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 <asm/mshyperv.h>
21 #include <linux/math64.h>
22 #include <linux/time.h>
23 #include <linux/kernel.h>
25 #define gtod (&VVAR(vsyscall_gtod_data))
27 extern int __vdso_clock_gettime(clockid_t clock, struct timespec *ts);
28 extern int __vdso_gettimeofday(struct timeval *tv, struct timezone *tz);
29 extern time_t __vdso_time(time_t *t);
31 #ifdef CONFIG_PARAVIRT_CLOCK
32 extern u8 pvclock_page[PAGE_SIZE]
33 __attribute__((visibility("hidden")));
36 #ifdef CONFIG_HYPERV_TSCPAGE
37 extern u8 hvclock_page[PAGE_SIZE]
38 __attribute__((visibility("hidden")));
43 notrace static long vdso_fallback_gettime(long clock, struct timespec *ts)
46 asm ("syscall" : "=a" (ret), "=m" (*ts) :
47 "0" (__NR_clock_gettime), "D" (clock), "S" (ts) :
48 "memory", "rcx", "r11");
52 notrace static long vdso_fallback_gtod(struct timeval *tv, struct timezone *tz)
56 asm ("syscall" : "=a" (ret), "=m" (*tv), "=m" (*tz) :
57 "0" (__NR_gettimeofday), "D" (tv), "S" (tz) :
58 "memory", "rcx", "r11");
65 notrace static long vdso_fallback_gettime(long clock, struct timespec *ts)
71 "mov %[clock], %%ebx \n"
72 "call __kernel_vsyscall \n"
74 : "=a" (ret), "=m" (*ts)
75 : "0" (__NR_clock_gettime), [clock] "g" (clock), "c" (ts)
80 notrace static long vdso_fallback_gtod(struct timeval *tv, struct timezone *tz)
87 "call __kernel_vsyscall \n"
89 : "=a" (ret), "=m" (*tv), "=m" (*tz)
90 : "0" (__NR_gettimeofday), [tv] "g" (tv), "c" (tz)
97 #ifdef CONFIG_PARAVIRT_CLOCK
98 static notrace const struct pvclock_vsyscall_time_info *get_pvti0(void)
100 return (const struct pvclock_vsyscall_time_info *)&pvclock_page;
103 static notrace u64 vread_pvclock(int *mode)
105 const struct pvclock_vcpu_time_info *pvti = &get_pvti0()->pvti;
111 * Note: The kernel and hypervisor must guarantee that cpu ID
112 * number maps 1:1 to per-CPU pvclock time info.
114 * Because the hypervisor is entirely unaware of guest userspace
115 * preemption, it cannot guarantee that per-CPU pvclock time
116 * info is updated if the underlying CPU changes or that that
117 * version is increased whenever underlying CPU changes.
119 * On KVM, we are guaranteed that pvti updates for any vCPU are
120 * atomic as seen by *all* vCPUs. This is an even stronger
121 * guarantee than we get with a normal seqlock.
123 * On Xen, we don't appear to have that guarantee, but Xen still
124 * supplies a valid seqlock using the version field.
126 * We only do pvclock vdso timing at all if
127 * PVCLOCK_TSC_STABLE_BIT is set, and we interpret that bit to
128 * mean that all vCPUs have matching pvti and that the TSC is
129 * synced, so we can just look at vCPU 0's pvti.
133 version = pvclock_read_begin(pvti);
135 if (unlikely(!(pvti->flags & PVCLOCK_TSC_STABLE_BIT))) {
140 ret = __pvclock_read_cycles(pvti, rdtsc_ordered());
141 } while (pvclock_read_retry(pvti, version));
143 /* refer to vread_tsc() comment for rationale */
144 last = gtod->cycle_last;
146 if (likely(ret >= last))
152 #ifdef CONFIG_HYPERV_TSCPAGE
153 static notrace u64 vread_hvclock(int *mode)
155 const struct ms_hyperv_tsc_page *tsc_pg =
156 (const struct ms_hyperv_tsc_page *)&hvclock_page;
157 u64 current_tick = hv_read_tsc_page(tsc_pg);
159 if (current_tick != U64_MAX)
167 notrace static u64 vread_tsc(void)
169 u64 ret = (u64)rdtsc_ordered();
170 u64 last = gtod->cycle_last;
172 if (likely(ret >= last))
176 * GCC likes to generate cmov here, but this branch is extremely
177 * predictable (it's just a function of time and the likely is
178 * very likely) and there's a data dependence, so force GCC
179 * to generate a branch instead. I don't barrier() because
180 * we don't actually need a barrier, and if this function
181 * ever gets inlined it will generate worse code.
