xref: /linux/arch/x86/xen/time.c (revision a1ff5a7d78a036d6c2178ee5acd6ba4946243800)
1 // SPDX-License-Identifier: GPL-2.0
2 /*
3  * Xen time implementation.
4  *
5  * This is implemented in terms of a clocksource driver which uses
6  * the hypervisor clock as a nanosecond timebase, and a clockevent
7  * driver which uses the hypervisor's timer mechanism.
8  *
9  * Jeremy Fitzhardinge <jeremy@xensource.com>, XenSource Inc, 2007
10  */
11 #include <linux/kernel.h>
12 #include <linux/interrupt.h>
13 #include <linux/clocksource.h>
14 #include <linux/clockchips.h>
15 #include <linux/gfp.h>
16 #include <linux/slab.h>
17 #include <linux/pvclock_gtod.h>
18 #include <linux/timekeeper_internal.h>
19 
20 #include <asm/pvclock.h>
21 #include <asm/xen/hypervisor.h>
22 #include <asm/xen/hypercall.h>
23 #include <asm/xen/cpuid.h>
24 
25 #include <xen/events.h>
26 #include <xen/features.h>
27 #include <xen/interface/xen.h>
28 #include <xen/interface/vcpu.h>
29 
30 #include "xen-ops.h"
31 
32 /* Minimum amount of time until next clock event fires */
33 #define TIMER_SLOP	1
34 
35 static u64 xen_sched_clock_offset __read_mostly;
36 
37 /* Get the TSC speed from Xen */
xen_tsc_khz(void)38 static unsigned long xen_tsc_khz(void)
39 {
40 	struct pvclock_vcpu_time_info *info =
41 		&HYPERVISOR_shared_info->vcpu_info[0].time;
42 
43 	setup_force_cpu_cap(X86_FEATURE_TSC_KNOWN_FREQ);
44 	return pvclock_tsc_khz(info);
45 }
46 
xen_clocksource_read(void)47 static u64 xen_clocksource_read(void)
48 {
49         struct pvclock_vcpu_time_info *src;
50 	u64 ret;
51 
52 	preempt_disable_notrace();
53 	src = &__this_cpu_read(xen_vcpu)->time;
54 	ret = pvclock_clocksource_read(src);
55 	preempt_enable_notrace();
56 	return ret;
57 }
58 
xen_clocksource_get_cycles(struct clocksource * cs)59 static u64 xen_clocksource_get_cycles(struct clocksource *cs)
60 {
61 	return xen_clocksource_read();
62 }
63 
xen_sched_clock(void)64 static noinstr u64 xen_sched_clock(void)
65 {
66         struct pvclock_vcpu_time_info *src;
67 	u64 ret;
68 
69 	src = &__this_cpu_read(xen_vcpu)->time;
70 	ret = pvclock_clocksource_read_nowd(src);
71 	ret -= xen_sched_clock_offset;
72 
73 	return ret;
74 }
75 
xen_read_wallclock(struct timespec64 * ts)76 static void xen_read_wallclock(struct timespec64 *ts)
77 {
78 	struct shared_info *s = HYPERVISOR_shared_info;
79 	struct pvclock_wall_clock *wall_clock = &(s->wc);
80         struct pvclock_vcpu_time_info *vcpu_time;
81 
82 	vcpu_time = &get_cpu_var(xen_vcpu)->time;
83 	pvclock_read_wallclock(wall_clock, vcpu_time, ts);
84 	put_cpu_var(xen_vcpu);
85 }
86 
xen_get_wallclock(struct timespec64 * now)87 static void xen_get_wallclock(struct timespec64 *now)
88 {
89 	xen_read_wallclock(now);
90 }
91 
xen_set_wallclock(const struct timespec64 * now)92 static int xen_set_wallclock(const struct timespec64 *now)
93 {
94 	return -ENODEV;
95 }
96 
xen_pvclock_gtod_notify(struct notifier_block * nb,unsigned long was_set,void * priv)97 static int xen_pvclock_gtod_notify(struct notifier_block *nb,
98 				   unsigned long was_set, void *priv)
99 {
100 	/* Protected by the calling core code serialization */
101 	static struct timespec64 next_sync;
102 
103 	struct xen_platform_op op;
104 	struct timespec64 now;
105 	struct timekeeper *tk = priv;
106 	static bool settime64_supported = true;
107 	int ret;
108 
109 	now.tv_sec = tk->xtime_sec;
110 	now.tv_nsec = (long)(tk->tkr_mono.xtime_nsec >> tk->tkr_mono.shift);
111 
112 	/*
113 	 * We only take the expensive HV call when the clock was set
114 	 * or when the 11 minutes RTC synchronization time elapsed.
