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 */ 58