xref: /linux/drivers/xen/balloon.c (revision 2bc46b3ad3c15165f91459b07ff8682478683194)
1 /******************************************************************************
2  * Xen balloon driver - enables returning/claiming memory to/from Xen.
3  *
4  * Copyright (c) 2003, B Dragovic
5  * Copyright (c) 2003-2004, M Williamson, K Fraser
6  * Copyright (c) 2005 Dan M. Smith, IBM Corporation
7  * Copyright (c) 2010 Daniel Kiper
8  *
9  * Memory hotplug support was written by Daniel Kiper. Work on
10  * it was sponsored by Google under Google Summer of Code 2010
11  * program. Jeremy Fitzhardinge from Citrix was the mentor for
12  * this project.
13  *
14  * This program is free software; you can redistribute it and/or
15  * modify it under the terms of the GNU General Public License version 2
16  * as published by the Free Software Foundation; or, when distributed
17  * separately from the Linux kernel or incorporated into other
18  * software packages, subject to the following license:
19  *
20  * Permission is hereby granted, free of charge, to any person obtaining a copy
21  * of this source file (the "Software"), to deal in the Software without
22  * restriction, including without limitation the rights to use, copy, modify,
23  * merge, publish, distribute, sublicense, and/or sell copies of the Software,
24  * and to permit persons to whom the Software is furnished to do so, subject to
25  * the following conditions:
26  *
27  * The above copyright notice and this permission notice shall be included in
28  * all copies or substantial portions of the Software.
29  *
30  * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
31  * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
32  * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
33  * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
34  * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
35  * FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS
36  * IN THE SOFTWARE.
37  */
38 
39 #define pr_fmt(fmt) "xen:" KBUILD_MODNAME ": " fmt
40 
41 #include <linux/cpu.h>
42 #include <linux/kernel.h>
43 #include <linux/sched.h>
44 #include <linux/errno.h>
45 #include <linux/mm.h>
46 #include <linux/bootmem.h>
47 #include <linux/pagemap.h>
48 #include <linux/highmem.h>
49 #include <linux/mutex.h>
50 #include <linux/list.h>
51 #include <linux/gfp.h>
52 #include <linux/notifier.h>
53 #include <linux/memory.h>
54 #include <linux/memory_hotplug.h>
55 #include <linux/percpu-defs.h>
56 #include <linux/slab.h>
57 #include <linux/sysctl.h>
58 
59 #include <asm/page.h>
60 #include <asm/pgalloc.h>
61 #include <asm/pgtable.h>
62 #include <asm/tlb.h>
63 
64 #include <asm/xen/hypervisor.h>
65 #include <asm/xen/hypercall.h>
66 
67 #include <xen/xen.h>
68 #include <xen/interface/xen.h>
69 #include <xen/interface/memory.h>
70 #include <xen/balloon.h>
71 #include <xen/features.h>
72 #include <xen/page.h>
73 
74 static int xen_hotplug_unpopulated;
75 
76 #ifdef CONFIG_XEN_BALLOON_MEMORY_HOTPLUG
77 
78 static int zero;
79 static int one = 1;
80 
81 static struct ctl_table balloon_table[] = {
82 	{
83 		.procname	= "hotplug_unpopulated",
84 		.data		= &xen_hotplug_unpopulated,
85 		.maxlen		= sizeof(int),
86 		.mode		= 0644,
87 		.proc_handler	= proc_dointvec_minmax,
88 		.extra1         = &zero,
89 		.extra2         = &one,
90 	},
91 	{ }
92 };
93 
94 static struct ctl_table balloon_root[] = {
95 	{
96 		.procname	= "balloon",
97 		.mode		= 0555,
98 		.child		= balloon_table,
99 	},
100 	{ }
101 };
102 
103 static struct ctl_table xen_root[] = {
104 	{
105 		.procname	= "xen",
106 		.mode		= 0555,
107 		.child		= balloon_root,
108 	},
109 	{ }
110 };
111 
112 #endif
113 
114 /*
115  * Use one extent per PAGE_SIZE to avoid to break down the page into
116  * multiple frame.
