[PATCH 2/2] arm64/crc32: Implement 4-way interleave using PMULL

From: Ard Biesheuvel
Date: Tue Oct 15 2024 - 06:42:33 EST

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From: Ard Biesheuvel <ardb@xxxxxxxxxx>

Now that kernel mode NEON no longer disables preemption, using FP/SIMD
in library code which is not obviously part of the crypto subsystem is
no longer problematic, as it will no longer incur unexpected latencies.

So accelerate the CRC-32 library code on arm64 to use a 4-way
interleave, using PMULL instructions to implement the folding.

On Apple M2, this results in a speedup of 2 - 2.8x when using input
sizes of 1k - 8k. For smaller sizes, the overhead of preserving and
restoring the FP/SIMD register file may not be worth it, so 1k is used
as a threshold for choosing this code path.

The coefficient tables were generated using code provided by Eric. [0]

[0] https://github.com/ebiggers/libdeflate/blob/master/scripts/gen_crc32_multipliers.c

Cc: Eric Biggers <ebiggers@xxxxxxxxxx>
Signed-off-by: Ard Biesheuvel <ardb@xxxxxxxxxx>
---
arch/arm64/lib/Makefile | 2 +-
arch/arm64/lib/crc32-glue.c | 36 +++
arch/arm64/lib/crc32-pmull.S | 240 ++++++++++++++++++++
3 files changed, 277 insertions(+), 1 deletion(-)

diff --git a/arch/arm64/lib/Makefile b/arch/arm64/lib/Makefile
index 8e882f479d98..0ececb40fe40 100644
--- a/arch/arm64/lib/Makefile
+++ b/arch/arm64/lib/Makefile
@@ -13,7 +13,7 @@ endif

lib-$(CONFIG_ARCH_HAS_UACCESS_FLUSHCACHE) += uaccess_flushcache.o

-obj-$(CONFIG_CRC32) += crc32.o crc32-glue.o
+obj-$(CONFIG_CRC32) += crc32.o crc32-glue.o crc32-pmull.o

obj-$(CONFIG_FUNCTION_ERROR_INJECTION) += error-inject.o

diff --git a/arch/arm64/lib/crc32-glue.c b/arch/arm64/lib/crc32-glue.c
index 0b51761d4b75..bc5a13725394 100644
--- a/arch/arm64/lib/crc32-glue.c
+++ b/arch/arm64/lib/crc32-glue.c
@@ -4,16 +4,36 @@
#include <linux/linkage.h>

#include <asm/alternative.h>
+#include <asm/cpufeature.h>
+#include <asm/neon.h>
+#include <asm/simd.h>
+
+#include <crypto/internal/simd.h>
+
+// The minimum input length to consider the 4-way interleaved code path
+static const size_t min_len = 1024;

asmlinkage u32 crc32_le_arm64(u32 crc, unsigned char const *p, size_t len);
asmlinkage u32 crc32c_le_arm64(u32 crc, unsigned char const *p, size_t len);
asmlinkage u32 crc32_be_arm64(u32 crc, unsigned char const *p, size_t len);

+asmlinkage u32 crc32_le_pmull(u32 crc, unsigned char const *p, size_t len);
+asmlinkage u32 crc32c_le_pmull(u32 crc, unsigned char const *p, size_t len);
+asmlinkage u32 crc32_be_pmull(u32 crc, unsigned char const *p, size_t len);
+
u32 __pure crc32_le(u32 crc, unsigned char const *p, size_t len)
{
if (!alternative_has_cap_likely(ARM64_HAS_CRC32))
return crc32_le_base(crc, p, len);

+ if (len >= min_len && cpu_have_named_feature(PMULL) && crypto_simd_usable()) {
+ kernel_neon_begin();
+ crc = crc32_le_pmull(crc, p, len);
+ p += round_down(len, 64);
+ len %= 64;
+ kernel_neon_end();
+ }
+
return crc32_le_arm64(crc, p, len);
}

