![Paolo Bonzini](/assets/img/avatar_default.png)
Introduce a function that reads the exact nanoseconds value that is provided to the guest in kvmclock. This crystallizes the notion of kvmclock as a thin veneer over a stable TSC, that the guest will (hopefully) convert with NTP. In other words, kvmclock is *not* a paravirtualized host-to-guest NTP. Drop the get_kernel_ns() function, that was used both to get the base value of the master clock and to get the current value of kvmclock. The former use is replaced by ktime_get_boot_ns(), the latter is the purpose of get_kernel_ns(). This also allows KVM to provide a Hyper-V time reference counter that is synchronized with the time that is computed from the TSC page. Reviewed-by: Roman Kagan <rkagan@virtuozzo.com> Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
145 lines
3.9 KiB
C
145 lines
3.9 KiB
C
/* paravirtual clock -- common code used by kvm/xen
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This program is free software; you can redistribute it and/or modify
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it under the terms of the GNU General Public License as published by
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the Free Software Foundation; either version 2 of the License, or
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(at your option) any later version.
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This program is distributed in the hope that it will be useful,
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but WITHOUT ANY WARRANTY; without even the implied warranty of
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MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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GNU General Public License for more details.
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You should have received a copy of the GNU General Public License
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along with this program; if not, write to the Free Software
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Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA
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*/
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#include <linux/kernel.h>
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#include <linux/percpu.h>
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#include <linux/notifier.h>
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#include <linux/sched.h>
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#include <linux/gfp.h>
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#include <linux/bootmem.h>
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#include <asm/fixmap.h>
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#include <asm/pvclock.h>
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static u8 valid_flags __read_mostly = 0;
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void pvclock_set_flags(u8 flags)
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{
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valid_flags = flags;
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}
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unsigned long pvclock_tsc_khz(struct pvclock_vcpu_time_info *src)
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{
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u64 pv_tsc_khz = 1000000ULL << 32;
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do_div(pv_tsc_khz, src->tsc_to_system_mul);
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if (src->tsc_shift < 0)
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pv_tsc_khz <<= -src->tsc_shift;
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else
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pv_tsc_khz >>= src->tsc_shift;
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return pv_tsc_khz;
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}
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void pvclock_touch_watchdogs(void)
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{
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touch_softlockup_watchdog_sync();
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clocksource_touch_watchdog();
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rcu_cpu_stall_reset();
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reset_hung_task_detector();
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}
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static atomic64_t last_value = ATOMIC64_INIT(0);
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void pvclock_resume(void)
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{
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atomic64_set(&last_value, 0);
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}
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u8 pvclock_read_flags(struct pvclock_vcpu_time_info *src)
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{
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unsigned version;
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u8 flags;
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do {
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version = pvclock_read_begin(src);
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flags = src->flags;
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} while (pvclock_read_retry(src, version));
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return flags & valid_flags;
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}
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cycle_t pvclock_clocksource_read(struct pvclock_vcpu_time_info *src)
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{
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unsigned version;
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cycle_t ret;
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u64 last;
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u8 flags;
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do {
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version = pvclock_read_begin(src);
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ret = __pvclock_read_cycles(src, rdtsc_ordered());
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flags = src->flags;
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} while (pvclock_read_retry(src, version));
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if (unlikely((flags & PVCLOCK_GUEST_STOPPED) != 0)) {
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src->flags &= ~PVCLOCK_GUEST_STOPPED;
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pvclock_touch_watchdogs();
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}
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if ((valid_flags & PVCLOCK_TSC_STABLE_BIT) &&
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(flags & PVCLOCK_TSC_STABLE_BIT))
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return ret;
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/*
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* Assumption here is that last_value, a global accumulator, always goes
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* forward. If we are less than that, we should not be much smaller.
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* We assume there is an error marging we're inside, and then the correction
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* does not sacrifice accuracy.
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*
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* For reads: global may have changed between test and return,
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* but this means someone else updated poked the clock at a later time.
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* We just need to make sure we are not seeing a backwards event.
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*
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* For updates: last_value = ret is not enough, since two vcpus could be
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* updating at the same time, and one of them could be slightly behind,
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* making the assumption that last_value always go forward fail to hold.
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*/
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last = atomic64_read(&last_value);
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do {
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if (ret < last)
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return last;
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last = atomic64_cmpxchg(&last_value, last, ret);
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} while (unlikely(last != ret));
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return ret;
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}
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void pvclock_read_wallclock(struct pvclock_wall_clock *wall_clock,
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struct pvclock_vcpu_time_info *vcpu_time,
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struct timespec *ts)
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{
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u32 version;
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u64 delta;
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struct timespec now;
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/* get wallclock at system boot */
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do {
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version = wall_clock->version;
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rmb(); /* fetch version before time */
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now.tv_sec = wall_clock->sec;
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now.tv_nsec = wall_clock->nsec;
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rmb(); /* fetch time before checking version */
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} while ((wall_clock->version & 1) || (version != wall_clock->version));
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delta = pvclock_clocksource_read(vcpu_time); /* time since system boot */
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delta += now.tv_sec * (u64)NSEC_PER_SEC + now.tv_nsec;
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now.tv_nsec = do_div(delta, NSEC_PER_SEC);
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now.tv_sec = delta;
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set_normalized_timespec(ts, now.tv_sec, now.tv_nsec);
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}
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