117  */
118 #define EXTENT_ORDER (fls(XEN_PFN_PER_PAGE) - 1)
119 
120 /*
121  * balloon_process() state:
122  *
123  * BP_DONE: done or nothing to do,
124  * BP_WAIT: wait to be rescheduled,
125  * BP_EAGAIN: error, go to sleep,
126  * BP_ECANCELED: error, balloon operation canceled.
127  */
128 
129 enum bp_state {
130 	BP_DONE,
131 	BP_WAIT,
132 	BP_EAGAIN,
133 	BP_ECANCELED
134 };
135 
136 
137 static DEFINE_MUTEX(balloon_mutex);
138 
139 struct balloon_stats balloon_stats;
140 EXPORT_SYMBOL_GPL(balloon_stats);
141 
142 /* We increase/decrease in batches which fit in a page */
143 static xen_pfn_t frame_list[PAGE_SIZE / sizeof(xen_pfn_t)];
144 
145 
146 /* List of ballooned pages, threaded through the mem_map array. */
147 static LIST_HEAD(ballooned_pages);
148 static DECLARE_WAIT_QUEUE_HEAD(balloon_wq);
149 
150 /* Main work function, always executed in process context. */
151 static void balloon_process(struct work_struct *work);
152 static DECLARE_DELAYED_WORK(balloon_worker, balloon_process);
153 
154 static void release_memory_resource(struct resource *resource);
155 
156 /* When ballooning out (allocating memory to return to Xen) we don't really
157    want the kernel to try too hard since that can trigger the oom killer. */
158 #define GFP_BALLOON \
159 	(GFP_HIGHUSER | __GFP_NOWARN | __GFP_NORETRY | __GFP_NOMEMALLOC)
160 
161 static void scrub_page(struct page *page)
162 {
163 #ifdef CONFIG_XEN_SCRUB_PAGES
164 	clear_highpage(page);
165 #endif
166 }
167 
168 /* balloon_append: add the given page to the balloon. */
169 static void __balloon_append(struct page *page)
170 {
171 	/* Lowmem is re-populated first, so highmem pages go at list tail. */
172 	if (PageHighMem(page)) {
173 		list_add_tail(&page->lru, &ballooned_pages);
174 		balloon_stats.balloon_high++;
175 	} else {
176 		list_add(&page->lru, &ballooned_pages);
177 		balloon_stats.balloon_low++;
178 	}
179 	wake_up(&balloon_wq);
180 }
181 
182 static void balloon_append(struct page *page)
183 {
184 	__balloon_append(page);
185 	adjust_managed_page_count(page, -1);
186 }
187 
188 /* balloon_retrieve: rescue a page from the balloon, if it is not empty. */
189 static struct page *balloon_retrieve(bool require_lowmem)
190 {
191 	struct page *page;
192 
193 	if (list_empty(&ballooned_pages))
194 		return NULL;
195 
196 	page = list_entry(ballooned_pages.next, struct page, lru);
197 	if (require_lowmem && PageHighMem(page))
198 		return NULL;
199 	list_del(&page->lru);
200 
201 	if (PageHighMem(page))
202 		balloon_stats.balloon_high--;
203 	else
204 		balloon_stats.balloon_low--;
205 
206 	adjust_managed_page_count(page, 1);
207 
208 	return page;
209 }
210 
211 static struct page *balloon_next_page(struct page *page)
212 {
213 	struct list_head *next = page->lru.next;
214 	if (next == &ballooned_pages)
215 		return NULL;
216 	return list_entry(next, struct page, lru);
217 }
218 
219 static enum bp_state update_schedule(enum bp_state state)
220 {
221 	if (state == BP_WAIT)
222 		return BP_WAIT;
223 
224 	if (state == BP_ECANCELED)
