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 <asm/fixmap.h> 25 #include <asm/pvclock.h> 26 27 static u8 valid_flags __read_mostly = 0; 28 29 void pvclock_set_flags(u8 flags) 30 { 31 valid_flags = flags; 32 } 33 34 unsigned long pvclock_tsc_khz(struct pvclock_vcpu_time_info *src) 35 { 36 u64 pv_tsc_khz = 1000000ULL << 32; 37 38 do_div(pv_tsc_khz, src->tsc_to_system_mul); 39 if (src->tsc_shift < 0) 40 pv_tsc_khz <<= -src->tsc_shift; 41 else 42 pv_tsc_khz >>= src->tsc_shift; 43 return pv_tsc_khz; 44 } 45 46 static atomic64_t last_value = ATOMIC64_INIT(0); 47 48 void pvclock_resume(void) 49 { 50 atomic64_set(&last_value, 0); 51 } 52 53 u8 pvclock_read_flags(struct pvclock_vcpu_time_info *src) 54 { 55 unsigned version; 56 cycle_t ret; 57 u8 flags; 58 59 do { 60 version = __pvclock_read_cycles(src, &ret, &flags); 61 } while ((src->version & 1) || version != src->version); 62 63 return flags & valid_flags; 64 } 65 66 cycle_t pvclock_clocksource_read(struct pvclock_vcpu_time_info *src) 67 { 68 unsigned version; 69 cycle_t ret; 70 u64 last; 71 u8 flags; 72 73 do { 74 version = __pvclock_read_cycles(src, &ret, &flags); 75 } while ((src->version & 1) || version != src->version); 76 77 if ((valid_flags & PVCLOCK_TSC_STABLE_BIT) && 78 (flags & PVCLOCK_TSC_STABLE_BIT)) 79 return ret; 80 81 /* 82 * Assumption here is that last_value, a global accumulator, always goes 83 * forward. If we are less than that, we should not be much smaller. 84 * We assume there is an error marging we're inside, and then the correction 85 * does not sacrifice accuracy. 86 * 87 * For reads: global may have changed between test and return, 88 * but this means someone else updated poked the clock at a later time. 89 * We just need to make sure we are not seeing a backwards event. 90 * 91 * For updates: last_value = ret is not enough, since two vcpus could be 92 * updating at the same time, and one of them could be slightly behind, 93 * making the assumption that last_value always go forward fail to hold. 94 */ 95 last = atomic64_read(&last_value); 96 do { 97 if (ret < last) 98 return last; 99 last = atomic64_cmpxchg(&last_value, last, ret); 100 } while (unlikely(last != ret)); 101 102 return ret; 103 } 104 105 void pvclock_read_wallclock(struct pvclock_wall_clock *wall_clock, 106 struct pvclock_vcpu_time_info *vcpu_time, 107 struct timespec *ts) 108 { 109 u32 version; 110 u64 delta; 111 struct timespec now; 112 113 /* get wallclock at system boot */ 114 do { 115 version = wall_clock->version; 116 rmb(); /* fetch version before time */ 117 now.tv_sec = wall_clock->sec; 118 now.tv_nsec = wall_clock->nsec; 119 rmb(); /* fetch time before checking version */ 120 } while ((wall_clock->version & 1) || (version != wall_clock->version)); 121 122 delta = pvclock_clocksource_read(vcpu_time); /* time since system boot */ 123 delta += now.tv_sec * (u64)NSEC_PER_SEC + now.tv_nsec; 124 125 now.tv_nsec = do_div(delta, NSEC_PER_SEC); 126 now.tv_sec = delta; 127 128 set_normalized_timespec(ts, now.tv_sec, now.tv_nsec); 129 } 130 131 #ifdef CONFIG_X86_64 132 /* 133 * Initialize the generic pvclock vsyscall state. This will allocate 134 * a/some page(s) for the per-vcpu pvclock information, set up a 135 * fixmap mapping for the page(s) 136 */ 137 138 int __init pvclock_init_vsyscall(struct pvclock_vsyscall_time_info *i, 139 int size) 140 { 141 int idx; 142 143 WARN_ON (size != PVCLOCK_VSYSCALL_NR_PAGES*PAGE_SIZE); 144 145 for (idx = 0; idx <= (PVCLOCK_FIXMAP_END-PVCLOCK_FIXMAP_BEGIN); idx++) { 146 __set_fixmap(PVCLOCK_FIXMAP_BEGIN + idx, 147 __pa(i) + (idx*PAGE_SIZE), 148 PAGE_KERNEL_VVAR); 149 } 150 151 return 0; 152 } 153 #endif 154