115 	 */
116 	if (!was_set && timespec64_compare(&now, &next_sync) < 0)
117 		return NOTIFY_OK;
118 
119 again:
120 	if (settime64_supported) {
121 		op.cmd = XENPF_settime64;
122 		op.u.settime64.mbz = 0;
123 		op.u.settime64.secs = now.tv_sec;
124 		op.u.settime64.nsecs = now.tv_nsec;
125 		op.u.settime64.system_time = xen_clocksource_read();
126 	} else {
127 		op.cmd = XENPF_settime32;
128 		op.u.settime32.secs = now.tv_sec;
129 		op.u.settime32.nsecs = now.tv_nsec;
130 		op.u.settime32.system_time = xen_clocksource_read();
131 	}
132 
133 	ret = HYPERVISOR_platform_op(&op);
134 
135 	if (ret == -ENOSYS && settime64_supported) {
136 		settime64_supported = false;
137 		goto again;
138 	}
139 	if (ret < 0)
140 		return NOTIFY_BAD;
141 
142 	/*
143 	 * Move the next drift compensation time 11 minutes
144 	 * ahead. That's emulating the sync_cmos_clock() update for
145 	 * the hardware RTC.
146 	 */
147 	next_sync = now;
148 	next_sync.tv_sec += 11 * 60;
149 
150 	return NOTIFY_OK;
151 }
152 
153 static struct notifier_block xen_pvclock_gtod_notifier = {
154 	.notifier_call = xen_pvclock_gtod_notify,
155 };
156 
xen_cs_enable(struct clocksource * cs)157 static int xen_cs_enable(struct clocksource *cs)
158 {
159 	vclocks_set_used(VDSO_CLOCKMODE_PVCLOCK);
160 	return 0;
161 }
162 
163 static struct clocksource xen_clocksource __read_mostly = {
164 	.name	= "xen",
165 	.rating	= 400,
166 	.read	= xen_clocksource_get_cycles,
167 	.mask	= CLOCKSOURCE_MASK(64),
168 	.flags	= CLOCK_SOURCE_IS_CONTINUOUS,
169 	.enable = xen_cs_enable,
170 };
171 
172 /*
173    Xen clockevent implementation
174 
175    Xen has two clockevent implementations:
176 
177    The old timer_op one works with all released versions of Xen prior
178    to version 3.0.4.  This version of the hypervisor provides a
179    single-shot timer with nanosecond resolution.  However, sharing the
180    same event channel is a 100Hz tick which is delivered while the
181    vcpu is running.  We don't care about or use this tick, but it will
182    cause the core time code to think the timer fired too soon, and
183    will end up resetting it each time.  It could be filtered, but
184    doing so has complications when the ktime clocksource is not yet
185    the xen clocksource (ie, at boot time).
186 
187    The new vcpu_op-based timer interface allows the tick timer period
188    to be changed or turned off.  The tick timer is not useful as a
189    periodic timer because events are only delivered to running vcpus.
190    The one-shot timer can report when a timeout is in the past, so
191    set_next_event is capable of returning -ETIME when appropriate.