@@ -22,6 +42,14 @@ u32 __pure __crc32c_le(u32 crc, unsigned char const *p, size_t len)
if (!alternative_has_cap_likely(ARM64_HAS_CRC32))
return __crc32c_le_base(crc, p, len);

+ if (len >= min_len && cpu_have_named_feature(PMULL) && crypto_simd_usable()) {
+ kernel_neon_begin();
+ crc = crc32c_le_pmull(crc, p, len);
+ p += round_down(len, 64);
+ len %= 64;
+ kernel_neon_end();
+ }
+
return crc32c_le_arm64(crc, p, len);
}

@@ -30,5 +58,13 @@ u32 __pure crc32_be(u32 crc, unsigned char const *p, size_t len)
if (!alternative_has_cap_likely(ARM64_HAS_CRC32))
return crc32_be_base(crc, p, len);

+ if (len >= min_len && cpu_have_named_feature(PMULL) && crypto_simd_usable()) {
+ kernel_neon_begin();
+ crc = crc32_be_pmull(crc, p, len);
+ p += round_down(len, 64);
+ len %= 64;
+ kernel_neon_end();
+ }
+
return crc32_be_arm64(crc, p, len);
}
diff --git a/arch/arm64/lib/crc32-pmull.S b/arch/arm64/lib/crc32-pmull.S
new file mode 100644
index 000000000000..67c1baf18f41
--- /dev/null
+++ b/arch/arm64/lib/crc32-pmull.S
@@ -0,0 +1,240 @@
+// SPDX-License-Identifier: GPL-2.0-only
+// Copyright 2024 Google LLC
+// Author: Ard Biesheuvel <ardb@xxxxxxxxxx>
+
+#include <linux/linkage.h>
+#include <asm/assembler.h>
+
+ crc .req w0
+ xcrc .req x0
+ inp .req x1
+ len .req w2
+
+ .macro nop, reg0, reg1
+ .endm
+
+ .macro crc4way, insn, table, rev=nop, rbit=nop
+ /* Process up to 64 blocks of 64 bytes at a time */
+.La\@: mov w3, #64
+ lsr w4, len, #6
+ cmp len, #64 << 6
+ csel w3, w3, w4, ge
+ sub len, len, w3, lsl #6
+
+ /* Load the folding coefficients from the lookup table */
+ adr_l x4, \table - 12
+ add x4, x4, x3, lsl #3
+ add x4, x4, x3, lsl #2
+ ldp s0, s1, [x4]
+ ldr s2, [x4, #8]
+
+ /* Zero init partial CRCs for this iteration */
+ mov w4, #0
+ mov w5, #0
+ mov w6, #0
+
+ /* Divide the input into 4 contiguous blocks */
+ add x7, inp, x3, lsl #4
+ add x8, inp, x3, lsl #5
+ add x9, inp, x3, lsl #4
+ add x9, x9, x3, lsl #5
+ b .Lc\@
+
+.Lb\@: \insn w6, w6, x17
+.Lc\@: sub w3, w3, #1
+ ldp x10, x11, [inp], #16
+ ldp x12, x13, [x7], #16
+ ldp x14, x15, [x8], #16
+ ldp x16, x17, [x9], #16
+
+ \rev x10, x10
+ \rev x11, x11
+ \rev x12, x12
+ \rev x13, x13
+ \rev x14, x14
+ \rev x15, x15
+ \rev x16, x16
+ \rev x17, x17
