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1// SPDX-License-Identifier: GPL-2.0
2
3#include <vmlinux.h>
4#include <bpf/bpf_core_read.h>
5#include <bpf/bpf_helpers.h>
6#include <bpf/bpf_tracing.h>
7#include "bpf_misc.h"
8
9char _license[] SEC("license") = "GPL";
10
11/* typically virtio scsi has max SGs of 6 */
12#define VIRTIO_MAX_SGS 6
13
14/* Verifier will fail with SG_MAX = 128. The failure can be
15 * workarounded with a smaller SG_MAX, e.g. 10.
16 */
17#define WORKAROUND
18#ifdef WORKAROUND
19#define SG_MAX 10
20#else
21/* typically virtio blk has max SEG of 128 */
22#define SG_MAX 128
23#endif
24
25#define SG_CHAIN 0x01UL
26#define SG_END 0x02UL
27
28#define sg_is_chain(sg) ((sg)->page_link & SG_CHAIN)
29#define sg_is_last(sg) ((sg)->page_link & SG_END)
30#define sg_chain_ptr(sg) \
31 ((struct scatterlist *) ((sg)->page_link & ~(SG_CHAIN | SG_END)))
32
33static inline struct scatterlist *__sg_next(struct scatterlist *sgp)
34{
35 struct scatterlist sg;
36
37 bpf_probe_read_kernel(&sg, sizeof(sg), sgp);
38 if (sg_is_last(&sg))
39 return NULL;
40
41 sgp++;
42
43 bpf_probe_read_kernel(&sg, sizeof(sg), sgp);
44 if (sg_is_chain(&sg))
45 sgp = sg_chain_ptr(&sg);
46
47 return sgp;
48}
49
50static inline struct scatterlist *get_sgp(struct scatterlist **sgs, int i)
51{
52 struct scatterlist *sgp;
53
54 bpf_probe_read_kernel(&sgp, sizeof(sgp), sgs + i);
55 return sgp;
56}
57
58int run_once = 0;
59int result = 0;
60
61SEC("kprobe/virtqueue_add_sgs")
62int BPF_KPROBE(trace_virtqueue_add_sgs, void *unused, struct scatterlist **sgs,
63 unsigned int out_sgs, unsigned int in_sgs)
64{
65 struct scatterlist *sgp = NULL;
66 __u64 length1 = 0, length2 = 0;
67 unsigned int i, n, len;
68
69 if (run_once != 0)
70 return 0;
71
72 for (i = 0; (i < VIRTIO_MAX_SGS) && (i < out_sgs); i++) {
73 __sink(out_sgs);
74 for (n = 0, sgp = get_sgp(sgs, i); sgp && (n < SG_MAX);
75 sgp = __sg_next(sgp)) {
76 len = BPF_CORE_READ(sgp, length);
77 length1 += len;
78 n++;
79 }
80 }
81
82 for (i = 0; (i < VIRTIO_MAX_SGS) && (i < in_sgs); i++) {
83 __sink(in_sgs);
84 for (n = 0, sgp = get_sgp(sgs, i); sgp && (n < SG_MAX);
85 sgp = __sg_next(sgp)) {
86 len = BPF_CORE_READ(sgp, length);
87 length2 += len;
88 n++;
89 }
90 }
91
92 run_once = 1;
93 result = length2 - length1;
94 return 0;
95}