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
pvclock_set_flags(u8 flags)39 void pvclock_set_flags(u8 flags)
40 {
41 valid_flags = flags;
42 }
43
pvclock_get_nsec_offset(struct pvclock_shadow_time * shadow)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 */
pvclock_get_time_values(struct pvclock_shadow_time * dst,struct pvclock_vcpu_time_info * src)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
pvclock_tsc_khz(struct pvclock_vcpu_time_info * src)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
pvclock_resume(void)86 void pvclock_resume(void)
87 {
88 atomic64_set(&last_value, 0);
89 }
90
pvclock_clocksource_read(struct pvclock_vcpu_time_info * src)91 cycle_t pvclock_clocksource_read(struct pvclock_vcpu_time_info *src)
92 {
93 struct pvclock_shadow_time shadow;
94 unsigned version;
95 cycle_t ret, offset;
96 u64 last;
97
98 do {
99 version = pvclock_get_time_values(&shadow, src);
100 barrier();
101 offset = pvclock_get_nsec_offset(&shadow);
102 ret = shadow.system_timestamp + offset;
103 barrier();
104 } while (version != src->version);
105
106 if ((valid_flags & PVCLOCK_TSC_STABLE_BIT) &&
107 (shadow.flags & PVCLOCK_TSC_STABLE_BIT))
108 return ret;
109
110 /*
111 * Assumption here is that last_value, a global accumulator, always goes
112 * forward. If we are less than that, we should not be much smaller.
113 * We assume there is an error marging we're inside, and then the correction
114 * does not sacrifice accuracy.
115 *
116 * For reads: global may have changed between test and return,
117 * but this means someone else updated poked the clock at a later time.
118 * We just need to make sure we are not seeing a backwards event.
119 *
120 * For updates: last_value = ret is not enough, since two vcpus could be
121 * updating at the same time, and one of them could be slightly behind,
122 * making the assumption that last_value always go forward fail to hold.
123 */
124 last = atomic64_read(&last_value);
125 do {
126 if (ret < last)
127 return last;
128 last = atomic64_cmpxchg(&last_value, last, ret);
129 } while (unlikely(last != ret));
130
131 return ret;
132 }
133
pvclock_read_wallclock(struct pvclock_wall_clock * wall_clock,struct pvclock_vcpu_time_info * vcpu_time,struct timespec * ts)134 void pvclock_read_wallclock(struct pvclock_wall_clock *wall_clock,
135 struct pvclock_vcpu_time_info *vcpu_time,
136 struct timespec *ts)
137 {
138 u32 version;
139 u64 delta;
140 struct timespec now;
141
142 /* get wallclock at system boot */
143 do {
144 version = wall_clock->version;
145 rmb(); /* fetch version before time */
146 now.tv_sec = wall_clock->sec;
147 now.tv_nsec = wall_clock->nsec;
148 rmb(); /* fetch time before checking version */
149 } while ((wall_clock->version & 1) || (version != wall_clock->version));
150
151 delta = pvclock_clocksource_read(vcpu_time); /* time since system boot */
152 delta += now.tv_sec * (u64)NSEC_PER_SEC + now.tv_nsec;
153
154 now.tv_nsec = do_div(delta, NSEC_PER_SEC);
155 now.tv_sec = delta;
156
157 set_normalized_timespec(ts, now.tv_sec, now.tv_nsec);
158 }
159