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 }; 35 36 /* 37 * Scale a 64-bit delta by scaling and multiplying by a 32-bit fraction, 38 * yielding a 64-bit result. 39 */ 40 static inline u64 scale_delta(u64 delta, u32 mul_frac, int shift) 41 { 42 u64 product; 43 #ifdef __i386__ 44 u32 tmp1, tmp2; 45 #endif 46 47 if (shift < 0) 48 delta >>= -shift; 49 else 50 delta <<= shift; 51 52 #ifdef __i386__ 53 __asm__ ( 54 "mul %5 ; " 55 "mov %4,%%eax ; " 56 "mov %%edx,%4 ; " 57 "mul %5 ; " 58 "xor %5,%5 ; " 59 "add %4,%%eax ; " 60 "adc %5,%%edx ; " 61 : "=A" (product), "=r" (tmp1), "=r" (tmp2) 62 : "a" ((u32)delta), "1" ((u32)(delta >> 32)), "2" (mul_frac) ); 63 #elif __x86_64__ 64 __asm__ ( 65 "mul %%rdx ; shrd $32,%%rdx,%%rax" 66 : "=a" (product) : "0" (delta), "d" ((u64)mul_frac) ); 67 #else 68 #error implement me! 69 #endif 70 71 return product; 72 } 73 74 static u64 pvclock_get_nsec_offset(struct pvclock_shadow_time *shadow) 75 { 76 u64 delta = native_read_tsc() - shadow->tsc_timestamp; 77 return scale_delta(delta, shadow->tsc_to_nsec_mul, shadow->tsc_shift); 78 } 79 80 /* 81 * Reads a consistent set of time-base values from hypervisor, 82 * into a shadow data area. 83 */ 84 static unsigned pvclock_get_time_values(struct pvclock_shadow_time *dst, 85 struct pvclock_vcpu_time_info *src) 86 { 87 do { 88 dst->version = src->version; 89 rmb(); /* fetch version before data */ 90 dst->tsc_timestamp = src->tsc_timestamp; 91 dst->system_timestamp = src->system_time; 92 dst->tsc_to_nsec_mul = src->tsc_to_system_mul; 93 dst->tsc_shift = src->tsc_shift; 94 rmb(); /* test version after fetching data */ 95 } while ((src->version & 1) || (dst->version != src->version)); 96 97 return dst->version; 98 } 99 100 cycle_t pvclock_clocksource_read(struct pvclock_vcpu_time_info *src) 101 { 102 struct pvclock_shadow_time shadow; 103 unsigned version; 104 cycle_t ret, offset; 105 106 do { 107 version = pvclock_get_time_values(&shadow, src); 108 barrier(); 109 offset = pvclock_get_nsec_offset(&shadow); 110 ret = shadow.system_timestamp + offset; 111 barrier(); 112 } while (version != src->version); 113 114 return ret; 115 } 116 117 void pvclock_read_wallclock(struct pvclock_wall_clock *wall_clock, 118 struct pvclock_vcpu_time_info *vcpu_time, 119 struct timespec *ts) 120 { 121 u32 version; 122 u64 delta; 123 struct timespec now; 124 125 /* get wallclock at system boot */ 126 do { 127 version = wall_clock->version; 128 rmb(); /* fetch version before time */ 129 now.tv_sec = wall_clock->sec; 130 now.tv_nsec = wall_clock->nsec; 131 rmb(); /* fetch time before checking version */ 132 } while ((wall_clock->version & 1) || (version != wall_clock->version)); 133 134 delta = pvclock_clocksource_read(vcpu_time); /* time since system boot */ 135 delta += now.tv_sec * (u64)NSEC_PER_SEC + now.tv_nsec; 136 137 now.tv_nsec = do_div(delta, NSEC_PER_SEC); 138 now.tv_sec = delta; 139 140 set_normalized_timespec(ts, now.tv_sec, now.tv_nsec); 141 } 142