+
+ \rbit x10, x10
+ \rbit x11, x11
+ \rbit x12, x12
+ \rbit x13, x13
+ \rbit x14, x14
+ \rbit x15, x15
+ \rbit x16, x16
+ \rbit x17, x17
+
+ /* Apply the CRC transform to 4 16-byte blocks in parallel */
+ \insn crc, crc, x10
+ \insn w4, w4, x12
+ \insn w5, w5, x14
+ \insn w6, w6, x16
+ \insn crc, crc, x11
+ \insn w4, w4, x13
+ \insn w5, w5, x15
+ cbnz w3, .Lb\@
+
+ /* Combine the 4 partial results */
+ mov v3.d[0], xcrc
+ mov v4.d[0], x4
+ mov v5.d[0], x5
+ pmull v0.1q, v0.1d, v3.1d
+ pmull v1.1q, v1.1d, v4.1d
+ pmull v2.1q, v2.1d, v5.1d
+ eor v0.8b, v0.8b, v1.8b
+ eor v0.8b, v0.8b, v2.8b
+ mov x5, v0.d[0]
+ eor x5, x5, x17
+ \insn crc, w6, x5
+
+ mov inp, x9
+ cmp len, #64
+ b.ge .La\@
+ ret
+ .endm
+
+ .cpu generic+crc+crypto
+SYM_FUNC_START(crc32c_le_pmull)
+ crc4way crc32cx, .L0 CPU_BE(, rev)
+SYM_FUNC_END(crc32c_le_pmull)
+
+SYM_FUNC_START(crc32_le_pmull)
+ crc4way crc32x, .L1 CPU_BE(, rev)
+SYM_FUNC_END(crc32_le_pmull)
+
+SYM_FUNC_START(crc32_be_pmull)
+ crc4way crc32x, .L1 CPU_LE(, rev), rbit=rbit
+SYM_FUNC_END(crc32_be_pmull)
+
+ .section .rodata, "a", %progbits
+ .align 6
+.L0: .long 0xddc0152b, 0xba4fc28e, 0x493c7d27
+ .long 0x0715ce53, 0x9e4addf8, 0xba4fc28e
+ .long 0xc96cfdc0, 0x0715ce53, 0xddc0152b
+ .long 0xab7aff2a, 0x0d3b6092, 0x9e4addf8
+ .long 0x299847d5, 0x878a92a7, 0x39d3b296
+ .long 0xb6dd949b, 0xab7aff2a, 0x0715ce53
+ .long 0xa60ce07b, 0x83348832, 0x47db8317
+ .long 0xd270f1a2, 0xb9e02b86, 0x0d3b6092
+ .long 0x65863b64, 0xb6dd949b, 0xc96cfdc0
+ .long 0xb3e32c28, 0xbac2fd7b, 0x878a92a7
+ .long 0xf285651c, 0xce7f39f4, 0xdaece73e
+ .long 0x271d9844, 0xd270f1a2, 0xab7aff2a
+ .long 0x6cb08e5c, 0x2b3cac5d, 0x2162d385
+ .long 0xcec3662e, 0x1b03397f, 0x83348832
+ .long 0x8227bb8a, 0xb3e32c28, 0x299847d5
+ .long 0xd7a4825c, 0xdd7e3b0c, 0xb9e02b86
+ .long 0xf6076544, 0x10746f3c, 0x18b33a4e
+ .long 0x98d8d9cb, 0x271d9844, 0xb6dd949b
+ .long 0x57a3d037, 0x93a5f730, 0x78d9ccb7
+ .long 0x3771e98f, 0x6b749fb2, 0xbac2fd7b
+ .long 0xe0ac139e, 0xcec3662e, 0xa60ce07b
+ .long 0x6f345e45, 0xe6fc4e6a, 0xce7f39f4
+ .long 0xa2b73df1, 0xb0cd4768, 0x61d82e56
+ .long 0x86d8e4d2, 0xd7a4825c, 0xd270f1a2
+ .long 0xa90fd27a, 0x0167d312, 0xc619809d
+ .long 0xca6ef3ac, 0x26f6a60a, 0x2b3cac5d
