1 // SPDX-License-Identifier: GPL-2.0-or-later
2 /* paravirtual clock -- common code used by kvm/xen
3
4 */
5
6 #include <linux/clocksource.h>
7 #include <linux/kernel.h>
8 #include <linux/percpu.h>
9 #include <linux/notifier.h>
10 #include <linux/sched.h>
11 #include <linux/gfp.h>
12 #include <linux/memblock.h>
13 #include <linux/nmi.h>
14
15 #include <asm/fixmap.h>
16 #include <asm/pvclock.h>
17 #include <asm/vgtod.h>
18
19 static u8 valid_flags __read_mostly = 0;
20 static struct pvclock_vsyscall_time_info *pvti_cpu0_va __read_mostly;
21
22 void pvclock_set_flags(u8 flags)
23 {
24 valid_flags = flags;
25 }
26
27 unsigned long pvclock_tsc_khz(struct pvclock_vcpu_time_info *src)
28 {
29 u64 pv_tsc_khz = 1000000ULL << 32;
30
31 do_div(pv_tsc_khz, src->tsc_to_system_mul);
32 if (src->tsc_shift < 0)
33 pv_tsc_khz <<= -src->tsc_shift;
34 else
35 pv_tsc_khz >>= src->tsc_shift;
36 return pv_tsc_khz;
37 }
38
39 void pvclock_touch_watchdogs(void)
40 {
41 touch_softlockup_watchdog_sync();
42 clocksource_touch_watchdog();
43 rcu_cpu_stall_reset();
44 reset_hung_task_detector();
45 }
46
47 static atomic64_t last_value = ATOMIC64_INIT(0);
48
49 void pvclock_resume(void)
50 {
51 atomic64_set(&last_value, 0);
52 }
53
54 u8 pvclock_read_flags(struct pvclock_vcpu_time_info *src)
55 {
56 unsigned version;
57 u8 flags;
58
59 do {
60 version = pvclock_read_begin(src);
61 flags = src->flags;
62 } while (pvclock_read_retry(src, version));
63
64 return flags & valid_flags;
65 }
66
67 static __always_inline
68 u64 __pvclock_clocksource_read(struct pvclock_vcpu_time_info *src, bool dowd)
69 {
70 unsigned version;
71 u64 ret;
72 u64 last;
73 u8 flags;
74
75 do {
76 version = pvclock_read_begin(src);
77 ret = __pvclock_read_cycles(src, rdtsc_ordered());
78 flags = src->flags;
79 } while (pvclock_read_retry(src, version));
80
81 if (dowd && unlikely((flags & PVCLOCK_GUEST_STOPPED) != 0)) {
82 src->flags &= ~PVCLOCK_GUEST_STOPPED;
83 pvclock_touch_watchdogs();
84 }
85
86 if ((valid_flags & PVCLOCK_TSC_STABLE_BIT) &&
87 (flags & PVCLOCK_TSC_STABLE_BIT))
88 return ret;
89
90 /*
91 * Assumption here is that last_value, a global accumulator, always goes
92 * forward. If we are less than that, we should not be much smaller.
93 * We assume there is an error margin we're inside, and then the correction
94 * does not sacrifice accuracy.
95 *
96 * For reads: global may have changed between test and return,
97 * but this means someone else updated poked the clock at a later time.
98 * We just need to make sure we are not seeing a backwards event.
99 *
100 * For updates: last_value = ret is not enough, since two vcpus could be
101 * updating at the same time, and one of them could be slightly behind,
102 * making the assumption that last_value always go forward fail to hold.
103 */
104 last = raw_atomic64_read(&last_value);
105 do {
106 if (ret <= last)
107 return last;
108 } while (!raw_atomic64_try_cmpxchg(&last_value, &last, ret));
109
110 return ret;
111 }
112
113 u64 pvclock_clocksource_read(struct pvclock_vcpu_time_info *src)
114 {
115 return __pvclock_clocksource_read(src, true);
116 }
117
118 noinstr u64 pvclock_clocksource_read_nowd(struct pvclock_vcpu_time_info *src)
119 {
120 return __pvclock_clocksource_read(src, false);
121 }
122
123 void pvclock_read_wallclock(struct pvclock_wall_clock *wall_clock,
124 struct pvclock_vcpu_time_info *vcpu_time,
125 struct timespec64 *ts)
126 {
127 u32 version;
128 u64 delta;
129 struct timespec64 now;
130
131 /* get wallclock at system boot */
132 do {
133 version = wall_clock->version;
134 rmb(); /* fetch version before time */
135 /*
136 * Note: wall_clock->sec is a u32 value, so it can
137 * only store dates between 1970 and 2106. To allow
138 * times beyond that, we need to create a new hypercall
139 * interface with an extended pvclock_wall_clock structure
140 * like ARM has.
141 */
142 now.tv_sec = wall_clock->sec;
143 now.tv_nsec = wall_clock->nsec;
144 rmb(); /* fetch time before checking version */
145 } while ((wall_clock->version & 1) || (version != wall_clock->version));
146
147 delta = pvclock_clocksource_read(vcpu_time); /* time since system boot */
148 delta += now.tv_sec * NSEC_PER_SEC + now.tv_nsec;
149
150 now.tv_nsec = do_div(delta, NSEC_PER_SEC);
151 now.tv_sec = delta;
152
153 set_normalized_timespec64(ts, now.tv_sec, now.tv_nsec);
154 }
155
156 void pvclock_set_pvti_cpu0_va(struct pvclock_vsyscall_time_info *pvti)
157 {
158 WARN_ON(vclock_was_used(VDSO_CLOCKMODE_PVCLOCK));
159 pvti_cpu0_va = pvti;
160 }
161
162 struct pvclock_vsyscall_time_info *pvclock_get_pvti_cpu0_va(void)
163 {
164 return pvti_cpu0_va;
165 }
166 EXPORT_SYMBOL_GPL(pvclock_get_pvti_cpu0_va);
167
Linux® is a registered trademark of Linus Torvalds in the United States and other countries.
TOMOYO® is a registered trademark of NTT DATA CORPORATION.