). This makes sense for
block encryption, but given that ChaCha is also often used in the
context of networking, it makes sense to consider arbitrary length
inputs as well.
For example, WireGuard typically uses 1420 byte packets, and performing
ChaCha encryption involves 5 invocations of chacha_4block_xor_neon()
and 3 invocations of chacha_block_xor_neon(), where the last one also
involves a memcpy() using a buffer on the stack to process the final
chunk of 1420 % 64 == 12 bytes.
Let's optimize for this case as well, by letting chacha_4block_xor_neon()
deal with any input size between 64 and 256 bytes, using NEON permutation
instructions and overlapping loads and stores. This way, the 140 byte
tail of a 1420 byte input buffer can simply be processed in one go.
This results in the following performance improvements for 1420 byte
blocks, without significant impact on power-of-2 input sizes. (Note
that Raspberry Pi is widely used in combination with a 32-bit kernel,
even though the core is 64-bit capable)
Cortex-A8 (BeagleBone) : 7%
Cortex-A15 (Calxeda Midway) : 21%
Cortex-A53 (Raspberry Pi 3) : 3%
Cortex-A72 (Raspberry Pi 4) : 19%
Cc: Eric Biggers <ebiggers at google.com>
Cc: "Jason A . Donenfeld" <Jason at zx2c4.com>
Signed-off-by: Ard Biesheuvel <ardb at kernel.org>
---
v2:
- avoid memcpy() if the residual byte count is exactly 64 bytes
- get rid of register based post increments, and simply rewind the src
pointer as needed (the dst pointer did not need the register post
increment in the first place)
- add benchmark results for 32-bit CPUs to commit log.
arch/arm/crypto/chacha-glue.c | 34 +++----
arch/arm/crypto/chacha-neon-core.S | 97 ++++++++++++++++++--
2 files changed, 107 insertions(+), 24 deletions(-)
diff --git a/arch/arm/crypto/chacha-glue.c b/arch/arm/crypto/chacha-glue.c
index 59da6c0b63b6..7b5cf8430c6d 100644
--- a/arch/arm/crypto/chacha-glue.c
+++ b/arch/arm/crypto/chacha-glue.c
@@ -23,7 +23,7 @@
asmlinkage void chacha_block_xor_neon(const u32 *state, u8 *dst, const u8 *src,
int nrounds);
asmlinkage void chacha_4block_xor_neon(const u32 *state, u8 *dst, const u8 *src,
- int nrounds);
+ int nrounds, unsigned int nbytes);
asmlinkage void hchacha_block_arm(const u32 *state, u32 *out, int nrounds);
asmlinkage void hchacha_block_neon(const u32 *state, u32 *out, int nrounds);
@@ -42,24 +42,24 @@ static void chacha_doneon(u32 *state, u8 *dst, const u8 *src,
{
u8 buf[CHACHA_BLOCK_SIZE];
- while (bytes >= CHACHA_BLOCK_SIZE * 4) {
- chacha_4block_xor_neon(state, dst, src, nrounds);
- bytes -= CHACHA_BLOCK_SIZE * 4;
- src += CHACHA_BLOCK_SIZE * 4;
- dst += CHACHA_BLOCK_SIZE * 4;
- state[12] += 4;
- }
- while (bytes >= CHACHA_BLOCK_SIZE) {
- chacha_block_xor_neon(state, dst, src, nrounds);
- bytes -= CHACHA_BLOCK_SIZE;
- src += CHACHA_BLOCK_SIZE;
- dst += CHACHA_BLOCK_SIZE;
- state[12]++;
+ while (bytes > CHACHA_BLOCK_SIZE) {
+ unsigned int l = min(bytes, CHACHA_BLOCK_SIZE * 4U);
+
+ chacha_4block_xor_neon(state, dst, src, nrounds, l);
+ bytes -= l;
+ src += l;
+ dst += l;
+ state[12] += DIV_ROUND_UP(l, CHACHA_BLOCK_SIZE);
}
if (bytes) {
- memcpy(buf, src, bytes);
- chacha_block_xor_neon(state, buf, buf, nrounds);
- memcpy(dst, buf, bytes);
+ const u8 *s = src;
+ u8 *d = dst;
+
+ if (bytes != CHACHA_BLOCK_SIZE)
+ s = d = memcpy(buf, src, bytes);
+ chacha_block_xor_neon(state, d, s, nrounds);
+ if (d != dst)
+ memcpy(dst, buf, bytes);
}
}
diff --git a/arch/arm/crypto/chacha-neon-core.S b/arch/arm/crypto/chacha-neon-core.S
index eb22926d4912..13d12f672656 100644
--- a/arch/arm/crypto/chacha-neon-core.S
+++ b/arch/arm/crypto/chacha-neon-core.S
@@ -47,6 +47,7 @@
*/
#include <linux/linkage.h>
+#include <asm/cache.h>
.text
.fpu neon
@@ -205,7 +206,7 @@ ENDPROC(hchacha_block_neon)
.align 5
ENTRY(chacha_4block_xor_neon)
- push {r4-r5}
+ push {r4, lr}
mov r4, sp // preserve the stack pointer
sub ip, sp, #0x20 // allocate a 32 byte buffer
bic ip, ip, #0x1f // aligned to 32 bytes
@@ -229,10 +230,10 @@ ENTRY(chacha_4block_xor_neon)
vld1.32 {q0-q1}, [r0]
vld1.32 {q2-q3}, [ip]
- adr r5, .Lctrinc
+ adr lr, .Lctrinc
vdup.32 q15, d7[1]
vdup.32 q14, d7[0]
- vld1.32 {q4}, [r5, :128]
+ vld1.32 {q4}, [lr, :128]
vdup.32 q13, d6[1]
vdup.32 q12, d6[0]
vdup.32 q11, d5[1]
@@ -455,7 +456,7 @@ ENTRY(chacha_4block_xor_neon)
// Re-interleave the words in the first two rows of each block (x0..7).
