1 /* SPDX-License-Identifier: GPL-2.0 */
2 #ifndef __VDSO_HELPERS_H
3 #define __VDSO_HELPERS_H
4
5 #ifndef __ASSEMBLY__
6
7 #include <vdso/datapage.h>
8
9 static __always_inline u32 vdso_read_begin(const struct vdso_data *vd)
10 {
11 u32 seq;
12
13 while (unlikely((seq = READ_ONCE(vd->seq)) & 1))
14 cpu_relax();
15
16 smp_rmb();
17 return seq;
18 }
19
20 static __always_inline u32 vdso_read_retry(const struct vdso_data *vd,
21 u32 start)
22 {
23 u32 seq;
24
25 smp_rmb();
26 seq = READ_ONCE(vd->seq);
27 return seq != start;
28 }
29
30 static __always_inline void vdso_write_begin(struct vdso_data *vd)
31 {
32 /*
33 * WRITE_ONCE() is required otherwise the compiler can validly tear
34 * updates to vd[x].seq and it is possible that the value seen by the
35 * reader is inconsistent.
36 */
37 WRITE_ONCE(vd[CS_HRES_COARSE].seq, vd[CS_HRES_COARSE].seq + 1);
38 WRITE_ONCE(vd[CS_RAW].seq, vd[CS_RAW].seq + 1);
39 smp_wmb();
40 }
41
42 static __always_inline void vdso_write_end(struct vdso_data *vd)
43 {
44 smp_wmb();
45 /*
46 * WRITE_ONCE() is required otherwise the compiler can validly tear
47 * updates to vd[x].seq and it is possible that the value seen by the
48 * reader is inconsistent.
49 */
50 WRITE_ONCE(vd[CS_HRES_COARSE].seq, vd[CS_HRES_COARSE].seq + 1);
51 WRITE_ONCE(vd[CS_RAW].seq, vd[CS_RAW].seq + 1);
52 }
53
54 #endif /* !__ASSEMBLY__ */
55
56 #endif /* __VDSO_HELPERS_H */
57
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