blob: 42eb3300dfc6c35630aab267e051678f1a677e59 [file] [log] [blame]
/* paravirtual clock -- common code used by kvm/xen
This program is free software; you can redistribute it and/or modify
it under the terms of the GNU General Public License as published by
the Free Software Foundation; either version 2 of the License, or
(at your option) any later version.
This program is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
GNU General Public License for more details.
You should have received a copy of the GNU General Public License
along with this program; if not, write to the Free Software
Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA
#include <linux/kernel.h>
#include <linux/percpu.h>
#include <asm/pvclock.h>
* These are perodically updated
* xen: magic shared_info page
* kvm: gpa registered via msr
* and then copied here.
struct pvclock_shadow_time {
u64 tsc_timestamp; /* TSC at last update of time vals. */
u64 system_timestamp; /* Time, in nanosecs, since boot. */
u32 tsc_to_nsec_mul;
int tsc_shift;
u32 version;
u8 flags;
static u8 valid_flags __read_mostly = 0;
void pvclock_set_flags(u8 flags)
valid_flags = flags;
static u64 pvclock_get_nsec_offset(struct pvclock_shadow_time *shadow)
u64 delta = native_read_tsc() - shadow->tsc_timestamp;
return pvclock_scale_delta(delta, shadow->tsc_to_nsec_mul,
* Reads a consistent set of time-base values from hypervisor,
* into a shadow data area.
static unsigned pvclock_get_time_values(struct pvclock_shadow_time *dst,
struct pvclock_vcpu_time_info *src)
do {
dst->version = src->version;
rmb(); /* fetch version before data */
dst->tsc_timestamp = src->tsc_timestamp;
dst->system_timestamp = src->system_time;
dst->tsc_to_nsec_mul = src->tsc_to_system_mul;
dst->tsc_shift = src->tsc_shift;
dst->flags = src->flags;
rmb(); /* test version after fetching data */
} while ((src->version & 1) || (dst->version != src->version));
return dst->version;
unsigned long pvclock_tsc_khz(struct pvclock_vcpu_time_info *src)
u64 pv_tsc_khz = 1000000ULL << 32;
do_div(pv_tsc_khz, src->tsc_to_system_mul);
if (src->tsc_shift < 0)
pv_tsc_khz <<= -src->tsc_shift;
pv_tsc_khz >>= src->tsc_shift;
return pv_tsc_khz;
static atomic64_t last_value = ATOMIC64_INIT(0);
void pvclock_resume(void)
atomic64_set(&last_value, 0);
cycle_t pvclock_clocksource_read(struct pvclock_vcpu_time_info *src)
struct pvclock_shadow_time shadow;
unsigned version;
cycle_t ret, offset;
u64 last;
do {
version = pvclock_get_time_values(&shadow, src);
offset = pvclock_get_nsec_offset(&shadow);
ret = shadow.system_timestamp + offset;
} while (version != src->version);
if ((valid_flags & PVCLOCK_TSC_STABLE_BIT) &&
(shadow.flags & PVCLOCK_TSC_STABLE_BIT))
return ret;
* Assumption here is that last_value, a global accumulator, always goes
* forward. If we are less than that, we should not be much smaller.
* We assume there is an error marging we're inside, and then the correction
* does not sacrifice accuracy.
* For reads: global may have changed between test and return,
* but this means someone else updated poked the clock at a later time.
* We just need to make sure we are not seeing a backwards event.
* For updates: last_value = ret is not enough, since two vcpus could be
* updating at the same time, and one of them could be slightly behind,
* making the assumption that last_value always go forward fail to hold.
last = atomic64_read(&last_value);
do {
if (ret < last)
return last;
last = atomic64_cmpxchg(&last_value, last, ret);
} while (unlikely(last != ret));
return ret;
void pvclock_read_wallclock(struct pvclock_wall_clock *wall_clock,
struct pvclock_vcpu_time_info *vcpu_time,
struct timespec *ts)
u32 version;
u64 delta;
struct timespec now;
/* get wallclock at system boot */
do {
version = wall_clock->version;
rmb(); /* fetch version before time */
now.tv_sec = wall_clock->sec;
now.tv_nsec = wall_clock->nsec;
rmb(); /* fetch time before checking version */
} while ((wall_clock->version & 1) || (version != wall_clock->version));
delta = pvclock_clocksource_read(vcpu_time); /* time since system boot */
delta += now.tv_sec * (u64)NSEC_PER_SEC + now.tv_nsec;
now.tv_nsec = do_div(delta, NSEC_PER_SEC);
now.tv_sec = delta;
set_normalized_timespec(ts, now.tv_sec, now.tv_nsec);