225 		return BP_ECANCELED;
226 
227 	if (state == BP_DONE) {
228 		balloon_stats.schedule_delay = 1;
229 		balloon_stats.retry_count = 1;
230 		return BP_DONE;
231 	}
232 
233 	++balloon_stats.retry_count;
234 
235 	if (balloon_stats.max_retry_count != RETRY_UNLIMITED &&
236 			balloon_stats.retry_count > balloon_stats.max_retry_count) {
237 		balloon_stats.schedule_delay = 1;
238 		balloon_stats.retry_count = 1;
239 		return BP_ECANCELED;
240 	}
241 
242 	balloon_stats.schedule_delay <<= 1;
243 
244 	if (balloon_stats.schedule_delay > balloon_stats.max_schedule_delay)
245 		balloon_stats.schedule_delay = balloon_stats.max_schedule_delay;
246 
247 	return BP_EAGAIN;
248 }
249 
250 #ifdef CONFIG_XEN_BALLOON_MEMORY_HOTPLUG
251 static struct resource *additional_memory_resource(phys_addr_t size)
252 {
253 	struct resource *res;
254 	int ret;
255 
256 	res = kzalloc(sizeof(*res), GFP_KERNEL);
257 	if (!res)
258 		return NULL;
259 
260 	res->name = "System RAM";
261 	res->flags = IORESOURCE_SYSTEM_RAM | IORESOURCE_BUSY;
262 
263 	ret = allocate_resource(&iomem_resource, res,
264 				size, 0, -1,
265 				PAGES_PER_SECTION * PAGE_SIZE, NULL, NULL);
266 	if (ret < 0) {
267 		pr_err("Cannot allocate new System RAM resource\n");
268 		kfree(res);
269 		return NULL;
270 	}
271 
272 #ifdef CONFIG_SPARSEMEM
273 	{
274 		unsigned long limit = 1UL << (MAX_PHYSMEM_BITS - PAGE_SHIFT);
275 		unsigned long pfn = res->start >> PAGE_SHIFT;
276 
277 		if (pfn > limit) {
278 			pr_err("New System RAM resource outside addressable RAM (%lu > %lu)\n",
279 			       pfn, limit);
280 			release_memory_resource(res);
281 			return NULL;
282 		}
283 	}
284 #endif
285 
286 	return res;
287 }
288 
289 static void release_memory_resource(struct resource *resource)
290 {
291 	if (!resource)
292 		return;
293 
294 	/*
295 	 * No need to reset region to identity mapped since we now
296 	 * know that no I/O can be in this region
297 	 */
298 	release_resource(resource);
299 	kfree(resource);
300 }
301 
302 static enum bp_state reserve_additional_memory(void)
303 {
304 	long credit;
305 	struct resource *resource;
306 	int nid, rc;
307 	unsigned long balloon_hotplug;
308 
309 	credit = balloon_stats.target_pages + balloon_stats.target_unpopulated
310 		- balloon_stats.total_pages;
311 
312 	/*
313 	 * Already hotplugged enough pages?  Wait for them to be
314 	 * onlined.
315 	 */
316 	if (credit <= 0)
317 		return BP_WAIT;
318 
319 	balloon_hotplug = round_up(credit, PAGES_PER_SECTION);
320 
321 	resource = additional_memory_resource(balloon_hotplug * PAGE_SIZE);
322 	if (!resource)
323 		goto err;
324 
325 	nid = memory_add_physaddr_to_nid(resource->start);
326 
327 #ifdef CONFIG_XEN_HAVE_PVMMU
328 	/*
329 	 * We don't support PV MMU when Linux and Xen is using
330 	 * different page granularity.
331 	 */
332 	BUILD_BUG_ON(XEN_PAGE_SIZE != PAGE_SIZE);
333 
334         /*
335          * add_memory() will build page tables for the new memory so
336          * the p2m must contain invalid entries so the correct
337          * non-present PTEs will be written.
