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 <asm/fixmap.h>
  25 #include <asm/pvclock.h>
  26
  27 static u8 valid_flags __read_mostly = 0;
  28
  29 void pvclock_set_flags(u8 flags)
  30 {
  31         valid_flags = flags;
  32 }
  33
  34 unsigned long pvclock_tsc_khz(struct pvclock_vcpu_time_info *src)
  35 {
  36         u64 pv_tsc_khz = 1000000ULL << 32;
  37
  38         do_div(pv_tsc_khz, src->tsc_to_system_mul);
  39         if (src->tsc_shift < 0)
  40                 pv_tsc_khz <<= -src->tsc_shift;
  41         else
  42                 pv_tsc_khz >>= src->tsc_shift;
  43         return pv_tsc_khz;
  44 }
  45
  46 void pvclock_touch_watchdogs(void)
  47 {
  48         touch_softlockup_watchdog_sync();
  49         clocksource_touch_watchdog();
  50         rcu_cpu_stall_reset();
  51         reset_hung_task_detector();
  52 }
  53
  54 static atomic64_t last_value = ATOMIC64_INIT(0);
  55
  56 void pvclock_resume(void)
  57 {
  58         atomic64_set(&last_value, 0);
  59 }
  60
  61 u8 pvclock_read_flags(struct pvclock_vcpu_time_info *src)
  62 {
  63         unsigned version;
  64         cycle_t ret;
  65         u8 flags;
  66
  67         do {
  68                 version = __pvclock_read_cycles(src, &ret, &flags);
  69         } while ((src->version & 1) || version != src->version);
  70
  71         return flags & valid_flags;
  72 }
  73
  74 cycle_t pvclock_clocksource_read(struct pvclock_vcpu_time_info *src)
  75 {
  76         unsigned version;
  77         cycle_t ret;
  78         u64 last;
  79         u8 flags;
  80
  81         do {
  82                 version = __pvclock_read_cycles(src, &ret, &flags);
  83         } while ((src->version & 1) || version != src->version);
  84
  85         if (unlikely((flags & PVCLOCK_GUEST_STOPPED) != 0)) {
  86                 src->flags &= ~PVCLOCK_GUEST_STOPPED;
  87                 pvclock_touch_watchdogs();
  88         }
  89
  90         if ((valid_flags & PVCLOCK_TSC_STABLE_BIT) &&
  91                 (flags & PVCLOCK_TSC_STABLE_BIT))
  92                 return ret;
  93
  94         /*
  95          * Assumption here is that last_value, a global accumulator, always goes
  96          * forward. If we are less than that, we should not be much smaller.
  97          * We assume there is an error marging we're inside, and then the correction
  98          * does not sacrifice accuracy.
  99          *
 100          * For reads: global may have changed between test and return,
 101          * but this means someone else updated poked the clock at a later time.
 102          * We just need to make sure we are not seeing a backwards event.
 103          *
 104          * For updates: last_value = ret is not enough, since two vcpus could be
 105          * updating at the same time, and one of them could be slightly behind,
 106          * making the assumption that last_value always go forward fail to hold.
 107          */
 108         last = atomic64_read(&last_value);
 109         do {
 110                 if (ret < last)
 111                         return last;
 112                 last = atomic64_cmpxchg(&last_value, last, ret);
 113         } while (unlikely(last != ret));
 114
 115         return ret;
 116 }
 117
 118 void pvclock_read_wallclock(struct pvclock_wall_clock *wall_clock,
 119                             struct pvclock_vcpu_time_info *vcpu_time,
 120                             struct timespec *ts)
 121 {
 122         u32 version;
 123         u64 delta;
 124         struct timespec now;
 125
 126         /* get wallclock at system boot */
 127         do {
 128                 version = wall_clock->version;
 129                 rmb();          /* fetch version before time */
 130                 now.tv_sec  = wall_clock->sec;
 131                 now.tv_nsec = wall_clock->nsec;
 132                 rmb();          /* fetch time before checking version */
 133         } while ((wall_clock->version & 1) || (version != wall_clock->version));
 134
 135         delta = pvclock_clocksource_read(vcpu_time);    /* time since system boot */
 136         delta += now.tv_sec * (u64)NSEC_PER_SEC + now.tv_nsec;
 137
 138         now.tv_nsec = do_div(delta, NSEC_PER_SEC);
 139         now.tv_sec = delta;
 140
 141         set_normalized_timespec(ts, now.tv_sec, now.tv_nsec);
 142 }