LXR linux/arch/x86/kernel/pvclock.c

   1/*  paravirtual clock -- common code used by kvm/xen
   2
   3    This program is free software; you can redistribute it and/or modify
   4    it under the terms of the GNU General Public License as published by
   5    the Free Software Foundation; either version 2 of the License, or
   6    (at your option) any later version.
   7
   8    This program is distributed in the hope that it will be useful,
   9    but WITHOUT ANY WARRANTY; without even the implied warranty of
  10    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  11    GNU General Public License for more details.
  12
  13    You should have received a copy of the GNU General Public License
  14    along with this program; if not, write to the Free Software
  15    Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA  02110-1301  USA
  16*/
  17
  18#include <linux/kernel.h>
  19#include <linux/percpu.h>
  20#include <linux/notifier.h>
  21#include <linux/sched.h>
  22#include <linux/gfp.h>
  23#include <linux/bootmem.h>
  24#include <linux/nmi.h>
  25
  26#include <asm/fixmap.h>
  27#include <asm/pvclock.h>
  28
  29static u8 valid_flags __read_mostly = 0;
  30
  31void pvclock_set_flags(u8 flags)
  32{
  33        valid_flags = flags;
  34}
  35
  36unsigned long pvclock_tsc_khz(struct pvclock_vcpu_time_info *src)
  37{
  38        u64 pv_tsc_khz = 1000000ULL << 32;
  39
  40        do_div(pv_tsc_khz, src->tsc_to_system_mul);
  41        if (src->tsc_shift < 0)
  42                pv_tsc_khz <<= -src->tsc_shift;
  43        else
  44                pv_tsc_khz >>= src->tsc_shift;
  45        return pv_tsc_khz;
  46}
  47
  48void pvclock_touch_watchdogs(void)
  49{
  50        touch_softlockup_watchdog_sync();
  51        clocksource_touch_watchdog();
  52        rcu_cpu_stall_reset();
  53        reset_hung_task_detector();
  54}
  55
  56static atomic64_t last_value = ATOMIC64_INIT(0);
  57
  58void pvclock_resume(void)
  59{
  60        atomic64_set(&last_value, 0);
  61}
  62
  63u8 pvclock_read_flags(struct pvclock_vcpu_time_info *src)
  64{
  65        unsigned version;
  66        u8 flags;
  67
  68        do {
  69                version = pvclock_read_begin(src);
  70                flags = src->flags;
  71        } while (pvclock_read_retry(src, version));
  72
  73        return flags & valid_flags;
  74}
  75
  76u64 pvclock_clocksource_read(struct pvclock_vcpu_time_info *src)
  77{
  78        unsigned version;
  79        u64 ret;
  80        u64 last;
  81        u8 flags;
  82
  83        do {
  84                version = pvclock_read_begin(src);
  85                ret = __pvclock_read_cycles(src, rdtsc_ordered());
  86                flags = src->flags;
  87        } while (pvclock_read_retry(src, version));
  88
  89        if (unlikely((flags & PVCLOCK_GUEST_STOPPED) != 0)) {
  90                src->flags &= ~PVCLOCK_GUEST_STOPPED;
  91                pvclock_touch_watchdogs();
  92        }
  93
  94        if ((valid_flags & PVCLOCK_TSC_STABLE_BIT) &&
  95                (flags & PVCLOCK_TSC_STABLE_BIT))
  96                return ret;
  97
  98        /*
  99         * Assumption here is that last_value, a global accumulator, always goes
 100         * forward. If we are less than that, we should not be much smaller.
 101         * We assume there is an error marging we're inside, and then the correction
 102         * does not sacrifice accuracy.
 103         *
 104         * For reads: global may have changed between test and return,
 105         * but this means someone else updated poked the clock at a later time.
 106         * We just need to make sure we are not seeing a backwards event.
 107         *
 108         * For updates: last_value = ret is not enough, since two vcpus could be
 109         * updating at the same time, and one of them could be slightly behind,
 110         * making the assumption that last_value always go forward fail to hold.
 111         */
 112        last = atomic64_read(&last_value);
 113        do {
 114                if (ret < last)
 115                        return last;
 116                last = atomic64_cmpxchg(&last_value, last, ret);
 117        } while (unlikely(last != ret));
 118
 119        return ret;
 120}
 121
 122void pvclock_read_wallclock(struct pvclock_wall_clock *wall_clock,
 123                            struct pvclock_vcpu_time_info *vcpu_time,
 124                            struct timespec *ts)
 125{
 126        u32 version;
 127        u64 delta;
 128        struct timespec now;
 129
 130        /* get wallclock at system boot */
 131        do {
 132                version = wall_clock->version;
 133                rmb();          /* fetch version before time */
 134                now.tv_sec  = wall_clock->sec;
 135                now.tv_nsec = wall_clock->nsec;
 136                rmb();          /* fetch time before checking version */
 137        } while ((wall_clock->version & 1) || (version != wall_clock->version));
 138
 139        delta = pvclock_clocksource_read(vcpu_time);    /* time since system boot */
 140        delta += now.tv_sec * (u64)NSEC_PER_SEC + now.tv_nsec;
 141
 142        now.tv_nsec = do_div(delta, NSEC_PER_SEC);
 143        now.tv_sec = delta;
 144
 145        set_normalized_timespec(ts, now.tv_sec, now.tv_nsec);
 146}
 147