arch/mips/include/asm/vdso.h

   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                 u32 wall_to_mono_sec;
  83                 u32 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 */