arch/x86/vdso/vclock_gettime.c - maze/linux - Git at Google

 /*
  * Copyright 2006 Andi Kleen, SUSE Labs.
  * Subject to the GNU Public License, v.2
  *
  * Fast user context implementation of clock_gettime, gettimeofday, and time.
  *
  * The code should have no internal unresolved relocations.
  * Check with readelf after changing.
  */

 /* Disable profiling for userspace code: */
 #define DISABLE_BRANCH_PROFILING

 #include <linux/kernel.h>
 #include <linux/posix-timers.h>
 #include <linux/time.h>
 #include <linux/string.h>
 #include <asm/vsyscall.h>
 #include <asm/fixmap.h>
 #include <asm/vgtod.h>
 #include <asm/timex.h>
 #include <asm/hpet.h>
 #include <asm/unistd.h>
 #include <asm/io.h>
 #include <asm/pvclock.h>

 #define gtod (&VVAR(vsyscall_gtod_data))

 notrace static cycle_t vread_tsc(void)
 {
 	cycle_t ret;
 	u64 last;

 	/*
 	 * Empirically, a fence (of type that depends on the CPU)
 	 * before rdtsc is enough to ensure that rdtsc is ordered
 	 * with respect to loads.  The various CPU manuals are unclear
 	 * as to whether rdtsc can be reordered with later loads,
 	 * but no one has ever seen it happen.
 	 */
 	rdtsc_barrier();
 	ret = (cycle_t)vget_cycles();

 	last = VVAR(vsyscall_gtod_data).clock.cycle_last;

 	if (likely(ret >= last))
 		return ret;

 	/*
 	 * GCC likes to generate cmov here, but this branch is extremely
 	 * predictable (it's just a funciton of time and the likely is
 	 * very likely) and there's a data dependence, so force GCC
 	 * to generate a branch instead.  I don't barrier() because
 	 * we don't actually need a barrier, and if this function
 	 * ever gets inlined it will generate worse code.
 	 */
 	asm volatile ("");
 	return last;
 }

 static notrace cycle_t vread_hpet(void)
 {
 	return readl((const void __iomem *)fix_to_virt(VSYSCALL_HPET) + HPET_COUNTER);
 }

 #ifdef CONFIG_PARAVIRT_CLOCK

 static notrace const struct pvclock_vsyscall_time_info *get_pvti(int cpu)
 {
 	const struct pvclock_vsyscall_time_info *pvti_base;
 	int idx = cpu / (PAGE_SIZE/PVTI_SIZE);
 	int offset = cpu % (PAGE_SIZE/PVTI_SIZE);

 	BUG_ON(PVCLOCK_FIXMAP_BEGIN + idx > PVCLOCK_FIXMAP_END);

 	pvti_base = (struct pvclock_vsyscall_time_info *)
 		    __fix_to_virt(PVCLOCK_FIXMAP_BEGIN+idx);

 	return &pvti_base[offset];
 }

 static notrace cycle_t vread_pvclock(int *mode)
 {
 	const struct pvclock_vsyscall_time_info *pvti;
 	cycle_t ret;
 	u64 last;
 	u32 version;
 	u32 migrate_count;
 	u8 flags;
 	unsigned cpu, cpu1;


 	/*
 	 * When looping to get a consistent (time-info, tsc) pair, we
 	 * also need to deal with the possibility we can switch vcpus,
 	 * so make sure we always re-fetch time-info for the current vcpu.
 	 */
 	do {
 		cpu = __getcpu() & VGETCPU_CPU_MASK;
 		/* TODO: We can put vcpu id into higher bits of pvti.version.
 		 * This will save a couple of cycles by getting rid of
 		 * __getcpu() calls (Gleb).
 		 */

 		pvti = get_pvti(cpu);

 		migrate_count = pvti->migrate_count;

 		version = __pvclock_read_cycles(&pvti->pvti, &ret, &flags);

