helpers.h (1299B)
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 9static __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 20static __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 30static __always_inline void vdso_write_begin(struct vdso_data *vd) 31{ 32 /* 33 * WRITE_ONCE it 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 it 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 42static __always_inline void vdso_write_end(struct vdso_data *vd) 43{ 44 smp_wmb(); 45 /* 46 * WRITE_ONCE it 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 it 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 */