338          *
339          * If a failure occurs, the original (identity) p2m entries
340          * are not restored since this region is now known not to
341          * conflict with any devices.
342          */
343 	if (!xen_feature(XENFEAT_auto_translated_physmap)) {
344 		unsigned long pfn, i;
345 
346 		pfn = PFN_DOWN(resource->start);
347 		for (i = 0; i < balloon_hotplug; i++) {
348 			if (!set_phys_to_machine(pfn + i, INVALID_P2M_ENTRY)) {
349 				pr_warn("set_phys_to_machine() failed, no memory added\n");
350 				goto err;
351 			}
352                 }
353 	}
354 #endif
355 
356 	/*
357 	 * add_memory_resource() will call online_pages() which in its turn
358 	 * will call xen_online_page() callback causing deadlock if we don't
359 	 * release balloon_mutex here. Unlocking here is safe because the
360 	 * callers drop the mutex before trying again.
361 	 */
362 	mutex_unlock(&balloon_mutex);
363 	rc = add_memory_resource(nid, resource, memhp_auto_online);
364 	mutex_lock(&balloon_mutex);
365 
366 	if (rc) {
367 		pr_warn("Cannot add additional memory (%i)\n", rc);
368 		goto err;
369 	}
370 
371 	balloon_stats.total_pages += balloon_hotplug;
372 
373 	return BP_WAIT;
374   err:
375 	release_memory_resource(resource);
376 	return BP_ECANCELED;
377 }
378 
379 static void xen_online_page(struct page *page)
380 {
381 	__online_page_set_limits(page);
382 
383 	mutex_lock(&balloon_mutex);
384 
385 	__balloon_append(page);
386 
387 	mutex_unlock(&balloon_mutex);
388 }
389 
390 static int xen_memory_notifier(struct notifier_block *nb, unsigned long val, void *v)
391 {
392 	if (val == MEM_ONLINE)
393 		schedule_delayed_work(&balloon_worker, 0);
394 
395 	return NOTIFY_OK;
396 }
397 
398 static struct notifier_block xen_memory_nb = {
399 	.notifier_call = xen_memory_notifier,
400 	.priority = 0
401 };
402 #else
403 static enum bp_state reserve_additional_memory(void)
404 {
405 	balloon_stats.target_pages = balloon_stats.current_pages;
406 	return BP_ECANCELED;
407 }
408 #endif /* CONFIG_XEN_BALLOON_MEMORY_HOTPLUG */
409 
410 static long current_credit(void)
411 {
412 	return balloon_stats.target_pages - balloon_stats.current_pages;
413 }
414 
415 static bool balloon_is_inflated(void)
416 {
417 	return balloon_stats.balloon_low || balloon_stats.balloon_high;
418 }
419 
420 static enum bp_state increase_reservation(unsigned long nr_pages)
421 {
422 	int rc;
423 	unsigned long i;
424 	struct page   *page;
425 	struct xen_memory_reservation reservation = {
426 		.address_bits = 0,
427 		.extent_order = EXTENT_ORDER,
428 		.domid        = DOMID_SELF
429 	};
430 
431 	if (nr_pages > ARRAY_SIZE(frame_list))
432 		nr_pages = ARRAY_SIZE(frame_list);
433 
434 	page = list_first_entry_or_null(&ballooned_pages, struct page, lru);
435 	for (i = 0; i < nr_pages; i++) {
436 		if (!page) {
437 			nr_pages = i;
438 			break;
439 		}
440 
441 		/* XENMEM_populate_physmap requires a PFN based on Xen
442 		 * granularity.