 		/*
 		 * Test we're still on the cpu as well as the version.
 		 * We could have been migrated just after the first
 		 * vgetcpu but before fetching the version, so we
 		 * wouldn't notice a version change.
 		 */
 		cpu1 = __getcpu() & VGETCPU_CPU_MASK;
 	} while (unlikely(cpu != cpu1 ||
 			  (pvti->pvti.version & 1) ||
 			  pvti->pvti.version != version ||
 			  pvti->migrate_count != migrate_count));

 	if (unlikely(!(flags & PVCLOCK_TSC_STABLE_BIT)))
 		*mode = VCLOCK_NONE;

 	/* refer to tsc.c read_tsc() comment for rationale */
 	last = VVAR(vsyscall_gtod_data).clock.cycle_last;

 	if (likely(ret >= last))
 		return ret;

 	return last;
 }
 #endif

 notrace static long vdso_fallback_gettime(long clock, struct timespec *ts)
 {
 	long ret;
 	asm("syscall" : "=a" (ret) :
 	    "0" (__NR_clock_gettime),"D" (clock), "S" (ts) : "memory");
 	return ret;
 }

 notrace static long vdso_fallback_gtod(struct timeval *tv, struct timezone *tz)
 {
 	long ret;

 	asm("syscall" : "=a" (ret) :
 	    "0" (__NR_gettimeofday), "D" (tv), "S" (tz) : "memory");
 	return ret;
 }


 notrace static inline u64 vgetsns(int *mode)
 {
 	long v;
 	cycles_t cycles;
 	if (gtod->clock.vclock_mode == VCLOCK_TSC)
 		cycles = vread_tsc();
 	else if (gtod->clock.vclock_mode == VCLOCK_HPET)
 		cycles = vread_hpet();
 #ifdef CONFIG_PARAVIRT_CLOCK
 	else if (gtod->clock.vclock_mode == VCLOCK_PVCLOCK)
 		cycles = vread_pvclock(mode);
 #endif
 	else
 		return 0;
 	v = (cycles - gtod->clock.cycle_last) & gtod->clock.mask;
 	return v * gtod->clock.mult;
 }

 /* Code size doesn't matter (vdso is 4k anyway) and this is faster. */
 notrace static int __always_inline do_realtime(struct timespec *ts)
 {
 	unsigned long seq;
 	u64 ns;
 	int mode;

 	ts->tv_nsec = 0;
 	do {
 		seq = read_seqcount_begin(&gtod->seq);
 		mode = gtod->clock.vclock_mode;
 		ts->tv_sec = gtod->wall_time_sec;
 		ns = gtod->wall_time_snsec;
 		ns += vgetsns(&mode);
 		ns >>= gtod->clock.shift;
 	} while (unlikely(read_seqcount_retry(&gtod->seq, seq)));

 	timespec_add_ns(ts, ns);
 	return mode;
 }

 notrace static int do_monotonic(struct timespec *ts)
 {
 	unsigned long seq;
 	u64 ns;
 	int mode;

 	ts->tv_nsec = 0;
 	do {
 		seq = read_seqcount_begin(&gtod->seq);
 		mode = gtod->clock.vclock_mode;
 		ts->tv_sec = gtod->monotonic_time_sec;
 		ns = gtod->monotonic_time_snsec;
 		ns += vgetsns(&mode);
 		ns >>= gtod->clock.shift;
 	} while (unlikely(read_seqcount_retry(&gtod->seq, seq)));
 	timespec_add_ns(ts, ns);

 	return mode;
 }

 notrace static int do_realtime_coarse(struct timespec *ts)
 {
 	unsigned long seq;
 	do {
 		seq = read_seqcount_begin(&gtod->seq);
 		ts->tv_sec = gtod->wall_time_coarse.tv_sec;
 		ts->tv_nsec = gtod->wall_time_coarse.tv_nsec;
 	} while (unlikely(read_seqcount_retry(&gtod->seq, seq)));
 	return 0;
 }

 notrace static int do_monotonic_coarse(struct timespec *ts)
 {
 	unsigned long seq;
 	do {
 		seq = read_seqcount_begin(&gtod->seq);
 		ts->tv_sec = gtod->monotonic_time_coarse.tv_sec;
 		ts->tv_nsec = gtod->monotonic_time_coarse.tv_nsec;
 	} while (unlikely(read_seqcount_retry(&gtod->seq, seq)));

