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