443 		 */
444 		frame_list[i] = page_to_xen_pfn(page);
445 		page = balloon_next_page(page);
446 	}
447 
448 	set_xen_guest_handle(reservation.extent_start, frame_list);
449 	reservation.nr_extents = nr_pages;
450 	rc = HYPERVISOR_memory_op(XENMEM_populate_physmap, &reservation);
451 	if (rc <= 0)
452 		return BP_EAGAIN;
453 
454 	for (i = 0; i < rc; i++) {
455 		page = balloon_retrieve(false);
456 		BUG_ON(page == NULL);
457 
458 #ifdef CONFIG_XEN_HAVE_PVMMU
459 		/*
460 		 * We don't support PV MMU when Linux and Xen is using
461 		 * different page granularity.
462 		 */
463 		BUILD_BUG_ON(XEN_PAGE_SIZE != PAGE_SIZE);
464 
465 		if (!xen_feature(XENFEAT_auto_translated_physmap)) {
466 			unsigned long pfn = page_to_pfn(page);
467 
468 			set_phys_to_machine(pfn, frame_list[i]);
469 
470 			/* Link back into the page tables if not highmem. */
471 			if (!PageHighMem(page)) {
472 				int ret;
473 				ret = HYPERVISOR_update_va_mapping(
474 						(unsigned long)__va(pfn << PAGE_SHIFT),
475 						mfn_pte(frame_list[i], PAGE_KERNEL),
476 						0);
477 				BUG_ON(ret);
478 			}
479 		}
480 #endif
481 
482 		/* Relinquish the page back to the allocator. */
483 		__free_reserved_page(page);
484 	}
485 
486 	balloon_stats.current_pages += rc;
487 
488 	return BP_DONE;
489 }
490 
491 static enum bp_state decrease_reservation(unsigned long nr_pages, gfp_t gfp)
492 {
493 	enum bp_state state = BP_DONE;
494 	unsigned long i;
495 	struct page *page, *tmp;
496 	int ret;
497 	struct xen_memory_reservation reservation = {
498 		.address_bits = 0,
499 		.extent_order = EXTENT_ORDER,
500 		.domid        = DOMID_SELF
501 	};
502 	LIST_HEAD(pages);
503 
504 	if (nr_pages > ARRAY_SIZE(frame_list))
505 		nr_pages = ARRAY_SIZE(frame_list);
506 
507 	for (i = 0; i < nr_pages; i++) {
508 		page = alloc_page(gfp);
509 		if (page == NULL) {
510 			nr_pages = i;
511 			state = BP_EAGAIN;
512 			break;
513 		}
514 		scrub_page(page);
515 		list_add(&page->lru, &pages);
516 	}
517 
518 	/*
519 	 * Ensure that ballooned highmem pages don't have kmaps.
520 	 *
521 	 * Do this before changing the p2m as kmap_flush_unused()
522 	 * reads PTEs to obtain pages (and hence needs the original
523 	 * p2m entry).
524 	 */
525 	kmap_flush_unused();
526 
527 	/*
528 	 * Setup the frame, update direct mapping, invalidate P2M,
529 	 * and add to balloon.
530 	 */
531 	i = 0;
532 	list_for_each_entry_safe(page, tmp, &pages, lru) {
533 		/* XENMEM_decrease_reservation requires a GFN */
534 		frame_list[i++] = xen_page_to_gfn(page);
535 
536 #ifdef CONFIG_XEN_HAVE_PVMMU
537 		/*
538 		 * We don't support PV MMU when Linux and Xen is using
539 		 * different page granularity.
540 		 */
541 		BUILD_BUG_ON(XEN_PAGE_SIZE != PAGE_SIZE);
542 
543 		if (!xen_feature(XENFEAT_auto_translated_physmap)) {
544 			unsigned long pfn = page_to_pfn(page);
545 
546 			if (!PageHighMem(page)) {
547 				ret = HYPERVISOR_update_va_mapping(
548 						(unsigned long)__va(pfn << PAGE_SHIFT),
549 						__pte_ma(0), 0);
550 				BUG_ON(ret);
551 			}
552 			__set_phys_to_machine(pfn, INVALID_P2M_ENTRY);
553 		}
554 #endif
555 		list_del(&page->lru);
556 
557 		balloon_append(page);
558 	}
559 
560 	flush_tlb_all();
561 
562 	set_xen_guest_handle(reservation.extent_start, frame_list);
563 	reservation.nr_extents   = nr_pages;
564 	ret = HYPERVISOR_memory_op(XENMEM_decrease_reservation, &reservation);
565 	BUG_ON(ret != nr_pages);
566 
567 	balloon_stats.current_pages -= nr_pages;
568 
569 	return state;
570 }
571 
572 /*
573  * As this is a work item it is guaranteed to run as a single instance only.