192    This interface is used when available.
193 */
194 
195 
196 /*
197   Get a hypervisor absolute time.  In theory we could maintain an
198   offset between the kernel's time and the hypervisor's time, and
199   apply that to a kernel's absolute timeout.  Unfortunately the
200   hypervisor and kernel times can drift even if the kernel is using
201   the Xen clocksource, because ntp can warp the kernel's clocksource.
202 */
get_abs_timeout(unsigned long delta)203 static s64 get_abs_timeout(unsigned long delta)
204 {
205 	return xen_clocksource_read() + delta;
206 }
207 
xen_timerop_shutdown(struct clock_event_device * evt)208 static int xen_timerop_shutdown(struct clock_event_device *evt)
209 {
210 	/* cancel timeout */
211 	HYPERVISOR_set_timer_op(0);
212 
213 	return 0;
214 }
215 
xen_timerop_set_next_event(unsigned long delta,struct clock_event_device * evt)216 static int xen_timerop_set_next_event(unsigned long delta,
217 				      struct clock_event_device *evt)
218 {
219 	WARN_ON(!clockevent_state_oneshot(evt));
220 
221 	if (HYPERVISOR_set_timer_op(get_abs_timeout(delta)) < 0)
222 		BUG();
223 
224 	/* We may have missed the deadline, but there's no real way of
225 	   knowing for sure.  If the event was in the past, then we'll
226 	   get an immediate interrupt. */
227 
228 	return 0;
229 }
230 
231 static struct clock_event_device xen_timerop_clockevent __ro_after_init = {
232 	.name			= "xen",
233 	.features		= CLOCK_EVT_FEAT_ONESHOT,
234 
235 	.max_delta_ns		= 0xffffffff,
236 	.max_delta_ticks	= 0xffffffff,
237 	.min_delta_ns		= TIMER_SLOP,
238 	.min_delta_ticks	= TIMER_SLOP,
239 
240 	.mult			= 1,
241 	.shift			= 0,
242 	.rating			= 500,
243 
244 	.set_state_shutdown	= xen_timerop_shutdown,
245 	.set_next_event		= xen_timerop_set_next_event,
246 };
247 
xen_vcpuop_shutdown(struct clock_event_device * evt)248 static int xen_vcpuop_shutdown(struct clock_event_device *evt)
249 {
250 	int cpu = smp_processor_id();
251 
252 	if (HYPERVISOR_vcpu_op(VCPUOP_stop_singleshot_timer, xen_vcpu_nr(cpu),
253 			       NULL) ||
254 	    HYPERVISOR_vcpu_op(VCPUOP_stop_periodic_timer, xen_vcpu_nr(cpu),
255 			       NULL))
256 		BUG();
257 
258 	return 0;
259 }
260 
xen_vcpuop_set_oneshot(struct clock_event_device * evt)261 static int xen_vcpuop_set_oneshot(struct clock_event_device *evt)
262 {
263 	int cpu = smp_processor_id();
264 
265 	if (HYPERVISOR_vcpu_op(VCPUOP_stop_periodic_timer, xen_vcpu_nr(cpu),
266 			       NULL))
267 		BUG();
268 
269 	return 0;
270 }
271 
xen_vcpuop_set_next_event(unsigned long delta,struct clock_event_device * evt)272 static int xen_vcpuop_set_next_event(unsigned long delta,
273 				     struct clock_event_device *evt)
274 {
275 	int cpu = smp_processor_id();
276 	struct vcpu_set_singleshot_timer single;
277 	int ret;
278 