+ .long 0x4597456a, 0x98d8d9cb, 0x65863b64
+ .long 0xc9c8b782, 0x68bce87a, 0x1b03397f
+ .long 0x62ec6c6d, 0x6956fc3b, 0xebb883bd
+ .long 0x2342001e, 0x3771e98f, 0xb3e32c28
+ .long 0xe8b6368b, 0x2178513a, 0x064f7f26
+ .long 0x9ef68d35, 0x170076fa, 0xdd7e3b0c
+ .long 0x0b0bf8ca, 0x6f345e45, 0xf285651c
+ .long 0x02ee03b2, 0xff0dba97, 0x10746f3c
+ .long 0x135c83fd, 0xf872e54c, 0xc7a68855
+ .long 0x00bcf5f6, 0x86d8e4d2, 0x271d9844
+ .long 0x58ca5f00, 0x5bb8f1bc, 0x8e766a0c
+ .long 0xded288f8, 0xb3af077a, 0x93a5f730
+ .long 0x37170390, 0xca6ef3ac, 0x6cb08e5c
+ .long 0xf48642e9, 0xdd66cbbb, 0x6b749fb2
+ .long 0xb25b29f2, 0xe9e28eb4, 0x1393e203
+ .long 0x45cddf4e, 0xc9c8b782, 0xcec3662e
+ .long 0xdfd94fb2, 0x93e106a4, 0x96c515bb
+ .long 0x021ac5ef, 0xd813b325, 0xe6fc4e6a
+ .long 0x8e1450f7, 0x2342001e, 0x8227bb8a
+ .long 0xe0cdcf86, 0x6d9a4957, 0xb0cd4768
+ .long 0x613eee91, 0xd2c3ed1a, 0x39c7ff35
+ .long 0xbedc6ba1, 0x9ef68d35, 0xd7a4825c
+ .long 0x0cd1526a, 0xf2271e60, 0x0ab3844b
+ .long 0xd6c3a807, 0x2664fd8b, 0x0167d312
+ .long 0x1d31175f, 0x02ee03b2, 0xf6076544
+ .long 0x4be7fd90, 0x363bd6b3, 0x26f6a60a
+ .long 0x6eeed1c9, 0x5fabe670, 0xa741c1bf
+ .long 0xb3a6da94, 0x00bcf5f6, 0x98d8d9cb
+ .long 0x2e7d11a7, 0x17f27698, 0x49c3cc9c
+ .long 0x889774e1, 0xaa7c7ad5, 0x68bce87a
+ .long 0x8a074012, 0xded288f8, 0x57a3d037
+ .long 0xbd0bb25f, 0x6d390dec, 0x6956fc3b
+ .long 0x3be3c09b, 0x6353c1cc, 0x42d98888
+ .long 0x465a4eee, 0xf48642e9, 0x3771e98f
+ .long 0x2e5f3c8c, 0xdd35bc8d, 0xb42ae3d9
+ .long 0xa52f58ec, 0x9a5ede41, 0x2178513a
+ .long 0x47972100, 0x45cddf4e, 0xe0ac139e
+ .long 0x359674f7, 0xa51b6135, 0x170076fa
+
+.L1: .long 0xaf449247, 0x81256527, 0xccaa009e
+ .long 0x57c54819, 0x1d9513d7, 0x81256527
+ .long 0x3f41287a, 0x57c54819, 0xaf449247
+ .long 0xf5e48c85, 0x910eeec1, 0x1d9513d7
+ .long 0x1f0c2cdd, 0x9026d5b1, 0xae0b5394
+ .long 0x71d54a59, 0xf5e48c85, 0x57c54819
+ .long 0x1c63267b, 0xfe807bbd, 0x0cbec0ed
+ .long 0xd31343ea, 0xe95c1271, 0x910eeec1
+ .long 0xf9d9c7ee, 0x71d54a59, 0x3f41287a
+ .long 0x9ee62949, 0xcec97417, 0x9026d5b1
+ .long 0xa55d1514, 0xf183c71b, 0xd1df2327
+ .long 0x21aa2b26, 0xd31343ea, 0xf5e48c85
+ .long 0x9d842b80, 0xeea395c4, 0x3c656ced
+ .long 0xd8110ff1, 0xcd669a40, 0xfe807bbd
