1/*
  2 * Copyright 2006 Andi Kleen, SUSE Labs.
  3 * Subject to the GNU Public License, v.2
  4 *
  5 * Fast user context implementation of clock_gettime, gettimeofday, and time.
  6 *
  7 * The code should have no internal unresolved relocations.
  8 * Check with readelf after changing.
  9 */
 10
 11/* Disable profiling for userspace code: */
 12#define DISABLE_BRANCH_PROFILING
 13
 14#include <linux/kernel.h>
 15#include <linux/posix-timers.h>
 16#include <linux/time.h>
 17#include <linux/string.h>
 18#include <asm/vsyscall.h>
 19#include <asm/fixmap.h>
 20#include <asm/vgtod.h>
 21#include <asm/timex.h>
 22#include <asm/hpet.h>
 23#include <asm/unistd.h>
 24#include <asm/io.h>
 25
 26#define gtod (&VVAR(vsyscall_gtod_data))
 27
 28notrace static cycle_t vread_tsc(void)
 29{
 30	cycle_t ret;
 31	u64 last;
 32
 33	/*
 34	 * Empirically, a fence (of type that depends on the CPU)
 35	 * before rdtsc is enough to ensure that rdtsc is ordered
 36	 * with respect to loads.  The various CPU manuals are unclear
 37	 * as to whether rdtsc can be reordered with later loads,
 38	 * but no one has ever seen it happen.
 39	 */
 40	rdtsc_barrier();
 41	ret = (cycle_t)vget_cycles();
 42
 43	last = VVAR(vsyscall_gtod_data).clock.cycle_last;
 44
 45	if (likely(ret >= last))
 46		return ret;
 47
 48	/*
 49	 * GCC likes to generate cmov here, but this branch is extremely
 50	 * predictable (it's just a funciton of time and the likely is
 51	 * very likely) and there's a data dependence, so force GCC
 52	 * to generate a branch instead.  I don't barrier() because
 53	 * we don't actually need a barrier, and if this function
 54	 * ever gets inlined it will generate worse code.
 55	 */
 56	asm volatile ("");
 57	return last;
 58}
 59
 60static notrace cycle_t vread_hpet(void)
 61{
 62	return readl((const void __iomem *)fix_to_virt(VSYSCALL_HPET) + 0xf0);
 63}
 64
 65notrace static long vdso_fallback_gettime(long clock, struct timespec *ts)
 66{
 67	long ret;
 68	asm("syscall" : "=a" (ret) :
 69	    "0" (__NR_clock_gettime),"D" (clock), "S" (ts) : "memory");
 70	return ret;
 71}
 72
 73notrace static inline long vgetns(void)
 74{
 75	long v;
 76	cycles_t cycles;
 77	if (gtod->clock.vclock_mode == VCLOCK_TSC)
 78		cycles = vread_tsc();
 79	else
 80		cycles = vread_hpet();
 81	v = (cycles - gtod->clock.cycle_last) & gtod->clock.mask;
 82	return (v * gtod->clock.mult) >> gtod->clock.shift;
 83}
 84
 85notrace static noinline int do_realtime(struct timespec *ts)
 86{
 87	unsigned long seq, ns;
 88	do {
 89		seq = read_seqbegin(&gtod->lock);
 90		ts->tv_sec = gtod->wall_time_sec;
 91		ts->tv_nsec = gtod->wall_time_nsec;
 92		ns = vgetns();
 93	} while (unlikely(read_seqretry(&gtod->lock, seq)));
 94	timespec_add_ns(ts, ns);
 95	return 0;
 96}
 97
 98notrace static noinline int do_monotonic(struct timespec *ts)
 99{
100	unsigned long seq, ns, secs;
101	do {
102		seq = read_seqbegin(&gtod->lock);
103		secs = gtod->wall_time_sec;
104		ns = gtod->wall_time_nsec + vgetns();
105		secs += gtod->wall_to_monotonic.tv_sec;
106		ns += gtod->wall_to_monotonic.tv_nsec;
107	} while (unlikely(read_seqretry(&gtod->lock, seq)));
108
109	/* wall_time_nsec, vgetns(), and wall_to_monotonic.tv_nsec
110	 * are all guaranteed to be nonnegative.