279 	WARN_ON(!clockevent_state_oneshot(evt));
280 
281 	single.timeout_abs_ns = get_abs_timeout(delta);
282 	/* Get an event anyway, even if the timeout is already expired */
283 	single.flags = 0;
284 
285 	ret = HYPERVISOR_vcpu_op(VCPUOP_set_singleshot_timer, xen_vcpu_nr(cpu),
286 				 &single);
287 	BUG_ON(ret != 0);
288 
289 	return ret;
290 }
291 
292 static struct clock_event_device xen_vcpuop_clockevent __ro_after_init = {
293 	.name = "xen",
294 	.features = CLOCK_EVT_FEAT_ONESHOT,
295 
296 	.max_delta_ns = 0xffffffff,
297 	.max_delta_ticks = 0xffffffff,
298 	.min_delta_ns = TIMER_SLOP,
299 	.min_delta_ticks = TIMER_SLOP,
300 
301 	.mult = 1,
302 	.shift = 0,
303 	.rating = 500,
304 
305 	.set_state_shutdown = xen_vcpuop_shutdown,
306 	.set_state_oneshot = xen_vcpuop_set_oneshot,
307 	.set_next_event = xen_vcpuop_set_next_event,
308 };
309 
310 static const struct clock_event_device *xen_clockevent =
311 	&xen_timerop_clockevent;
312 
313 struct xen_clock_event_device {
314 	struct clock_event_device evt;
315 	char name[16];
316 };
317 static DEFINE_PER_CPU(struct xen_clock_event_device, xen_clock_events) = { .evt.irq = -1 };
318 
xen_timer_interrupt(int irq,void * dev_id)319 static irqreturn_t xen_timer_interrupt(int irq, void *dev_id)
320 {
321 	struct clock_event_device *evt = this_cpu_ptr(&xen_clock_events.evt);
322 	irqreturn_t ret;
323 
324 	ret = IRQ_NONE;
325 	if (evt->event_handler) {
326 		evt->event_handler(evt);
327 		ret = IRQ_HANDLED;
328 	}
329 
330 	return ret;
331 }
332 
xen_teardown_timer(int cpu)333 void xen_teardown_timer(int cpu)
334 {
335 	struct clock_event_device *evt;
336 	evt = &per_cpu(xen_clock_events, cpu).evt;
337 
338 	if (evt->irq >= 0) {
339 		unbind_from_irqhandler(evt->irq, NULL);
340 		evt->irq = -1;
341 	}
342 }
343 
xen_setup_timer(int cpu)344 void xen_setup_timer(int cpu)
345 {
346 	struct xen_clock_event_device *xevt = &per_cpu(xen_clock_events, cpu);
347 	struct clock_event_device *evt = &xevt->evt;
348 	int irq;
349 
350 	WARN(evt->irq >= 0, "IRQ%d for CPU%d is already allocated\n", evt->irq, cpu);
351 	if (evt->irq >= 0)
352 		xen_teardown_timer(cpu);
353 
354 	printk(KERN_INFO "installing Xen timer for CPU %d\n", cpu);
355 
356 	snprintf(xevt->name, sizeof(xevt->name), "timer%d", cpu);
357 
358 	irq = bind_virq_to_irqhandler(VIRQ_TIMER, cpu, xen_timer_interrupt,
359 				      IRQF_PERCPU|IRQF_NOBALANCING|IRQF_TIMER|
360 				      IRQF_FORCE_RESUME|IRQF_EARLY_RESUME,
361 				      xevt->name, NULL);
362 	(void)xen_set_irq_priority(irq, XEN_IRQ_PRIORITY_MAX);
363 
364 	memcpy(evt, xen_clockevent, sizeof(*evt));
365 
366 	evt->cpumask = cpumask_of(cpu);
367 	evt->irq = irq;
368 }
369 
370 
xen_setup_cpu_clockevents(void)371 void xen_setup_cpu_clockevents(void)
372 {
373 	clockevents_register_device(this_cpu_ptr(&xen_clock_events.evt));
374 }
