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Linux/arch/x86/kernel/pvclock.c

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  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                 /* Make sure that the version double-check is last. */
 70                 smp_rmb();
 71         } while ((src->version & 1) || version != src->version);
 72 
 73         return flags & valid_flags;
 74 }
 75 
 76 cycle_t pvclock_clocksource_read(struct pvclock_vcpu_time_info *src)
 77 {
 78         unsigned version;
 79         cycle_t ret;
 80         u64 last;
 81         u8 flags;
 82 
 83         do {
 84                 version = __pvclock_read_cycles(src, &ret, &flags);
 85                 /* Make sure that the version double-check is last. */
 86                 smp_rmb();
 87         } while ((src->version & 1) || version != 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 
122 void 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 

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