// Also add the counter values 0-3 to x12[0-3].
- vld1.32 {q8}, [r5, :128] // load counter values 0-3
+ vld1.32 {q8}, [lr, :128] // load counter values 0-3
vzip.32 q0, q1 // => (0 1 0 1) (0 1 0 1)
vzip.32 q2, q3 // => (2 3 2 3) (2 3 2 3)
vzip.32 q4, q5 // => (4 5 4 5) (4 5 4 5)
@@ -493,6 +494,8 @@ ENTRY(chacha_4block_xor_neon)
// Re-interleave the words in the last two rows of each block (x8..15).
vld1.32 {q8-q9}, [sp, :256]
+ mov sp, r4 // restore original stack pointer
+ ldr r4, [r4, #8] // load number of bytes
vzip.32 q12, q13 // => (12 13 12 13) (12 13 12 13)
vzip.32 q14, q15 // => (14 15 14 15) (14 15 14 15)
vzip.32 q8, q9 // => (8 9 8 9) (8 9 8 9)
@@ -520,41 +523,121 @@ ENTRY(chacha_4block_xor_neon)
// XOR the rest of the data with the keystream
vld1.8 {q0-q1}, [r2]!
+ subs r4, r4, #96
veor q0, q0, q8
veor q1, q1, q12
+ ble .Lle96
vst1.8 {q0-q1}, [r1]!
vld1.8 {q0-q1}, [r2]!
+ subs r4, r4, #32
veor q0, q0, q2
veor q1, q1, q6
+ ble .Lle128
vst1.8 {q0-q1}, [r1]!
vld1.8 {q0-q1}, [r2]!
+ subs r4, r4, #32
veor q0, q0, q10
veor q1, q1, q14
+ ble .Lle160
vst1.8 {q0-q1}, [r1]!
vld1.8 {q0-q1}, [r2]!
+ subs r4, r4, #32
veor q0, q0, q4
veor q1, q1, q5
+ ble .Lle192
vst1.8 {q0-q1}, [r1]!
vld1.8 {q0-q1}, [r2]!
+ subs r4, r4, #32
veor q0, q0, q9
veor q1, q1, q13
+ ble .Lle224
vst1.8 {q0-q1}, [r1]!
vld1.8 {q0-q1}, [r2]!
+ subs r4, r4, #32
veor q0, q0, q3
veor q1, q1, q7
+ blt .Llt256
+.Lout:
vst1.8 {q0-q1}, [r1]!
vld1.8 {q0-q1}, [r2]
- mov sp, r4 // restore original stack pointer
veor q0, q0, q11
veor q1, q1, q15
vst1.8 {q0-q1}, [r1]
- pop {r4-r5}
- bx lr
+ pop {r4, pc}
+
+.Lle192:
+ vmov q4, q9
+ vmov q5, q13
+
+.Lle160:
+ // nothing to do
+
+.Lfinalblock:
+ // Process the final block if processing less than 4 full blocks.
+ // Entered with 32 bytes of ChaCha cipher stream in q4-q5, and the
+ // previous 32 byte output block that still needs to be written at
+ // [r1] in q0-q1.
+ beq .Lfullblock
+
+.Lpartialblock:
+ adr lr, .Lpermute + 32
+ add r2, r2, r4
+ add lr, lr, r4
+ add r4, r4, r1
+
+ vld1.8 {q2-q3}, [lr]
+ vld1.8 {q6-q7}, [r2]
+
+ add r4, r4, #32
+
+ vtbl.8 d4, {q4-q5}, d4
+ vtbl.8 d5, {q4-q5}, d5
+ vtbl.8 d6, {q4-q5}, d6
+ vtbl.8 d7, {q4-q5}, d7
+
+ veor q6, q6, q2
+ veor q7, q7, q3
+
+ vst1.8 {q6-q7}, [r4] // overlapping stores
+ vst1.8 {q0-q1}, [r1]
+ pop {r4, pc}
+
+.Lfullblock:
+ vmov q11, q4
+ vmov q15, q5
+ b .Lout
+.Lle96:
+ vmov q4, q2
+ vmov q5, q6
+ b .Lfinalblock
+.Lle128:
+ vmov q4, q10
+ vmov q5, q14
+ b .Lfinalblock
+.Lle224:
+ vmov q4, q3
+ vmov q5, q7
+ b .Lfinalblock
+.Llt256:
+ vmov q4, q11
+ vmov q5, q15
+ b .Lpartialblock
ENDPROC(chacha_4block_xor_neon)
+
+ .align L1_CACHE_SHIFT
+.Lpermute:
+ .byte 0x00, 0x01, 0x02, 0x03, 0x04, 0x05, 0x06, 0x07
+ .byte 0x08, 0x09, 0x0a, 0x0b, 0x0c, 0x0d, 0x0e, 0x0f
+ .byte 0x10, 0x11, 0x12, 0x13, 0x14, 0x15, 0x16, 0x17
+ .byte 0x18, 0x19, 0x1a, 0x1b, 0x1c, 0x1d, 0x1e, 0x1f
+ .byte 0x00, 0x01, 0x02, 0x03, 0x04, 0x05, 0x06, 0x07
+ .byte 0x08, 0x09, 0x0a, 0x0b, 0x0c, 0x0d, 0x0e, 0x0f
+ .byte 0x10, 0x11, 0x12, 0x13, 0x14, 0x15, 0x16, 0x17
+ .byte 0x18, 0x19, 0x1a, 0x1b, 0x1c, 0x1d, 0x1e, 0x1f
--
2.17.1
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