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 #include <asm/vgtod.h>
  29
  30 static u8 valid_flags __read_mostly = 0;
  31 static struct pvclock_vsyscall_time_info *pvti_cpu0_va __read_mostly;
  32
  33 void pvclock_set_flags(u8 flags)
  34 {
  35         valid_flags = flags;
  36 }
  37
  38 unsigned long pvclock_tsc_khz(struct pvclock_vcpu_time_info *src)
  39 {
  40         u64 pv_tsc_khz = 1000000ULL << 32;
  41
  42         do_div(pv_tsc_khz, src->tsc_to_system_mul);
  43         if (src->tsc_shift < 0)
  44                 pv_tsc_khz <<= -src->tsc_shift;
  45         else
  46                 pv_tsc_khz >>= src->tsc_shift;
  47         return pv_tsc_khz;
  48 }
  49
  50 void pvclock_touch_watchdogs(void)
  51 {
  52         touch_softlockup_watchdog_sync();
  53         clocksource_touch_watchdog();
  54         rcu_cpu_stall_reset();
  55         reset_hung_task_detector();
  56 }
  57
  58 static atomic64_t last_value = ATOMIC64_INIT(0);
  59
  60 void pvclock_resume(void)
  61 {
  62         atomic64_set(&last_value, 0);
  63 }
  64
  65 u8 pvclock_read_flags(struct pvclock_vcpu_time_info *src)
  66 {
  67         unsigned version;
  68         u8 flags;
  69
  70         do {
  71                 version = pvclock_read_begin(src);
  72                 flags = src->flags;
  73         } while (pvclock_read_retry(src, version));
  74
  75         return flags & valid_flags;
  76 }
  77
  78 u64 pvclock_clocksource_read(struct pvclock_vcpu_time_info *src)
  79 {
  80         unsigned version;
  81         u64 ret;
  82         u64 last;
  83         u8 flags;
  84
  85         do {
  86                 version = pvclock_read_begin(src);
  87                 ret = __pvclock_read_cycles(src, rdtsc_ordered());
  88                 flags = src->flags;
  89         } while (pvclock_read_retry(src, version));
  90
  91         if (unlikely((flags & PVCLOCK_GUEST_STOPPED) != 0)) {
  92                 src->flags &= ~PVCLOCK_GUEST_STOPPED;
  93                 pvclock_touch_watchdogs();
  94         }
  95
  96         if ((valid_flags & PVCLOCK_TSC_STABLE_BIT) &&
  97                 (flags & PVCLOCK_TSC_STABLE_BIT))
  98                 return ret;
  99
 100         /*
 101          * Assumption here is that last_value, a global accumulator, always goes
 102          * forward. If we are less than that, we should not be much smaller.
 103          * We assume there is an error marging we're inside, and then the correction
 104          * does not sacrifice accuracy.
 105          *
 106          * For reads: global may have changed between test and return,
 107          * but this means someone else updated poked the clock at a later time.
 108          * We just need to make sure we are not seeing a backwards event.
 109          *
 110          * For updates: last_value = ret is not enough, since two vcpus could be
 111          * updating at the same time, and one of them could be slightly behind,
 112          * making the assumption that last_value always go forward fail to hold.
 113          */
 114         last = atomic64_read(&last_value);
 115         do {
 116                 if (ret < last)
 117                         return last;
 118                 last = atomic64_cmpxchg(&last_value, last, ret);
 119         } while (unlikely(last != ret));
 120
 121         return ret;
 122 }
 123
 124 void pvclock_read_wallclock(struct pvclock_wall_clock *wall_clock,
 125                             struct pvclock_vcpu_time_info *vcpu_time,
 126                             struct timespec *ts)
 127 {
 128         u32 version;
 129         u64 delta;
 130         struct timespec now;
 131
 132         /* get wallclock at system boot */
 133         do {
 134                 version = wall_clock->version;
 135                 rmb();          /* fetch version before time */
 136                 now.tv_sec  = wall_clock->sec;
 137                 now.tv_nsec = wall_clock->nsec;
 138                 rmb();          /* fetch time before checking version */
 139         } while ((wall_clock->version & 1) || (version != wall_clock->version));
 140
 141         delta = pvclock_clocksource_read(vcpu_time);    /* time since system boot */
 142         delta += now.tv_sec * (u64)NSEC_PER_SEC + now.tv_nsec;
 143
 144         now.tv_nsec = do_div(delta, NSEC_PER_SEC);
 145         now.tv_sec = delta;
 146
 147         set_normalized_timespec(ts, now.tv_sec, now.tv_nsec);
 148 }
 149
 150 void pvclock_set_pvti_cpu0_va(struct pvclock_vsyscall_time_info *pvti)
 151 {
 152         WARN_ON(vclock_was_used(VCLOCK_PVCLOCK));
 153         pvti_cpu0_va = pvti;
 154 }
 155
 156 struct pvclock_vsyscall_time_info *pvclock_get_pvti_cpu0_va(void)
 157 {
 158         return pvti_cpu0_va;
 159 }
 160 EXPORT_SYMBOL_GPL(pvclock_get_pvti_cpu0_va);