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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 <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);
161 

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