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 static atomic64_t last_value = ATOMIC64_INIT(0);
  47
  48 void pvclock_resume(void)
  49 {
  50         atomic64_set(&last_value, 0);
  51 }
  52
  53 u8 pvclock_read_flags(struct pvclock_vcpu_time_info *src)
  54 {
  55         unsigned version;
  56         cycle_t ret;
  57         u8 flags;
  58
  59         do {
  60                 version = __pvclock_read_cycles(src, &ret, &flags);
  61         } while ((src->version & 1) || version != src->version);
  62
  63         return flags & valid_flags;
  64 }
  65
  66 cycle_t pvclock_clocksource_read(struct pvclock_vcpu_time_info *src)
  67 {
  68         unsigned version;
  69         cycle_t ret;
  70         u64 last;
  71         u8 flags;
  72
  73         do {
  74                 version = __pvclock_read_cycles(src, &ret, &flags);
  75         } while ((src->version & 1) || version != src->version);
  76
  77         if ((valid_flags & PVCLOCK_TSC_STABLE_BIT) &&
  78                 (flags & PVCLOCK_TSC_STABLE_BIT))
  79                 return ret;
  80
  81         /*
  82          * Assumption here is that last_value, a global accumulator, always goes
  83          * forward. If we are less than that, we should not be much smaller.
  84          * We assume there is an error marging we're inside, and then the correction
  85          * does not sacrifice accuracy.
  86          *
  87          * For reads: global may have changed between test and return,
  88          * but this means someone else updated poked the clock at a later time.
  89          * We just need to make sure we are not seeing a backwards event.
  90          *
  91          * For updates: last_value = ret is not enough, since two vcpus could be
  92          * updating at the same time, and one of them could be slightly behind,
  93          * making the assumption that last_value always go forward fail to hold.
  94          */
  95         last = atomic64_read(&last_value);
  96         do {
  97                 if (ret < last)
  98                         return last;
  99                 last = atomic64_cmpxchg(&last_value, last, ret);
 100         } while (unlikely(last != ret));
 101
 102         return ret;
 103 }
 104
 105 void pvclock_read_wallclock(struct pvclock_wall_clock *wall_clock,
 106                             struct pvclock_vcpu_time_info *vcpu_time,
 107                             struct timespec *ts)
 108 {
 109         u32 version;
 110         u64 delta;
 111         struct timespec now;
 112
 113         /* get wallclock at system boot */
 114         do {
 115                 version = wall_clock->version;
 116                 rmb();          /* fetch version before time */
 117                 now.tv_sec  = wall_clock->sec;
 118                 now.tv_nsec = wall_clock->nsec;
 119                 rmb();          /* fetch time before checking version */
 120         } while ((wall_clock->version & 1) || (version != wall_clock->version));
 121
 122         delta = pvclock_clocksource_read(vcpu_time);    /* time since system boot */
 123         delta += now.tv_sec * (u64)NSEC_PER_SEC + now.tv_nsec;
 124
 125         now.tv_nsec = do_div(delta, NSEC_PER_SEC);
 126         now.tv_sec = delta;
 127
 128         set_normalized_timespec(ts, now.tv_sec, now.tv_nsec);
 129 }
 130
 131 #ifdef CONFIG_X86_64
 132 /*
 133  * Initialize the generic pvclock vsyscall state.  This will allocate
 134  * a/some page(s) for the per-vcpu pvclock information, set up a
 135  * fixmap mapping for the page(s)
 136  */
 137
 138 int __init pvclock_init_vsyscall(struct pvclock_vsyscall_time_info *i,
 139                                  int size)
 140 {
 141         int idx;
 142
 143         WARN_ON (size != PVCLOCK_VSYSCALL_NR_PAGES*PAGE_SIZE);
 144
 145         for (idx = 0; idx <= (PVCLOCK_FIXMAP_END-PVCLOCK_FIXMAP_BEGIN); idx++) {
 146                 __set_fixmap(PVCLOCK_FIXMAP_BEGIN + idx,
 147                              __pa(i) + (idx*PAGE_SIZE),
 148                              PAGE_KERNEL_VVAR);
 149         }
 150
 151         return 0;
 152 }
 153 #endif