187 notrace static inline u64 vgetsns(int *mode)
192 if (gtod->vclock_mode == VCLOCK_TSC)
193 cycles = vread_tsc();
196 * For any memory-mapped vclock type, we need to make sure that gcc
197 * doesn't cleverly hoist a load before the mode check. Otherwise we
198 * might end up touching the memory-mapped page even if the vclock in
199 * question isn't enabled, which will segfault. Hence the barriers.
201 #ifdef CONFIG_PARAVIRT_CLOCK
202 else if (gtod->vclock_mode == VCLOCK_PVCLOCK) {
204 cycles = vread_pvclock(mode);
207 #ifdef CONFIG_HYPERV_TSCPAGE
208 else if (gtod->vclock_mode == VCLOCK_HVCLOCK) {
210 cycles = vread_hvclock(mode);
215 v = (cycles - gtod->cycle_last) & gtod->mask;
216 return v * gtod->mult;
219 /* Code size doesn't matter (vdso is 4k anyway) and this is faster. */
220 notrace static int __always_inline do_realtime(struct timespec *ts)
227 seq = gtod_read_begin(gtod);
228 mode = gtod->vclock_mode;
229 ts->tv_sec = gtod->wall_time_sec;
230 ns = gtod->wall_time_snsec;
231 ns += vgetsns(&mode);
233 } while (unlikely(gtod_read_retry(gtod, seq)));
235 ts->tv_sec += __iter_div_u64_rem(ns, NSEC_PER_SEC, &ns);
241 notrace static int __always_inline do_monotonic(struct timespec *ts)
248 seq = gtod_read_begin(gtod);
249 mode = gtod->vclock_mode;
250 ts->tv_sec = gtod->monotonic_time_sec;
251 ns = gtod->monotonic_time_snsec;
252 ns += vgetsns(&mode);
254 } while (unlikely(gtod_read_retry(gtod, seq)));
256 ts->tv_sec += __iter_div_u64_rem(ns, NSEC_PER_SEC, &ns);
262 notrace static void do_realtime_coarse(struct timespec *ts)
266 seq = gtod_read_begin(gtod);
267 ts->tv_sec = gtod->wall_time_coarse_sec;
268 ts->tv_nsec = gtod->wall_time_coarse_nsec;
269 } while (unlikely(gtod_read_retry(gtod, seq)));
272 notrace static void do_monotonic_coarse(struct timespec *ts)
276 seq = gtod_read_begin(gtod);
277 ts->tv_sec = gtod->monotonic_time_coarse_sec;
278 ts->tv_nsec = gtod->monotonic_time_coarse_nsec;
279 } while (unlikely(gtod_read_retry(gtod, seq)));
282 notrace int __vdso_clock_gettime(clockid_t clock, struct timespec *ts)
286 if (do_realtime(ts) == VCLOCK_NONE)
289 case CLOCK_MONOTONIC:
290 if (do_monotonic(ts) == VCLOCK_NONE)
293 case CLOCK_REALTIME_COARSE:
294 do_realtime_coarse(ts);
296 case CLOCK_MONOTONIC_COARSE:
297 do_monotonic_coarse(ts);
305 return vdso_fallback_gettime(clock, ts);
307 int clock_gettime(clockid_t, struct timespec *)
308 __attribute__((weak, alias("__vdso_clock_gettime")));
310 notrace int __vdso_gettimeofday(struct timeval *tv, struct timezone *tz)
312 if (likely(tv != NULL)) {
313 if (unlikely(do_realtime((struct timespec *)tv) == VCLOCK_NONE))
314 return vdso_fallback_gtod(tv, tz);
317 if (unlikely(tz != NULL)) {
318 tz->tz_minuteswest = gtod->tz_minuteswest;
319 tz->tz_dsttime = gtod->tz_dsttime;
324 int gettimeofday(struct timeval *, struct timezone *)
325 __attribute__((weak, alias("__vdso_gettimeofday")));
328 * This will break when the xtime seconds get inaccurate, but that is
331 notrace time_t __vdso_time(time_t *t)
333 /* This is atomic on x86 so we don't need any locks. */
334 time_t result = ACCESS_ONCE(gtod->wall_time_sec);
341 __attribute__((weak, alias("__vdso_time")));