 	return 0;
 }

 notrace int __vdso_clock_gettime(clockid_t clock, struct timespec *ts)
 {
 	int ret = VCLOCK_NONE;

 	switch (clock) {
 	case CLOCK_REALTIME:
 		ret = do_realtime(ts);
 		break;
 	case CLOCK_MONOTONIC:
 		ret = do_monotonic(ts);
 		break;
 	case CLOCK_REALTIME_COARSE:
 		return do_realtime_coarse(ts);
 	case CLOCK_MONOTONIC_COARSE:
 		return do_monotonic_coarse(ts);
 	}

 	if (ret == VCLOCK_NONE)
 		return vdso_fallback_gettime(clock, ts);
 	return 0;
 }
 int clock_gettime(clockid_t, struct timespec *)
 	__attribute__((weak, alias("__vdso_clock_gettime")));

 notrace int __vdso_gettimeofday(struct timeval *tv, struct timezone *tz)
 {
 	long ret = VCLOCK_NONE;

 	if (likely(tv != NULL)) {
 		BUILD_BUG_ON(offsetof(struct timeval, tv_usec) !=
 			     offsetof(struct timespec, tv_nsec) ||
 			     sizeof(*tv) != sizeof(struct timespec));
 		ret = do_realtime((struct timespec *)tv);
 		tv->tv_usec /= 1000;
 	}
 	if (unlikely(tz != NULL)) {
 		/* Avoid memcpy. Some old compilers fail to inline it */
 		tz->tz_minuteswest = gtod->sys_tz.tz_minuteswest;
 		tz->tz_dsttime = gtod->sys_tz.tz_dsttime;
 	}

 	if (ret == VCLOCK_NONE)
 		return vdso_fallback_gtod(tv, tz);
 	return 0;
 }
 int gettimeofday(struct timeval *, struct timezone *)
 	__attribute__((weak, alias("__vdso_gettimeofday")));

 /*
  * This will break when the xtime seconds get inaccurate, but that is
  * unlikely
  */
 notrace time_t __vdso_time(time_t *t)
 {
 	/* This is atomic on x86_64 so we don't need any locks. */
 	time_t result = ACCESS_ONCE(VVAR(vsyscall_gtod_data).wall_time_sec);

 	if (t)
 		*t = result;
 	return result;
 }
 int time(time_t *t)
 	__attribute__((weak, alias("__vdso_time")));
	/*
	* Copyright 2006 Andi Kleen, SUSE Labs.
	* Subject to the GNU Public License, v.2
	*
	* Fast user context implementation of clock_gettime, gettimeofday, and time.
	*
	* The code should have no internal unresolved relocations.
	* Check with readelf after changing.
	*/

	/* Disable profiling for userspace code: */
	#define DISABLE_BRANCH_PROFILING

	#include <linux/kernel.h>
	#include <linux/posix-timers.h>
	#include <linux/time.h>
	#include <linux/string.h>
	#include <asm/vsyscall.h>
	#include <asm/fixmap.h>
	#include <asm/vgtod.h>
	#include <asm/timex.h>
	#include <asm/hpet.h>
	#include <asm/unistd.h>
	#include <asm/io.h>
	#include <asm/pvclock.h>

	#define gtod (&VVAR(vsyscall_gtod_data))

	notrace static cycle_t vread_tsc(void)
	{
	cycle_t ret;
	u64 last;

	/*
	* Empirically, a fence (of type that depends on the CPU)
	* before rdtsc is enough to ensure that rdtsc is ordered
	* with respect to loads. The various CPU manuals are unclear
	* as to whether rdtsc can be reordered with later loads,
	* but no one has ever seen it happen.
	*/
	rdtsc_barrier();
	ret = (cycle_t)vget_cycles();

	last = VVAR(vsyscall_gtod_data).clock.cycle_last;

	if (likely(ret >= last))
	return ret;

	/*
	* GCC likes to generate cmov here, but this branch is extremely
	* predictable (it's just a funciton of time and the likely is
	* very likely) and there's a data dependence, so force GCC
	* to generate a branch instead. I don't barrier() because
	* we don't actually need a barrier, and if this function
	* ever gets inlined it will generate worse code.
	*/
	asm volatile ("");
	return last;
	}

	static notrace cycle_t vread_hpet(void)
	{
	return readl((const void __iomem *)fix_to_virt(VSYSCALL_HPET) + HPET_COUNTER);
	}

