2 * Copyright 2006 Andi Kleen, SUSE Labs.
3 * Subject to the GNU Public License, v.2
5 * Fast user context implementation of clock_gettime, gettimeofday, and time.
7 * 32 Bit compat layer by Stefani Seibold <stefani@seibold.net>
8 * sponsored by Rohde & Schwarz GmbH & Co. KG Munich/Germany
10 * The code should have no internal unresolved relocations.
11 * Check with readelf after changing.
14 #include <uapi/linux/time.h>
15 #include <asm/vgtod.h>
17 #include <asm/unistd.h>
19 #include <asm/pvclock.h>
20 #include <linux/math64.h>
21 #include <linux/time.h>
22 #include <linux/kernel.h>
24 #define gtod (&VVAR(vsyscall_gtod_data))
26 extern int __vdso_clock_gettime(clockid_t clock
, struct timespec
*ts
);
27 extern int __vdso_gettimeofday(struct timeval
*tv
, struct timezone
*tz
);
28 extern time_t __vdso_time(time_t *t
);
30 #ifdef CONFIG_PARAVIRT_CLOCK
31 extern u8 pvclock_page
32 __attribute__((visibility("hidden")));
37 notrace
static long vdso_fallback_gettime(long clock
, struct timespec
*ts
)
40 asm("syscall" : "=a" (ret
) :
41 "0" (__NR_clock_gettime
), "D" (clock
), "S" (ts
) : "memory");
45 notrace
static long vdso_fallback_gtod(struct timeval
*tv
, struct timezone
*tz
)
49 asm("syscall" : "=a" (ret
) :
50 "0" (__NR_gettimeofday
), "D" (tv
), "S" (tz
) : "memory");
57 notrace
static long vdso_fallback_gettime(long clock
, struct timespec
*ts
)
64 "call __kernel_vsyscall \n"
67 : "0" (__NR_clock_gettime
), "g" (clock
), "c" (ts
)
72 notrace
static long vdso_fallback_gtod(struct timeval
*tv
, struct timezone
*tz
)
79 "call __kernel_vsyscall \n"
82 : "0" (__NR_gettimeofday
), "g" (tv
), "c" (tz
)
89 #ifdef CONFIG_PARAVIRT_CLOCK
90 static notrace
const struct pvclock_vsyscall_time_info
*get_pvti0(void)
92 return (const struct pvclock_vsyscall_time_info
*)&pvclock_page
;
95 static notrace cycle_t
vread_pvclock(int *mode
)
97 const struct pvclock_vcpu_time_info
*pvti
= &get_pvti0()->pvti
;
100 u64 last
, delta
, pvti_system_time
;
101 u32 version
, pvti_tsc_to_system_mul
, pvti_tsc_shift
;
104 * Note: The kernel and hypervisor must guarantee that cpu ID
105 * number maps 1:1 to per-CPU pvclock time info.
107 * Because the hypervisor is entirely unaware of guest userspace
108 * preemption, it cannot guarantee that per-CPU pvclock time
109 * info is updated if the underlying CPU changes or that that
110 * version is increased whenever underlying CPU changes.
112 * On KVM, we are guaranteed that pvti updates for any vCPU are
113 * atomic as seen by *all* vCPUs. This is an even stronger
114 * guarantee than we get with a normal seqlock.
116 * On Xen, we don't appear to have that guarantee, but Xen still
117 * supplies a valid seqlock using the version field.
119 * We only do pvclock vdso timing at all if
120 * PVCLOCK_TSC_STABLE_BIT is set, and we interpret that bit to
121 * mean that all vCPUs have matching pvti and that the TSC is
122 * synced, so we can just look at vCPU 0's pvti.
126 version
= pvti
->version
;
130 if (unlikely(!(pvti
->flags
& PVCLOCK_TSC_STABLE_BIT
))) {
135 tsc
= rdtsc_ordered();
136 pvti_tsc_to_system_mul
= pvti
->tsc_to_system_mul
;
137 pvti_tsc_shift
= pvti
->tsc_shift
;
138 pvti_system_time
= pvti
->system_time
;
139 pvti_tsc
= pvti
->tsc_timestamp
;
141 /* Make sure that the version double-check is last. */
143 } while (unlikely((version
& 1) || version
!= pvti
->version
));
145 delta
= tsc
- pvti_tsc
;
146 ret
= pvti_system_time
+
147 pvclock_scale_delta(delta
, pvti_tsc_to_system_mul
,
150 /* refer to vread_tsc() comment for rationale */
151 last
= gtod
->cycle_last
;
153 if (likely(ret
>= last
))
160 notrace
static cycle_t
vread_tsc(void)
162 cycle_t ret
= (cycle_t
)rdtsc_ordered();
163 u64 last
= gtod
->cycle_last
;
165 if (likely(ret
>= last
))
169 * GCC likes to generate cmov here, but this branch is extremely
170 * predictable (it's just a function of time and the likely is
171 * very likely) and there's a data dependence, so force GCC
172 * to generate a branch instead. I don't barrier() because
173 * we don't actually need a barrier, and if this function
174 * ever gets inlined it will generate worse code.
