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 <asm/pvclock.h> 21 22 /* 23 * These are perodically updated 24 * xen: magic shared_info page 25 * kvm: gpa registered via msr 26 * and then copied here. 27 */ 28 struct pvclock_shadow_time { 29 u64 tsc_timestamp; /* TSC at last update of time vals. */ 30 u64 system_timestamp; /* Time, in nanosecs, since boot. */ 31 u32 tsc_to_nsec_mul; 32 int tsc_shift; 33 u32 version; 34 u8 flags; 35 }; 36 37 static u8 valid_flags __read_mostly = 0; 38 39 void pvclock_set_flags(u8 flags) 40 { 41 valid_flags = flags; 42 } 43 44 static u64 pvclock_get_nsec_offset(struct pvclock_shadow_time *shadow) 45 { 46 u64 delta = native_read_tsc() - shadow->tsc_timestamp; 47 return pvclock_scale_delta(delta, shadow->tsc_to_nsec_mul, 48 shadow->tsc_shift); 49 } 50 51 /* 52 * Reads a consistent set of time-base values from hypervisor, 53 * into a shadow data area. 54 */ 55 static unsigned pvclock_get_time_values(struct pvclock_shadow_time *dst, 56 struct pvclock_vcpu_time_info *src) 57 { 58 do { 59 dst->version = src->version; 60 rmb(); /* fetch version before data */ 61 dst->tsc_timestamp = src->tsc_timestamp; 62 dst->system_timestamp = src->system_time; 63 dst->tsc_to_nsec_mul = src->tsc_to_system_mul; 64 dst->tsc_shift = src->tsc_shift; 65 dst->flags = src->flags; 66 rmb(); /* test version after fetching data */ 67 } while ((src->version & 1) || (dst->version != src->version)); 68 69 return dst->version; 70 } 71 72 unsigned long pvclock_tsc_khz(struct pvclock_vcpu_time_info *src) 73 { 74 u64 pv_tsc_khz = 1000000ULL << 32; 75 76 do_div(pv_tsc_khz, src->tsc_to_system_mul); 77 if (src->tsc_shift < 0) 78 pv_tsc_khz <<= -src->tsc_shift; 79 else 80 pv_tsc_khz >>= src->tsc_shift; 81 return pv_tsc_khz; 82 } 83 84 static atomic64_t last_value = ATOMIC64_INIT(0); 85 86 cycle_t pvclock_clocksource_read(struct pvclock_vcpu_time_info *src) 87 { 88 struct pvclock_shadow_time shadow; 89 unsigned version; 90 cycle_t ret, offset; 91 u64 last; 92 93 do { 94 version = pvclock_get_time_values(&shadow, src); 95 barrier(); 96 offset = pvclock_get_nsec_offset(&shadow); 97 ret = shadow.system_timestamp + offset; 98 barrier(); 99 } while (version != src->version); 100 101 if ((valid_flags & PVCLOCK_TSC_STABLE_BIT) && 102 (shadow.flags & PVCLOCK_TSC_STABLE_BIT)) 103 return ret; 104 105 /* 106 * Assumption here is that last_value, a global accumulator, always goes 107 * forward. If we are less than that, we should not be much smaller. 108 * We assume there is an error marging we're inside, and then the correction 109 * does not sacrifice accuracy. 110 * 111 * For reads: global may have changed between test and return, 112 * but this means someone else updated poked the clock at a later time. 113 * We just need to make sure we are not seeing a backwards event. 114 * 115 * For updates: last_value = ret is not enough, since two vcpus could be 116 * updating at the same time, and one of them could be slightly behind, 117 * making the assumption that last_value always go forward fail to hold. 118 */ 119 last = atomic64_read(&last_value); 120 do { 121 if (ret < last) 122 return last; 123 last = atomic64_cmpxchg(&last_value, last, ret); 124 } while (unlikely(last != ret)); 125 126 return ret; 127 } 128 129 void pvclock_read_wallclock(struct pvclock_wall_clock *wall_clock, 130 struct pvclock_vcpu_time_info *vcpu_time, 131 struct timespec *ts) 132 { 133 u32 version; 134 u64 delta; 135 struct timespec now; 136 137 /* get wallclock at system boot */ 138 do { 139 version = wall_clock->version; 140 rmb(); /* fetch version before time */ 141 now.tv_sec = wall_clock->sec; 142 now.tv_nsec = wall_clock->nsec; 143 rmb(); /* fetch time before checking version */ 144 } while ((wall_clock->version & 1) || (version != wall_clock->version)); 145 146 delta = pvclock_clocksource_read(vcpu_time); /* time since system boot */ 147 delta += now.tv_sec * (u64)NSEC_PER_SEC + now.tv_nsec; 148 149 now.tv_nsec = do_div(delta, NSEC_PER_SEC); 150 now.tv_sec = delta; 151 152 set_normalized_timespec(ts, now.tv_sec, now.tv_nsec); 153 } 154