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 <linux/notifier.h> 21 #include <linux/sched.h> 22 #include <linux/gfp.h> 23 #include <linux/bootmem.h> 24 #include <linux/nmi.h> 25 26 #include <asm/fixmap.h> 27 #include <asm/pvclock.h> 28 29 static u8 valid_flags __read_mostly = 0; 30 31 void pvclock_set_flags(u8 flags) 32 { 33 valid_flags = flags; 34 } 35 36 unsigned long pvclock_tsc_khz(struct pvclock_vcpu_time_info *src) 37 { 38 u64 pv_tsc_khz = 1000000ULL << 32; 39 40 do_div(pv_tsc_khz, src->tsc_to_system_mul); 41 if (src->tsc_shift < 0) 42 pv_tsc_khz <<= -src->tsc_shift; 43 else 44 pv_tsc_khz >>= src->tsc_shift; 45 return pv_tsc_khz; 46 } 47 48 void pvclock_touch_watchdogs(void) 49 { 50 touch_softlockup_watchdog_sync(); 51 clocksource_touch_watchdog(); 52 rcu_cpu_stall_reset(); 53 reset_hung_task_detector(); 54 } 55 56 static atomic64_t last_value = ATOMIC64_INIT(0); 57 58 void pvclock_resume(void) 59 { 60 atomic64_set(&last_value, 0); 61 } 62 63 u8 pvclock_read_flags(struct pvclock_vcpu_time_info *src) 64 { 65 unsigned version; 66 u8 flags; 67 68 do { 69 version = pvclock_read_begin(src); 70 flags = src->flags; 71 } while (pvclock_read_retry(src, version)); 72 73 return flags & valid_flags; 74 } 75 76 u64 pvclock_clocksource_read(struct pvclock_vcpu_time_info *src) 77 { 78 unsigned version; 79 u64 ret; 80 u64 last; 81 u8 flags; 82 83 do { 84 version = pvclock_read_begin(src); 85 ret = __pvclock_read_cycles(src, rdtsc_ordered()); 86 flags = src->flags; 87 } while (pvclock_read_retry(src, version)); 88 89 if (unlikely((flags & PVCLOCK_GUEST_STOPPED) != 0)) { 90 src->flags &= ~PVCLOCK_GUEST_STOPPED; 91 pvclock_touch_watchdogs(); 92 } 93 94 if ((valid_flags & PVCLOCK_TSC_STABLE_BIT) && 95 (flags & PVCLOCK_TSC_STABLE_BIT)) 96 return ret; 97 98 /* 99 * Assumption here is that last_value, a global accumulator, always goes 100 * forward. If we are less than that, we should not be much smaller. 101 * We assume there is an error marging we're inside, and then the correction 102 * does not sacrifice accuracy. 103 * 104 * For reads: global may have changed between test and return, 105 * but this means someone else updated poked the clock at a later time. 106 * We just need to make sure we are not seeing a backwards event. 107 * 108 * For updates: last_value = ret is not enough, since two vcpus could be 109 * updating at the same time, and one of them could be slightly behind, 110 * making the assumption that last_value always go forward fail to hold. 111 */ 112 last = atomic64_read(&last_value); 113 do { 114 if (ret < last) 115 return last; 116 last = atomic64_cmpxchg(&last_value, last, ret); 117 } while (unlikely(last != ret)); 118 119 return ret; 120 } 121 122 void pvclock_read_wallclock(struct pvclock_wall_clock *wall_clock, 123 struct pvclock_vcpu_time_info *vcpu_time, 124 struct timespec *ts) 125 { 126 u32 version; 127 u64 delta; 128 struct timespec now; 129 130 /* get wallclock at system boot */ 131 do { 132 version = wall_clock->version; 133 rmb(); /* fetch version before time */ 134 now.tv_sec = wall_clock->sec; 135 now.tv_nsec = wall_clock->nsec; 136 rmb(); /* fetch time before checking version */ 137 } while ((wall_clock->version & 1) || (version != wall_clock->version)); 138 139 delta = pvclock_clocksource_read(vcpu_time); /* time since system boot */ 140 delta += now.tv_sec * (u64)NSEC_PER_SEC + now.tv_nsec; 141 142 now.tv_nsec = do_div(delta, NSEC_PER_SEC); 143 now.tv_sec = delta; 144 145 set_normalized_timespec(ts, now.tv_sec, now.tv_nsec); 146 } 147