LXR linux/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
  27static u8 valid_flags __read_mostly = 0;
  28
  29void pvclock_set_flags(u8 flags)
  30{
  31        valid_flags = flags;
  32}
  33
  34unsigned 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
  46void 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
  54static atomic64_t last_value = ATOMIC64_INIT(0);
  55
  56void pvclock_resume(void)
  57{
  58        atomic64_set(&last_value, 0);
  59}
  60
  61u8 pvclock_read_flags(struct pvclock_vcpu_time_info *src)
  62{
  63        unsigned version;
  64        u8 flags;
  65
  66        do {
  67                version = pvclock_read_begin(src);
  68                flags = src->flags;
  69        } while (pvclock_read_retry(src, version));
  70
  71        return flags & valid_flags;
  72}
  73
  74u64 pvclock_clocksource_read(struct pvclock_vcpu_time_info *src)
  75{
  76        unsigned version;
  77        u64 ret;
  78        u64 last;
  79        u8 flags;
  80
  81        do {
  82                version = pvclock_read_begin(src);
  83                ret = __pvclock_read_cycles(src, rdtsc_ordered());
  84                flags = src->flags;
  85        } while (pvclock_read_retry(src, version));
  86
  87        if (unlikely((flags & PVCLOCK_GUEST_STOPPED) != 0)) {
  88                src->flags &= ~PVCLOCK_GUEST_STOPPED;
  89                pvclock_touch_watchdogs();
  90        }
  91
  92        if ((valid_flags & PVCLOCK_TSC_STABLE_BIT) &&
  93                (flags & PVCLOCK_TSC_STABLE_BIT))
  94                return ret;
  95
  96        /*
  97         * Assumption here is that last_value, a global accumulator, always goes
  98         * forward. If we are less than that, we should not be much smaller.
  99         * We assume there is an error marging we're inside, and then the correction
 100         * does not sacrifice accuracy.
 101         *
 102         * For reads: global may have changed between test and return,
 103         * but this means someone else updated poked the clock at a later time.
 104         * We just need to make sure we are not seeing a backwards event.
 105         *
 106         * For updates: last_value = ret is not enough, since two vcpus could be
 107         * updating at the same time, and one of them could be slightly behind,
 108         * making the assumption that last_value always go forward fail to hold.
 109         */
 110        last = atomic64_read(&last_value);
 111        do {
 112                if (ret < last)
 113                        return last;
 114                last = atomic64_cmpxchg(&last_value, last, ret);
 115        } while (unlikely(last != ret));
 116
 117        return ret;
 118}
 119
 120void pvclock_read_wallclock(struct pvclock_wall_clock *wall_clock,
 121                            struct pvclock_vcpu_time_info *vcpu_time,
 122                            struct timespec *ts)
 123{
 124        u32 version;
 125        u64 delta;
 126        struct timespec now;
 127
 128        /* get wallclock at system boot */
 129        do {
 130                version = wall_clock->version;
 131                rmb();          /* fetch version before time */
 132                now.tv_sec  = wall_clock->sec;
 133                now.tv_nsec = wall_clock->nsec;
 134                rmb();          /* fetch time before checking version */
 135        } while ((wall_clock->version & 1) || (version != wall_clock->version));
 136
 137        delta = pvclock_clocksource_read(vcpu_time);    /* time since system boot */
 138        delta += now.tv_sec * (u64)NSEC_PER_SEC + now.tv_nsec;
 139
 140        now.tv_nsec = do_div(delta, NSEC_PER_SEC);
 141        now.tv_sec = delta;
 142
 143        set_normalized_timespec(ts, now.tv_sec, now.tv_nsec);
 144}
 145
 146#ifdef CONFIG_X86_64
 147/*
 148 * Initialize the generic pvclock vsyscall state.  This will allocate
 149 * a/some page(s) for the per-vcpu pvclock information, set up a
 150 * fixmap mapping for the page(s)
 151 */
 152
 153int __init pvclock_init_vsyscall(struct pvclock_vsyscall_time_info *i,
 154                                 int size)
 155{
 156        int idx;
 157
 158        WARN_ON (size != PVCLOCK_VSYSCALL_NR_PAGES*PAGE_SIZE);
 159
 160        for (idx = 0; idx <= (PVCLOCK_FIXMAP_END-PVCLOCK_FIXMAP_BEGIN); idx++) {
 161                __set_fixmap(PVCLOCK_FIXMAP_BEGIN + idx,
 162                             __pa(i) + (idx*PAGE_SIZE),
 163                             PAGE_KERNEL_VVAR);
 164        }
 165
 166        return 0;
 167}
 168#endif
 169