375 
xen_timer_resume(void)376 void xen_timer_resume(void)
377 {
378 	int cpu;
379 
380 	if (xen_clockevent != &xen_vcpuop_clockevent)
381 		return;
382 
383 	for_each_online_cpu(cpu) {
384 		if (HYPERVISOR_vcpu_op(VCPUOP_stop_periodic_timer,
385 				       xen_vcpu_nr(cpu), NULL))
386 			BUG();
387 	}
388 }
389 
390 static struct pvclock_vsyscall_time_info *xen_clock __read_mostly;
391 static u64 xen_clock_value_saved;
392 
xen_save_time_memory_area(void)393 void xen_save_time_memory_area(void)
394 {
395 	struct vcpu_register_time_memory_area t;
396 	int ret;
397 
398 	xen_clock_value_saved = xen_clocksource_read() - xen_sched_clock_offset;
399 
400 	if (!xen_clock)
401 		return;
402 
403 	t.addr.v = NULL;
404 
405 	ret = HYPERVISOR_vcpu_op(VCPUOP_register_vcpu_time_memory_area, 0, &t);
406 	if (ret != 0)
407 		pr_notice("Cannot save secondary vcpu_time_info (err %d)",
408 			  ret);
409 	else
410 		clear_page(xen_clock);
411 }
412 
xen_restore_time_memory_area(void)413 void xen_restore_time_memory_area(void)
414 {
415 	struct vcpu_register_time_memory_area t;
416 	int ret;
417 
418 	if (!xen_clock)
419 		goto out;
420 
421 	t.addr.v = &xen_clock->pvti;
422 
423 	ret = HYPERVISOR_vcpu_op(VCPUOP_register_vcpu_time_memory_area, 0, &t);
424 
425 	/*
426 	 * We don't disable VDSO_CLOCKMODE_PVCLOCK entirely if it fails to
427 	 * register the secondary time info with Xen or if we migrated to a
428 	 * host without the necessary flags. On both of these cases what
429 	 * happens is either process seeing a zeroed out pvti or seeing no
430 	 * PVCLOCK_TSC_STABLE_BIT bit set. Userspace checks the latter and
431 	 * if 0, it discards the data in pvti and fallbacks to a system
432 	 * call for a reliable timestamp.
433 	 */
434 	if (ret != 0)
435 		pr_notice("Cannot restore secondary vcpu_time_info (err %d)",
436 			  ret);
437 
438 out:
439 	/* Need pvclock_resume() before using xen_clocksource_read(). */
440 	pvclock_resume();
441 	xen_sched_clock_offset = xen_clocksource_read() - xen_clock_value_saved;
442 }
443 
xen_setup_vsyscall_time_info(void)444 static void xen_setup_vsyscall_time_info(void)
445 {
446 	struct vcpu_register_time_memory_area t;
447 	struct pvclock_vsyscall_time_info *ti;
448 	int ret;
449 
450 	ti = (struct pvclock_vsyscall_time_info *)get_zeroed_page(GFP_KERNEL);
451 	if (!ti)
452 		return;
453 
454 	t.addr.v = &ti->pvti;
455 
456 	ret = HYPERVISOR_vcpu_op(VCPUOP_register_vcpu_time_memory_area, 0, &t);
457 	if (ret) {
458 		pr_notice("xen: VDSO_CLOCKMODE_PVCLOCK not supported (err %d)\n", ret);
459 		free_page((unsigned long)ti);
460 		return;
461 	}
462 
463 	/*
464 	 * If primary time info had this bit set, secondary should too since
465 	 * it's the same data on both just different memory regions. But we
466 	 * still check it in case hypervisor is buggy.