	#ifdef CONFIG_PARAVIRT_CLOCK

	static notrace const struct pvclock_vsyscall_time_info *get_pvti(int cpu)
	{
	const struct pvclock_vsyscall_time_info *pvti_base;
	int idx = cpu / (PAGE_SIZE/PVTI_SIZE);
	int offset = cpu % (PAGE_SIZE/PVTI_SIZE);

	BUG_ON(PVCLOCK_FIXMAP_BEGIN + idx > PVCLOCK_FIXMAP_END);

	pvti_base = (struct pvclock_vsyscall_time_info *)
	__fix_to_virt(PVCLOCK_FIXMAP_BEGIN+idx);

	return &pvti_base[offset];
	}

	static notrace cycle_t vread_pvclock(int *mode)
	{
	const struct pvclock_vsyscall_time_info *pvti;
	cycle_t ret;
	u64 last;
	u32 version;
	u32 migrate_count;
	u8 flags;
	unsigned cpu, cpu1;


	/*
	* When looping to get a consistent (time-info, tsc) pair, we
	* also need to deal with the possibility we can switch vcpus,
	* so make sure we always re-fetch time-info for the current vcpu.
	*/
	do {
	cpu = __getcpu() & VGETCPU_CPU_MASK;
	/* TODO: We can put vcpu id into higher bits of pvti.version.
	* This will save a couple of cycles by getting rid of
	* __getcpu() calls (Gleb).
	*/

	pvti = get_pvti(cpu);

	migrate_count = pvti->migrate_count;

	version = __pvclock_read_cycles(&pvti->pvti, &ret, &flags);

	/*
	* Test we're still on the cpu as well as the version.
	* We could have been migrated just after the first
	* vgetcpu but before fetching the version, so we
	* wouldn't notice a version change.
	*/
	cpu1 = __getcpu() & VGETCPU_CPU_MASK;
	} while (unlikely(cpu != cpu1 \|\|
	(pvti->pvti.version & 1) \|\|
	pvti->pvti.version != version \|\|
	pvti->migrate_count != migrate_count));

	if (unlikely(!(flags & PVCLOCK_TSC_STABLE_BIT)))
	*mode = VCLOCK_NONE;

	/* refer to tsc.c read_tsc() comment for rationale */
	last = VVAR(vsyscall_gtod_data).clock.cycle_last;

	if (likely(ret >= last))
	return ret;

	return last;
	}
	#endif

	notrace static long vdso_fallback_gettime(long clock, struct timespec *ts)
	{
	long ret;
	asm("syscall" : "=a" (ret) :
	"0" (__NR_clock_gettime),"D" (clock), "S" (ts) : "memory");
	return ret;
	}

	notrace static long vdso_fallback_gtod(struct timeval tv, struct timezone tz)
	{
	long ret;

	asm("syscall" : "=a" (ret) :
	"0" (__NR_gettimeofday), "D" (tv), "S" (tz) : "memory");
	return ret;
	}


	notrace static inline u64 vgetsns(int *mode)
	{
	long v;
	cycles_t cycles;
	if (gtod->clock.vclock_mode == VCLOCK_TSC)
	cycles = vread_tsc();
	else if (gtod->clock.vclock_mode == VCLOCK_HPET)
	cycles = vread_hpet();
	#ifdef CONFIG_PARAVIRT_CLOCK
	else if (gtod->clock.vclock_mode == VCLOCK_PVCLOCK)
	cycles = vread_pvclock(mode);
	#endif
	else
	return 0;
	v = (cycles - gtod->clock.cycle_last) & gtod->clock.mask;
	return v * gtod->clock.mult;
	}