574  * We may of course race updates of the target counts (which are protected
575  * by the balloon lock), or with changes to the Xen hard limit, but we will
576  * recover from these in time.
577  */
578 static void balloon_process(struct work_struct *work)
579 {
580 	enum bp_state state = BP_DONE;
581 	long credit;
582 
583 
584 	do {
585 		mutex_lock(&balloon_mutex);
586 
587 		credit = current_credit();
588 
589 		if (credit > 0) {
590 			if (balloon_is_inflated())
591 				state = increase_reservation(credit);
592 			else
593 				state = reserve_additional_memory();
594 		}
595 
596 		if (credit < 0)
597 			state = decrease_reservation(-credit, GFP_BALLOON);
598 
599 		state = update_schedule(state);
600 
601 		mutex_unlock(&balloon_mutex);
602 
603 		cond_resched();
604 
605 	} while (credit && state == BP_DONE);
606 
607 	/* Schedule more work if there is some still to be done. */
608 	if (state == BP_EAGAIN)
609 		schedule_delayed_work(&balloon_worker, balloon_stats.schedule_delay * HZ);
610 }
611 
612 /* Resets the Xen limit, sets new target, and kicks off processing. */
613 void balloon_set_new_target(unsigned long target)
614 {
615 	/* No need for lock. Not read-modify-write updates. */
616 	balloon_stats.target_pages = target;
617 	schedule_delayed_work(&balloon_worker, 0);
618 }
619 EXPORT_SYMBOL_GPL(balloon_set_new_target);
620 
621 static int add_ballooned_pages(int nr_pages)
622 {
623 	enum bp_state st;
624 
625 	if (xen_hotplug_unpopulated) {
626 		st = reserve_additional_memory();
627 		if (st != BP_ECANCELED) {
628 			mutex_unlock(&balloon_mutex);
629 			wait_event(balloon_wq,
630 				   !list_empty(&ballooned_pages));
631 			mutex_lock(&balloon_mutex);
632 			return 0;
633 		}
634 	}
635 
636 	st = decrease_reservation(nr_pages, GFP_USER);
637 	if (st != BP_DONE)
638 		return -ENOMEM;
639 
640 	return 0;
641 }
642 
643 /**
644  * alloc_xenballooned_pages - get pages that have been ballooned out
645  * @nr_pages: Number of pages to get
646  * @pages: pages returned
647  * @return 0 on success, error otherwise
648  */
649 int alloc_xenballooned_pages(int nr_pages, struct page **pages)
650 {
651 	int pgno = 0;
652 	struct page *page;
653 	int ret;
654 
655 	mutex_lock(&balloon_mutex);
656 
657 	balloon_stats.target_unpopulated += nr_pages;
658 
659 	while (pgno < nr_pages) {
660 		page = balloon_retrieve(true);
661 		if (page) {
662 			pages[pgno++] = page;
663 #ifdef CONFIG_XEN_HAVE_PVMMU
664 			/*
665 			 * We don't support PV MMU when Linux and Xen is using
666 			 * different page granularity.