467 	 */
468 	if (!(ti->pvti.flags & PVCLOCK_TSC_STABLE_BIT)) {
469 		t.addr.v = NULL;
470 		ret = HYPERVISOR_vcpu_op(VCPUOP_register_vcpu_time_memory_area,
471 					 0, &t);
472 		if (!ret)
473 			free_page((unsigned long)ti);
474 
475 		pr_notice("xen: VDSO_CLOCKMODE_PVCLOCK not supported (tsc unstable)\n");
476 		return;
477 	}
478 
479 	xen_clock = ti;
480 	pvclock_set_pvti_cpu0_va(xen_clock);
481 
482 	xen_clocksource.vdso_clock_mode = VDSO_CLOCKMODE_PVCLOCK;
483 }
484 
485 /*
486  * Check if it is possible to safely use the tsc as a clocksource.  This is
487  * only true if the hypervisor notifies the guest that its tsc is invariant,
488  * the tsc is stable, and the tsc instruction will never be emulated.
489  */
xen_tsc_safe_clocksource(void)490 static int __init xen_tsc_safe_clocksource(void)
491 {
492 	u32 eax, ebx, ecx, edx;
493 
494 	if (!(boot_cpu_has(X86_FEATURE_CONSTANT_TSC)))
495 		return 0;
496 
497 	if (!(boot_cpu_has(X86_FEATURE_NONSTOP_TSC)))
498 		return 0;
499 
500 	if (check_tsc_unstable())
501 		return 0;
502 
503 	/* Leaf 4, sub-leaf 0 (0x40000x03) */
504 	cpuid_count(xen_cpuid_base() + 3, 0, &eax, &ebx, &ecx, &edx);
505 
506 	return ebx == XEN_CPUID_TSC_MODE_NEVER_EMULATE;
507 }
508 
xen_time_init(void)509 static void __init xen_time_init(void)
510 {
511 	struct pvclock_vcpu_time_info *pvti;
512 	int cpu = smp_processor_id();
513 	struct timespec64 tp;
514 
515 	/*
516 	 * As Dom0 is never moved, no penalty on using TSC there.
517 	 *
518 	 * If it is possible for the guest to determine that the tsc is a safe
519 	 * clocksource, then set xen_clocksource rating below that of the tsc
520 	 * so that the system prefers tsc instead.
521 	 */
522 	if (xen_initial_domain())
523 		xen_clocksource.rating = 275;
524 	else if (xen_tsc_safe_clocksource())
525 		xen_clocksource.rating = 299;
526 
527 	clocksource_register_hz(&xen_clocksource, NSEC_PER_SEC);
528 
529 	if (HYPERVISOR_vcpu_op(VCPUOP_stop_periodic_timer, xen_vcpu_nr(cpu),
530 			       NULL) == 0) {
531 		/* Successfully turned off 100Hz tick, so we have the
532 		   vcpuop-based timer interface */
533 		printk(KERN_DEBUG "Xen: using vcpuop timer interface\n");
534 		xen_clockevent = &xen_vcpuop_clockevent;
535 	}
536 
537 	/* Set initial system time with full resolution */
538 	xen_read_wallclock(&tp);
539 	do_settimeofday64(&tp);
540 
541 	setup_force_cpu_cap(X86_FEATURE_TSC);
542 
543 	/*
544 	 * We check ahead on the primary time info if this
545 	 * bit is supported hence speeding up Xen clocksource.