180 notrace
static inline u64
vgetsns(int *mode
)
185 if (gtod
->vclock_mode
== VCLOCK_TSC
)
186 cycles
= vread_tsc();
187 #ifdef CONFIG_PARAVIRT_CLOCK
188 else if (gtod
->vclock_mode
== VCLOCK_PVCLOCK
)
189 cycles
= vread_pvclock(mode
);
193 v
= (cycles
- gtod
->cycle_last
) & gtod
->mask
;
194 return v
* gtod
->mult
;
197 /* Code size doesn't matter (vdso is 4k anyway) and this is faster. */
198 notrace
static int __always_inline
do_realtime(struct timespec
*ts
)
205 seq
= gtod_read_begin(gtod
);
206 mode
= gtod
->vclock_mode
;
207 ts
->tv_sec
= gtod
->wall_time_sec
;
208 ns
= gtod
->wall_time_snsec
;
209 ns
+= vgetsns(&mode
);
211 } while (unlikely(gtod_read_retry(gtod
, seq
)));
213 ts
->tv_sec
+= __iter_div_u64_rem(ns
, NSEC_PER_SEC
, &ns
);
219 notrace
static int __always_inline
do_monotonic(struct timespec
*ts
)
226 seq
= gtod_read_begin(gtod
);
227 mode
= gtod
->vclock_mode
;
228 ts
->tv_sec
= gtod
->monotonic_time_sec
;
229 ns
= gtod
->monotonic_time_snsec
;
230 ns
+= vgetsns(&mode
);
232 } while (unlikely(gtod_read_retry(gtod
, seq
)));
234 ts
->tv_sec
+= __iter_div_u64_rem(ns
, NSEC_PER_SEC
, &ns
);
240 notrace
static void do_realtime_coarse(struct timespec
*ts
)
244 seq
= gtod_read_begin(gtod
);
245 ts
->tv_sec
= gtod
->wall_time_coarse_sec
;
246 ts
->tv_nsec
= gtod
->wall_time_coarse_nsec
;
247 } while (unlikely(gtod_read_retry(gtod
, seq
)));
250 notrace
static void do_monotonic_coarse(struct timespec
*ts
)
254 seq
= gtod_read_begin(gtod
);
255 ts
->tv_sec
= gtod
->monotonic_time_coarse_sec
;
256 ts
->tv_nsec
= gtod
->monotonic_time_coarse_nsec
;
257 } while (unlikely(gtod_read_retry(gtod
, seq
)));
260 notrace
int __vdso_clock_gettime(clockid_t clock
, struct timespec
*ts
)
264 if (do_realtime(ts
) == VCLOCK_NONE
)
267 case CLOCK_MONOTONIC
:
268 if (do_monotonic(ts
) == VCLOCK_NONE
)
271 case CLOCK_REALTIME_COARSE
:
272 do_realtime_coarse(ts
);
274 case CLOCK_MONOTONIC_COARSE
:
275 do_monotonic_coarse(ts
);
283 return vdso_fallback_gettime(clock
, ts
);
285 int clock_gettime(clockid_t
, struct timespec
*)
286 __attribute__((weak
, alias("__vdso_clock_gettime")));
288 notrace
int __vdso_gettimeofday(struct timeval
*tv
, struct timezone
*tz
)
290 if (likely(tv
!= NULL
)) {
291 if (unlikely(do_realtime((struct timespec
*)tv
) == VCLOCK_NONE
))
292 return vdso_fallback_gtod(tv
, tz
);
295 if (unlikely(tz
!= NULL
)) {
296 tz
->tz_minuteswest
= gtod
->tz_minuteswest
;
297 tz
->tz_dsttime
= gtod
->tz_dsttime
;
302 int gettimeofday(struct timeval
*, struct timezone
*)
303 __attribute__((weak
, alias("__vdso_gettimeofday")));
306 * This will break when the xtime seconds get inaccurate, but that is
309 notrace
time_t __vdso_time(time_t *t
)
311 /* This is atomic on x86 so we don't need any locks. */
312 time_t result
= ACCESS_ONCE(gtod
->wall_time_sec
);
319 __attribute__((weak
, alias("__vdso_time")));