xref: /openbmc/linux/arch/mips/include/asm/vdso.h (revision 981ab3f1)
1 /*
2  * Copyright (C) 2015 Imagination Technologies
3  * Author: Alex Smith <alex.smith@imgtec.com>
4  *
5  * This program is free software; you can redistribute it and/or modify it
6  * under the terms of the GNU General Public License as published by the
7  * Free Software Foundation;  either version 2 of the  License, or (at your
8  * option) any later version.
9  */
10 
11 #ifndef __ASM_VDSO_H
12 #define __ASM_VDSO_H
13 
14 #include <linux/mm_types.h>
15 
16 #include <asm/barrier.h>
17 
18 /**
19  * struct mips_vdso_image - Details of a VDSO image.
20  * @data: Pointer to VDSO image data (page-aligned).
21  * @size: Size of the VDSO image data (page-aligned).
22  * @off_sigreturn: Offset of the sigreturn() trampoline.
23  * @off_rt_sigreturn: Offset of the rt_sigreturn() trampoline.
24  * @mapping: Special mapping structure.
25  *
26  * This structure contains details of a VDSO image, including the image data
27  * and offsets of certain symbols required by the kernel. It is generated as
28  * part of the VDSO build process, aside from the mapping page array, which is
29  * populated at runtime.
30  */
31 struct mips_vdso_image {
32 	void *data;
33 	unsigned long size;
34 
35 	unsigned long off_sigreturn;
36 	unsigned long off_rt_sigreturn;
37 
38 	struct vm_special_mapping mapping;
39 };
40 
41 /*
42  * The following structures are auto-generated as part of the build for each
43  * ABI by genvdso, see arch/mips/vdso/Makefile.
44  */
45 
46 extern struct mips_vdso_image vdso_image;
47 
48 #ifdef CONFIG_MIPS32_O32
49 extern struct mips_vdso_image vdso_image_o32;
50 #endif
51 
52 #ifdef CONFIG_MIPS32_N32
53 extern struct mips_vdso_image vdso_image_n32;
54 #endif
55 
56 /**
57  * union mips_vdso_data - Data provided by the kernel for the VDSO.
58  * @xtime_sec:		Current real time (seconds part).
59  * @xtime_nsec:		Current real time (nanoseconds part, shifted).
60  * @wall_to_mono_sec:	Wall-to-monotonic offset (seconds part).
61  * @wall_to_mono_nsec:	Wall-to-monotonic offset (nanoseconds part).
62  * @seq_count:		Counter to synchronise updates (odd = updating).
63  * @cs_shift:		Clocksource shift value.
64  * @clock_mode:		Clocksource to use for time functions.
65  * @cs_mult:		Clocksource multiplier value.
66  * @cs_cycle_last:	Clock cycle value at last update.
67  * @cs_mask:		Clocksource mask value.
68  * @tz_minuteswest:	Minutes west of Greenwich (from timezone).
69  * @tz_dsttime:		Type of DST correction (from timezone).
70  *
71  * This structure contains data needed by functions within the VDSO. It is
72  * populated by the kernel and mapped read-only into user memory. The time
73  * fields are mirrors of internal data from the timekeeping infrastructure.
74  *
75  * Note: Care should be taken when modifying as the layout must remain the same
76  * for both 64- and 32-bit (for 32-bit userland on 64-bit kernel).
77  */
78 union mips_vdso_data {
79 	struct {
80 		u64 xtime_sec;
81 		u64 xtime_nsec;
82 		u64 wall_to_mono_sec;
83 		u64 wall_to_mono_nsec;
84 		u32 seq_count;
85 		u32 cs_shift;
86 		u8 clock_mode;
87 		u32 cs_mult;
88 		u64 cs_cycle_last;
89 		u64 cs_mask;
90 		s32 tz_minuteswest;
91 		s32 tz_dsttime;
92 	};
93 
94 	u8 page[PAGE_SIZE];
95 };
96 
97 static inline u32 vdso_data_read_begin(const union mips_vdso_data *data)
98 {
99 	u32 seq;
100 
101 	while (true) {
102 		seq = ACCESS_ONCE(data->seq_count);
103 		if (likely(!(seq & 1))) {
104 			/* Paired with smp_wmb() in vdso_data_write_*(). */
105 			smp_rmb();
106 			return seq;
107 		}
108 
109 		cpu_relax();
110 	}
111 }
112 
113 static inline bool vdso_data_read_retry(const union mips_vdso_data *data,
114 					u32 start_seq)
115 {
116 	/* Paired with smp_wmb() in vdso_data_write_*(). */
117 	smp_rmb();
118 	return unlikely(data->seq_count != start_seq);
119 }
120 
121 static inline void vdso_data_write_begin(union mips_vdso_data *data)
122 {
123 	++data->seq_count;
124 
125 	/* Ensure sequence update is written before other data page values. */
126 	smp_wmb();
127 }
128 
129 static inline void vdso_data_write_end(union mips_vdso_data *data)
130 {
131 	/* Ensure data values are written before updating sequence again. */
132 	smp_wmb();
133 	++data->seq_count;
134 }
135 
136 #endif /* __ASM_VDSO_H */
137