/* 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 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the 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, shadow->tsc_shift); } /* * 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; else 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); barrier(); offset = pvclock_get_nsec_offset(&shadow); ret = shadow.system_timestamp + offset; barrier(); } 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); }