LXR linux/arch/x86/kernel/pvclock.c

   1// SPDX-License-Identifier: GPL-2.0-or-later
   2/*  paravirtual clock -- common code used by kvm/xen
   3
   4*/
   5
   6#include <linux/clocksource.h>
   7#include <linux/kernel.h>
   8#include <linux/percpu.h>
   9#include <linux/notifier.h>
  10#include <linux/sched.h>
  11#include <linux/gfp.h>
  12#include <linux/memblock.h>
  13#include <linux/nmi.h>
  14
  15#include <asm/fixmap.h>
  16#include <asm/pvclock.h>
  17#include <asm/vgtod.h>
  18
  19static u8 valid_flags __read_mostly = 0;
  20static struct pvclock_vsyscall_time_info *pvti_cpu0_va __read_mostly;
  21
  22void pvclock_set_flags(u8 flags)
  23{
  24        valid_flags = flags;
  25}
  26
  27unsigned long pvclock_tsc_khz(struct pvclock_vcpu_time_info *src)
  28{
  29        u64 pv_tsc_khz = 1000000ULL << 32;
  30
  31        do_div(pv_tsc_khz, src->tsc_to_system_mul);
  32        if (src->tsc_shift < 0)
  33                pv_tsc_khz <<= -src->tsc_shift;
  34        else
  35                pv_tsc_khz >>= src->tsc_shift;
  36        return pv_tsc_khz;
  37}
  38
  39void pvclock_touch_watchdogs(void)
  40{
  41        touch_softlockup_watchdog_sync();
  42        clocksource_touch_watchdog();
  43        rcu_cpu_stall_reset();
  44        reset_hung_task_detector();
  45}
  46
  47static atomic64_t last_value = ATOMIC64_INIT(0);
  48
  49void pvclock_resume(void)
  50{
  51        atomic64_set(&last_value, 0);
  52}
  53
  54u8 pvclock_read_flags(struct pvclock_vcpu_time_info *src)
  55{
  56        unsigned version;
  57        u8 flags;
  58
  59        do {
  60                version = pvclock_read_begin(src);
  61                flags = src->flags;
  62        } while (pvclock_read_retry(src, version));
  63
  64        return flags & valid_flags;
  65}
  66
  67u64 pvclock_clocksource_read(struct pvclock_vcpu_time_info *src)
  68{
  69        unsigned version;
  70        u64 ret;
  71        u64 last;
  72        u8 flags;
  73
  74        do {
  75                version = pvclock_read_begin(src);
  76                ret = __pvclock_read_cycles(src, rdtsc_ordered());
  77                flags = src->flags;
  78        } while (pvclock_read_retry(src, version));
  79
  80        if (unlikely((flags & PVCLOCK_GUEST_STOPPED) != 0)) {
  81                src->flags &= ~PVCLOCK_GUEST_STOPPED;
  82                pvclock_touch_watchdogs();
  83        }
  84
  85        if ((valid_flags & PVCLOCK_TSC_STABLE_BIT) &&
  86                (flags & PVCLOCK_TSC_STABLE_BIT))
  87                return ret;
  88
  89        /*
  90         * Assumption here is that last_value, a global accumulator, always goes
  91         * forward. If we are less than that, we should not be much smaller.
  92         * We assume there is an error marging we're inside, and then the correction
  93         * does not sacrifice accuracy.
  94         *
  95         * For reads: global may have changed between test and return,
  96         * but this means someone else updated poked the clock at a later time.
  97         * We just need to make sure we are not seeing a backwards event.
  98         *
  99         * For updates: last_value = ret is not enough, since two vcpus could be
 100         * updating at the same time, and one of them could be slightly behind,
 101         * making the assumption that last_value always go forward fail to hold.
 102         */
 103        last = atomic64_read(&last_value);
 104        do {
 105                if (ret < last)
 106                        return last;
 107                last = atomic64_cmpxchg(&last_value, last, ret);
 108        } while (unlikely(last != ret));
 109
 110        return ret;
 111}
 112
 113void pvclock_read_wallclock(struct pvclock_wall_clock *wall_clock,
 114                            struct pvclock_vcpu_time_info *vcpu_time,
 115                            struct timespec64 *ts)
 116{
 117        u32 version;
 118        u64 delta;
 119        struct timespec64 now;
 120
 121        /* get wallclock at system boot */
 122        do {
 123                version = wall_clock->version;
 124                rmb();          /* fetch version before time */
 125                /*
 126                 * Note: wall_clock->sec is a u32 value, so it can
 127                 * only store dates between 1970 and 2106. To allow
 128                 * times beyond that, we need to create a new hypercall
 129                 * interface with an extended pvclock_wall_clock structure
 130                 * like ARM has.
 131                 */
 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 * 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_timespec64(ts, now.tv_sec, now.tv_nsec);
 144}
 145
 146void pvclock_set_pvti_cpu0_va(struct pvclock_vsyscall_time_info *pvti)
 147{
 148        WARN_ON(vclock_was_used(VDSO_CLOCKMODE_PVCLOCK));
 149        pvti_cpu0_va = pvti;
 150}
 151
 152struct pvclock_vsyscall_time_info *pvclock_get_pvti_cpu0_va(void)
 153{
 154        return pvti_cpu0_va;
 155}
 156EXPORT_SYMBOL_GPL(pvclock_get_pvti_cpu0_va);
 157