	/* Code size doesn't matter (vdso is 4k anyway) and this is faster. */
	notrace static int __always_inline do_realtime(struct timespec *ts)
	{
	unsigned long seq;
	u64 ns;
	int mode;

	ts->tv_nsec = 0;
	do {
	seq = read_seqcount_begin(&gtod->seq);
	mode = gtod->clock.vclock_mode;
	ts->tv_sec = gtod->wall_time_sec;
	ns = gtod->wall_time_snsec;
	ns += vgetsns(&mode);
	ns >>= gtod->clock.shift;
	} while (unlikely(read_seqcount_retry(&gtod->seq, seq)));

	timespec_add_ns(ts, ns);
	return mode;
	}

	notrace static int do_monotonic(struct timespec *ts)
	{
	unsigned long seq;
	u64 ns;
	int mode;

	ts->tv_nsec = 0;
	do {
	seq = read_seqcount_begin(&gtod->seq);
	mode = gtod->clock.vclock_mode;
	ts->tv_sec = gtod->monotonic_time_sec;
	ns = gtod->monotonic_time_snsec;
	ns += vgetsns(&mode);
	ns >>= gtod->clock.shift;
	} while (unlikely(read_seqcount_retry(&gtod->seq, seq)));
	timespec_add_ns(ts, ns);

	return mode;
	}

	notrace static int do_realtime_coarse(struct timespec *ts)
	{
	unsigned long seq;
	do {
	seq = read_seqcount_begin(&gtod->seq);
	ts->tv_sec = gtod->wall_time_coarse.tv_sec;
	ts->tv_nsec = gtod->wall_time_coarse.tv_nsec;
	} while (unlikely(read_seqcount_retry(&gtod->seq, seq)));
	return 0;
	}

	notrace static int do_monotonic_coarse(struct timespec *ts)
	{
	unsigned long seq;
	do {
	seq = read_seqcount_begin(&gtod->seq);
	ts->tv_sec = gtod->monotonic_time_coarse.tv_sec;
	ts->tv_nsec = gtod->monotonic_time_coarse.tv_nsec;
	} while (unlikely(read_seqcount_retry(&gtod->seq, seq)));

	return 0;
	}

	notrace int __vdso_clock_gettime(clockid_t clock, struct timespec *ts)
	{
	int ret = VCLOCK_NONE;

	switch (clock) {
	case CLOCK_REALTIME:
	ret = do_realtime(ts);
	break;
	case CLOCK_MONOTONIC:
	ret = do_monotonic(ts);
	break;
	case CLOCK_REALTIME_COARSE:
	return do_realtime_coarse(ts);
	case CLOCK_MONOTONIC_COARSE:
	return do_monotonic_coarse(ts);
	}

	if (ret == VCLOCK_NONE)
	return vdso_fallback_gettime(clock, ts);
	return 0;
	}
	int clock_gettime(clockid_t, struct timespec *)
	__attribute__((weak, alias("__vdso_clock_gettime")));

	notrace int __vdso_gettimeofday(struct timeval tv, struct timezone tz)
	{
	long ret = VCLOCK_NONE;

	if (likely(tv != NULL)) {
	BUILD_BUG_ON(offsetof(struct timeval, tv_usec) !=
	offsetof(struct timespec, tv_nsec) \|\|
	sizeof(*tv) != sizeof(struct timespec));
	ret = do_realtime((struct timespec *)tv);
	tv->tv_usec /= 1000;
	}
	if (unlikely(tz != NULL)) {
	/* Avoid memcpy. Some old compilers fail to inline it */
	tz->tz_minuteswest = gtod->sys_tz.tz_minuteswest;
	tz->tz_dsttime = gtod->sys_tz.tz_dsttime;
	}

	if (ret == VCLOCK_NONE)
	return vdso_fallback_gtod(tv, tz);
	return 0;
	}
	int gettimeofday(struct timeval , struct timezone )
	__attribute__((weak, alias("__vdso_gettimeofday")));

	/*
	* This will break when the xtime seconds get inaccurate, but that is
	* unlikely
	*/
	notrace time_t __vdso_time(time_t *t)
	{
	/* This is atomic on x86_64 so we don't need any locks. */
	time_t result = ACCESS_ONCE(VVAR(vsyscall_gtod_data).wall_time_sec);

	if (t)
	*t = result;
	return result;
	}
	int time(time_t *t)
	__attribute__((weak, alias("__vdso_time")));