111	 */
112	while (ns >= NSEC_PER_SEC) {
113		ns -= NSEC_PER_SEC;
114		++secs;
115	}
116	ts->tv_sec = secs;
117	ts->tv_nsec = ns;
118
119	return 0;
120}
121
122notrace static noinline int do_realtime_coarse(struct timespec *ts)
123{
124	unsigned long seq;
125	do {
126		seq = read_seqbegin(&gtod->lock);
127		ts->tv_sec = gtod->wall_time_coarse.tv_sec;
128		ts->tv_nsec = gtod->wall_time_coarse.tv_nsec;
129	} while (unlikely(read_seqretry(&gtod->lock, seq)));
130	return 0;
131}
132
133notrace static noinline int do_monotonic_coarse(struct timespec *ts)
134{
135	unsigned long seq, ns, secs;
136	do {
137		seq = read_seqbegin(&gtod->lock);
138		secs = gtod->wall_time_coarse.tv_sec;
139		ns = gtod->wall_time_coarse.tv_nsec;
140		secs += gtod->wall_to_monotonic.tv_sec;
141		ns += gtod->wall_to_monotonic.tv_nsec;
142	} while (unlikely(read_seqretry(&gtod->lock, seq)));
143
144	/* wall_time_nsec and wall_to_monotonic.tv_nsec are
145	 * guaranteed to be between 0 and NSEC_PER_SEC.
146	 */
147	if (ns >= NSEC_PER_SEC) {
148		ns -= NSEC_PER_SEC;
149		++secs;
150	}
151	ts->tv_sec = secs;
152	ts->tv_nsec = ns;
153
154	return 0;
155}
156
157notrace int __vdso_clock_gettime(clockid_t clock, struct timespec *ts)
158{
159	switch (clock) {
160	case CLOCK_REALTIME:
161		if (likely(gtod->clock.vclock_mode != VCLOCK_NONE))
162			return do_realtime(ts);
163		break;
164	case CLOCK_MONOTONIC:
165		if (likely(gtod->clock.vclock_mode != VCLOCK_NONE))
166			return do_monotonic(ts);
167		break;
168	case CLOCK_REALTIME_COARSE:
169		return do_realtime_coarse(ts);
170	case CLOCK_MONOTONIC_COARSE:
171		return do_monotonic_coarse(ts);
172	}
173
174	return vdso_fallback_gettime(clock, ts);
175}
176int clock_gettime(clockid_t, struct timespec *)
177	__attribute__((weak, alias("__vdso_clock_gettime")));
178
179notrace int __vdso_gettimeofday(struct timeval *tv, struct timezone *tz)
180{
181	long ret;
182	if (likely(gtod->clock.vclock_mode != VCLOCK_NONE)) {
183		if (likely(tv != NULL)) {
184			BUILD_BUG_ON(offsetof(struct timeval, tv_usec) !=
185				     offsetof(struct timespec, tv_nsec) ||
186				     sizeof(*tv) != sizeof(struct timespec));
187			do_realtime((struct timespec *)tv);
188			tv->tv_usec /= 1000;
189		}
190		if (unlikely(tz != NULL)) {
191			/* Avoid memcpy. Some old compilers fail to inline it */
192			tz->tz_minuteswest = gtod->sys_tz.tz_minuteswest;
193			tz->tz_dsttime = gtod->sys_tz.tz_dsttime;
194		}
195		return 0;
196	}
197	asm("syscall" : "=a" (ret) :
198	    "0" (__NR_gettimeofday), "D" (tv), "S" (tz) : "memory");
199	return ret;
200}
201int gettimeofday(struct timeval *, struct timezone *)
202	__attribute__((weak, alias("__vdso_gettimeofday")));
203
204/*
205 * This will break when the xtime seconds get inaccurate, but that is
206 * unlikely
207 */
208notrace time_t __vdso_time(time_t *t)
209{
210	/* This is atomic on x86_64 so we don't need any locks. */
211	time_t result = ACCESS_ONCE(VVAR(vsyscall_gtod_data).wall_time_sec);
212
213	if (t)
214		*t = result;
215	return result;
216}
217int time(time_t *t)
218	__attribute__((weak, alias("__vdso_time")));