667 			 */
668 			BUILD_BUG_ON(XEN_PAGE_SIZE != PAGE_SIZE);
669 
670 			ret = xen_alloc_p2m_entry(page_to_pfn(page));
671 			if (ret < 0)
672 				goto out_undo;
673 #endif
674 		} else {
675 			ret = add_ballooned_pages(nr_pages - pgno);
676 			if (ret < 0)
677 				goto out_undo;
678 		}
679 	}
680 	mutex_unlock(&balloon_mutex);
681 	return 0;
682  out_undo:
683 	mutex_unlock(&balloon_mutex);
684 	free_xenballooned_pages(pgno, pages);
685 	return ret;
686 }
687 EXPORT_SYMBOL(alloc_xenballooned_pages);
688 
689 /**
690  * free_xenballooned_pages - return pages retrieved with get_ballooned_pages
691  * @nr_pages: Number of pages
692  * @pages: pages to return
693  */
694 void free_xenballooned_pages(int nr_pages, struct page **pages)
695 {
696 	int i;
697 
698 	mutex_lock(&balloon_mutex);
699 
700 	for (i = 0; i < nr_pages; i++) {
701 		if (pages[i])
702 			balloon_append(pages[i]);
703 	}
704 
705 	balloon_stats.target_unpopulated -= nr_pages;
706 
707 	/* The balloon may be too large now. Shrink it if needed. */
708 	if (current_credit())
709 		schedule_delayed_work(&balloon_worker, 0);
710 
711 	mutex_unlock(&balloon_mutex);
712 }
713 EXPORT_SYMBOL(free_xenballooned_pages);
714 
715 static void __init balloon_add_region(unsigned long start_pfn,
716 				      unsigned long pages)
717 {
718 	unsigned long pfn, extra_pfn_end;
719 	struct page *page;
720 
721 	/*
722 	 * If the amount of usable memory has been limited (e.g., with
723 	 * the 'mem' command line parameter), don't add pages beyond
724 	 * this limit.
725 	 */
726 	extra_pfn_end = min(max_pfn, start_pfn + pages);
727 
728 	for (pfn = start_pfn; pfn < extra_pfn_end; pfn++) {
729 		page = pfn_to_page(pfn);
730 		/* totalram_pages and totalhigh_pages do not
731 		   include the boot-time balloon extension, so
732 		   don't subtract from it. */
733 		__balloon_append(page);
734 	}
735 
736 	balloon_stats.total_pages += extra_pfn_end - start_pfn;
737 }
738 
739 static int __init balloon_init(void)
740 {
741 	int i;
742 
743 	if (!xen_domain())
744 		return -ENODEV;
745 
746 	pr_info("Initialising balloon driver\n");
747 
748 	balloon_stats.current_pages = xen_pv_domain()
749 		? min(xen_start_info->nr_pages - xen_released_pages, max_pfn)
750 		: get_num_physpages();
751 	balloon_stats.target_pages  = balloon_stats.current_pages;
752 	balloon_stats.balloon_low   = 0;
753 	balloon_stats.balloon_high  = 0;
754 	balloon_stats.total_pages   = balloon_stats.current_pages;
755 
756 	balloon_stats.schedule_delay = 1;
757 	balloon_stats.max_schedule_delay = 32;
758 	balloon_stats.retry_count = 1;
759 	balloon_stats.max_retry_count = RETRY_UNLIMITED;
760 
761 #ifdef CONFIG_XEN_BALLOON_MEMORY_HOTPLUG
762 	set_online_page_callback(&xen_online_page);
763 	register_memory_notifier(&xen_memory_nb);
764 	register_sysctl_table(xen_root);
765 #endif
766 
767 	/*
768 	 * Initialize the balloon with pages from the extra memory
769 	 * regions (see arch/x86/xen/setup.c).
770 	 */
771 	for (i = 0; i < XEN_EXTRA_MEM_MAX_REGIONS; i++)
772 		if (xen_extra_mem[i].n_pfns)
773 			balloon_add_region(xen_extra_mem[i].start_pfn,
774 					   xen_extra_mem[i].n_pfns);
775 
776 	return 0;
777 }
778 subsys_initcall(balloon_init);
779