include/vdso/helpers.h

   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
  10 static __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
  21 static __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
  31 static __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
  43 static __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 */