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
19static u8 valid_flags __read_mostly = 0;
20static struct pvclock_vsyscall_time_info *pvti_cpu0_va __read_mostly;
21
22void pvclock_set_flags(u8 flags)
23{
24	valid_flags = flags;
25}
26
27unsigned 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
39void 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
47static atomic64_t last_value = ATOMIC64_INIT(0);
48
49void pvclock_resume(void)
50{
51	atomic64_set(&last_value, 0);
52}
53
54u8 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
67static __always_inline
68u64 __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
113u64 pvclock_clocksource_read(struct pvclock_vcpu_time_info *src)
114{
115	return __pvclock_clocksource_read(src, true);
116}
117
118noinstr u64 pvclock_clocksource_read_nowd(struct pvclock_vcpu_time_info *src)
119{
120	return __pvclock_clocksource_read(src, false);
121}
122
123void 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
156void 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
162struct pvclock_vsyscall_time_info *pvclock_get_pvti_cpu0_va(void)
163{
164	return pvti_cpu0_va;
165}
166EXPORT_SYMBOL_GPL(pvclock_get_pvti_cpu0_va);
167