546 	 */
547 	pvti = &__this_cpu_read(xen_vcpu)->time;
548 	if (pvti->flags & PVCLOCK_TSC_STABLE_BIT) {
549 		pvclock_set_flags(PVCLOCK_TSC_STABLE_BIT);
550 		xen_setup_vsyscall_time_info();
551 	}
552 
553 	xen_setup_runstate_info(cpu);
554 	xen_setup_timer(cpu);
555 	xen_setup_cpu_clockevents();
556 
557 	xen_time_setup_guest();
558 
559 	if (xen_initial_domain())
560 		pvclock_gtod_register_notifier(&xen_pvclock_gtod_notifier);
561 }
562 
xen_init_time_common(void)563 static void __init xen_init_time_common(void)
564 {
565 	xen_sched_clock_offset = xen_clocksource_read();
566 	static_call_update(pv_steal_clock, xen_steal_clock);
567 	paravirt_set_sched_clock(xen_sched_clock);
568 
569 	x86_platform.calibrate_tsc = xen_tsc_khz;
570 	x86_platform.get_wallclock = xen_get_wallclock;
571 }
572 
xen_init_time_ops(void)573 void __init xen_init_time_ops(void)
574 {
575 	xen_init_time_common();
576 
577 	x86_init.timers.timer_init = xen_time_init;
578 	x86_init.timers.setup_percpu_clockev = x86_init_noop;
579 	x86_cpuinit.setup_percpu_clockev = x86_init_noop;
580 
581 	/* Dom0 uses the native method to set the hardware RTC. */
582 	if (!xen_initial_domain())
583 		x86_platform.set_wallclock = xen_set_wallclock;
584 }
585 
586 #ifdef CONFIG_XEN_PVHVM
xen_hvm_setup_cpu_clockevents(void)587 static void xen_hvm_setup_cpu_clockevents(void)
588 {
589 	int cpu = smp_processor_id();
590 	xen_setup_runstate_info(cpu);
591 	/*
592 	 * xen_setup_timer(cpu) - snprintf is bad in atomic context. Hence
593 	 * doing it xen_hvm_cpu_notify (which gets called by smp_init during
594 	 * early bootup and also during CPU hotplug events).
595 	 */
596 	xen_setup_cpu_clockevents();
597 }
598 
xen_hvm_init_time_ops(void)599 void __init xen_hvm_init_time_ops(void)
600 {
601 	static bool hvm_time_initialized;
602 
603 	if (hvm_time_initialized)
604 		return;
605 
606 	/*
607 	 * vector callback is needed otherwise we cannot receive interrupts
608 	 * on cpu > 0 and at this point we don't know how many cpus are
609 	 * available.
610 	 */
611 	if (!xen_have_vector_callback)
612 		return;
613 
614 	if (!xen_feature(XENFEAT_hvm_safe_pvclock)) {
615 		pr_info_once("Xen doesn't support pvclock on HVM, disable pv timer");
616 		return;
617 	}
618 
619 	/*
620 	 * Only MAX_VIRT_CPUS 'vcpu_info' are embedded inside 'shared_info'.
621 	 * The __this_cpu_read(xen_vcpu) is still NULL when Xen HVM guest
622 	 * boots on vcpu >= MAX_VIRT_CPUS (e.g., kexec), To access
623 	 * __this_cpu_read(xen_vcpu) via xen_clocksource_read() will panic.
624 	 *
625 	 * The xen_hvm_init_time_ops() should be called again later after
626 	 * __this_cpu_read(xen_vcpu) is available.
627 	 */
628 	if (!__this_cpu_read(xen_vcpu)) {
629 		pr_info("Delay xen_init_time_common() as kernel is running on vcpu=%d\n",
630 			xen_vcpu_nr(0));
631 		return;
632 	}
633 
634 	xen_init_time_common();
635 
636 	x86_init.timers.setup_percpu_clockev = xen_time_init;
637 	x86_cpuinit.setup_percpu_clockev = xen_hvm_setup_cpu_clockevents;
638 
639 	x86_platform.set_wallclock = xen_set_wallclock;
640 
641 	hvm_time_initialized = true;
642 }
643 #endif
644 
645 /* Kernel parameter to specify Xen timer slop */
parse_xen_timer_slop(char * ptr)646 static int __init parse_xen_timer_slop(char *ptr)
647 {
648 	unsigned long slop = memparse(ptr, NULL);
649 
650 	xen_timerop_clockevent.min_delta_ns = slop;
651 	xen_timerop_clockevent.min_delta_ticks = slop;
652 	xen_vcpuop_clockevent.min_delta_ns = slop;
653 	xen_vcpuop_clockevent.min_delta_ticks = slop;
654 
655 	return 0;
656 }
657 early_param("xen_timer_slop", parse_xen_timer_slop);
658