1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
|
// SPDX-License-Identifier: GPL-2.0-only
// Copyright (C) 2019-2020 Arm Ltd.
#include <linux/compiler.h>
#include <linux/kasan-checks.h>
#include <linux/kernel.h>
#include <net/checksum.h>
/* Looks dumb, but generates nice-ish code */
static u64 accumulate(u64 sum, u64 data)
{
__uint128_t tmp = (__uint128_t)sum + data;
return tmp + (tmp >> 64);
}
unsigned int do_csum(const unsigned char *buff, int len)
{
unsigned int offset, shift, sum;
const u64 *ptr;
u64 data, sum64 = 0;
offset = (unsigned long)buff & 7;
/*
* This is to all intents and purposes safe, since rounding down cannot
* result in a different page or cache line being accessed, and @buff
* should absolutely not be pointing to anything read-sensitive. We do,
* however, have to be careful not to piss off KASAN, which means using
* unchecked reads to accommodate the head and tail, for which we'll
* compensate with an explicit check up-front.
*/
kasan_check_read(buff, len);
ptr = (u64 *)(buff - offset);
len = len + offset - 8;
/*
* Head: zero out any excess leading bytes. Shifting back by the same
* amount should be at least as fast as any other way of handling the
* odd/even alignment, and means we can ignore it until the very end.
*/
shift = offset * 8;
data = READ_ONCE_NOCHECK(*ptr++);
#ifdef __LITTLE_ENDIAN
data = (data >> shift) << shift;
#else
data = (data << shift) >> shift;
#endif
/*
* Body: straightforward aligned loads from here on (the paired loads
* underlying the quadword type still only need dword alignment). The
* main loop strictly excludes the tail, so the second loop will always
* run at least once.
*/
while (unlikely(len > 64)) {
__uint128_t tmp1, tmp2, tmp3, tmp4;
tmp1 = READ_ONCE_NOCHECK(*(__uint128_t *)ptr);
tmp2 = READ_ONCE_NOCHECK(*(__uint128_t *)(ptr + 2));
tmp3 = READ_ONCE_NOCHECK(*(__uint128_t *)(ptr + 4));
tmp4 = READ_ONCE_NOCHECK(*(__uint128_t *)(ptr + 6));
len -= 64;
ptr += 8;
/* This is the "don't dump the carry flag into a GPR" idiom */
tmp1 += (tmp1 >> 64) | (tmp1 << 64);
tmp2 += (tmp2 >> 64) | (tmp2 << 64);
tmp3 += (tmp3 >> 64) | (tmp3 << 64);
tmp4 += (tmp4 >> 64) | (tmp4 << 64);
tmp1 = ((tmp1 >> 64) << 64) | (tmp2 >> 64);
tmp1 += (tmp1 >> 64) | (tmp1 << 64);
tmp3 = ((tmp3 >> 64) << 64) | (tmp4 >> 64);
tmp3 += (tmp3 >> 64) | (tmp3 << 64);
tmp1 = ((tmp1 >> 64) << 64) | (tmp3 >> 64);
tmp1 += (tmp1 >> 64) | (tmp1 << 64);
tmp1 = ((tmp1 >> 64) << 64) | sum64;
tmp1 += (tmp1 >> 64) | (tmp1 << 64);
sum64 = tmp1 >> 64;
}
while (len > 8) {
__uint128_t tmp;
sum64 = accumulate(sum64, data);
tmp = READ_ONCE_NOCHECK(*(__uint128_t *)ptr);
len -= 16;
ptr += 2;
#ifdef __LITTLE_ENDIAN
data = tmp >> 64;
sum64 = accumulate(sum64, tmp);
#else
data = tmp;
sum64 = accumulate(sum64, tmp >> 64);
#endif
}
if (len > 0) {
sum64 = accumulate(sum64, data);
data = READ_ONCE_NOCHECK(*ptr);
len -= 8;
}
/*
* Tail: zero any over-read bytes similarly to the head, again
* preserving odd/even alignment.
*/
shift = len * -8;
#ifdef __LITTLE_ENDIAN
data = (data << shift) >> shift;
#else
data = (data >> shift) << shift;
#endif
sum64 = accumulate(sum64, data);
/* Finally, folding */
sum64 += (sum64 >> 32) | (sum64 << 32);
sum = sum64 >> 32;
sum += (sum >> 16) | (sum << 16);
if (offset & 1)
return (u16)swab32(sum);
return sum >> 16;
}
|