+ .long 0x3f9e9356, 0x9ee62949, 0x1f0c2cdd
+ .long 0x1d6708a0, 0x0c30f51d, 0xe95c1271
+ .long 0xef82aa68, 0xdb3935ea, 0xb918a347
+ .long 0xd14bcc9b, 0x21aa2b26, 0x71d54a59
+ .long 0x99cce860, 0x356d209f, 0xff6f2fc2
+ .long 0xd8af8e46, 0xc352f6de, 0xcec97417
+ .long 0xf1996890, 0xd8110ff1, 0x1c63267b
+ .long 0x631bc508, 0xe95c7216, 0xf183c71b
+ .long 0x8511c306, 0x8e031a19, 0x9b9bdbd0
+ .long 0xdb3839f3, 0x1d6708a0, 0xd31343ea
+ .long 0x7a92fffb, 0xf7003835, 0x4470ac44
+ .long 0x6ce68f2a, 0x00eba0c8, 0xeea395c4
+ .long 0x4caaa263, 0xd14bcc9b, 0xf9d9c7ee
+ .long 0xb46f7cff, 0x9a1b53c8, 0xcd669a40
+ .long 0x60290934, 0x81b6f443, 0x6d40f445
+ .long 0x8e976a7d, 0xd8af8e46, 0x9ee62949
+ .long 0xdcf5088a, 0x9dbdc100, 0x145575d5
+ .long 0x1753ab84, 0xbbf2f6d6, 0x0c30f51d
+ .long 0x255b139e, 0x631bc508, 0xa55d1514
+ .long 0xd784eaa8, 0xce26786c, 0xdb3935ea
+ .long 0x6d2c864a, 0x8068c345, 0x2586d334
+ .long 0x02072e24, 0xdb3839f3, 0x21aa2b26
+ .long 0x06689b0a, 0x5efd72f5, 0xe0575528
+ .long 0x1e52f5ea, 0x4117915b, 0x356d209f
+ .long 0x1d3d1db6, 0x6ce68f2a, 0x9d842b80
+ .long 0x3796455c, 0xb8e0e4a8, 0xc352f6de
+ .long 0xdf3a4eb3, 0xc55a2330, 0xb84ffa9c
+ .long 0x28ae0976, 0xb46f7cff, 0xd8110ff1
+ .long 0x9764bc8d, 0xd7e7a22c, 0x712510f0
+ .long 0x13a13e18, 0x3e9a43cd, 0xe95c7216
+ .long 0xb8ee242e, 0x8e976a7d, 0x3f9e9356
+ .long 0x0c540e7b, 0x753c81ff, 0x8e031a19
+ .long 0x9924c781, 0xb9220208, 0x3edcde65
+ .long 0x3954de39, 0x1753ab84, 0x1d6708a0
+ .long 0xf32238b5, 0xbec81497, 0x9e70b943
+ .long 0xbbd2cd2c, 0x0925d861, 0xf7003835
+ .long 0xcc401304, 0xd784eaa8, 0xef82aa68
+ .long 0x4987e684, 0x6044fbb0, 0x00eba0c8
+ .long 0x3aa11427, 0x18fe3b4a, 0x87441142
+ .long 0x297aad60, 0x02072e24, 0xd14bcc9b
+ .long 0xf60c5e51, 0x6ef6f487, 0x5b7fdd0a
+ .long 0x632d78c5, 0x3fc33de4, 0x9a1b53c8
+ .long 0x25b8822a, 0x1e52f5ea, 0x99cce860
+ .long 0xd4fc84bc, 0x1af62fb8, 0x81b6f443
+ .long 0x5690aa32, 0xa91fdefb, 0x688a110e
+ .long 0x1357a093, 0x3796455c, 0xd8af8e46
+ .long 0x798fdd33, 0xaaa18a37, 0x357b9517
+ .long 0xc2815395, 0x54d42691, 0x9dbdc100
+ .long 0x21cfc0f7, 0x28ae0976, 0xf1996890
+ .long 0xa0decef3, 0x7b4aa8b7, 0xbbf2f6d6
--
2.47.0.rc1.288.g06298d1525-goog

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