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_clock *vc) 11 { 12 u32 seq; 13 14 while (unlikely((seq = READ_ONCE(vc->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_clock *vc, 22 u32 start) 23 { 24 u32 seq; 25 26 smp_rmb(); 27 seq = READ_ONCE(vc->seq); 28 return seq != start; 29 } 30 31 static __always_inline void vdso_write_begin(struct vdso_time_data *vd) 32 { 33 struct vdso_clock *vc = vd->clock_data; 34 35 /* 36 * WRITE_ONCE() is required otherwise the compiler can validly tear 37 * updates to vd[x].seq and it is possible that the value seen by the 38 * reader is inconsistent. 39 */ 40 WRITE_ONCE(vc[CS_HRES_COARSE].seq, vc[CS_HRES_COARSE].seq + 1); 41 WRITE_ONCE(vc[CS_RAW].seq, vc[CS_RAW].seq + 1); 42 smp_wmb(); 43 } 44 45 static __always_inline void vdso_write_end(struct vdso_time_data *vd) 46 { 47 struct vdso_clock *vc = vd->clock_data; 48 49 smp_wmb(); 50 /* 51 * WRITE_ONCE() is required otherwise the compiler can validly tear 52 * updates to vd[x].seq and it is possible that the value seen by the 53 * reader is inconsistent. 54 */ 55 WRITE_ONCE(vc[CS_HRES_COARSE].seq, vc[CS_HRES_COARSE].seq + 1); 56 WRITE_ONCE(vc[CS_RAW].seq, vc[CS_RAW].seq + 1); 57 } 58 59 #endif /* !__ASSEMBLY__ */ 60 61 #endif /* __VDSO_HELPERS_H */ 62