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 9 static __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 20 static __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 30 static __always_inline void vdso_write_begin(struct vdso_data *vd) 31 { 32 /* 33 * WRITE_ONCE() 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 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 42 static __always_inline void vdso_write_end(struct vdso_data *vd) 43 { 44 smp_wmb(); 45 /* 46 * WRITE_ONCE() 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 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 */ 57