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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
74static int xen_hotplug_unpopulated;
75
76#ifdef CONFIG_XEN_BALLOON_MEMORY_HOTPLUG
77
78static int zero;
79static int one = 1;
80
81static 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
94static struct ctl_table balloon_root[] = {
95 {
96 .procname = "balloon",
97 .mode = 0555,
98 .child = balloon_table,
99 },
100 { }
101};
102
103static 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
129enum bp_state {
130 BP_DONE,
131 BP_WAIT,
132 BP_EAGAIN,
133 BP_ECANCELED
134};
135
136
137static DEFINE_MUTEX(balloon_mutex);
138
139struct balloon_stats balloon_stats;
140EXPORT_SYMBOL_GPL(balloon_stats);
141
142/* We increase/decrease in batches which fit in a page */
143static xen_pfn_t frame_list[PAGE_SIZE / sizeof(xen_pfn_t)];
144
145
146/* List of ballooned pages, threaded through the mem_map array. */
147static LIST_HEAD(ballooned_pages);
148static DECLARE_WAIT_QUEUE_HEAD(balloon_wq);
149
150/* Main work function, always executed in process context. */
151static void balloon_process(struct work_struct *work);
152static DECLARE_DELAYED_WORK(balloon_worker, balloon_process);
153
154static 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
161static 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. */
169static 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
182static 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. */
189static 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
211static 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
219static 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
251static 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
289static 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
302static 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
379static 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
390static 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
398static struct notifier_block xen_memory_nb = {
399 .notifier_call = xen_memory_notifier,
400 .priority = 0
401};
402#else
403static 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
410static long current_credit(void)
411{
412 return balloon_stats.target_pages - balloon_stats.current_pages;
413}
414
415static bool balloon_is_inflated(void)
416{
417 return balloon_stats.balloon_low || balloon_stats.balloon_high;
418}
419
420static 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
491static 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 */
578static 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. */
613void 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}
619EXPORT_SYMBOL_GPL(balloon_set_new_target);
620
621static 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 */
649int 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}
687EXPORT_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 */
694void 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}
713EXPORT_SYMBOL(free_xenballooned_pages);
714
715static 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
739static 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}
778subsys_initcall(balloon_init);
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
74static int xen_hotplug_unpopulated;
75
76#ifdef CONFIG_XEN_BALLOON_MEMORY_HOTPLUG
77
78static int zero;
79static int one = 1;
80
81static 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
94static struct ctl_table balloon_root[] = {
95 {
96 .procname = "balloon",
97 .mode = 0555,
98 .child = balloon_table,
99 },
100 { }
101};
102
103static 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
129enum bp_state {
130 BP_DONE,
131 BP_WAIT,
132 BP_EAGAIN,
133 BP_ECANCELED
134};
135
136
137static DEFINE_MUTEX(balloon_mutex);
138
139struct balloon_stats balloon_stats;
140EXPORT_SYMBOL_GPL(balloon_stats);
141
142/* We increase/decrease in batches which fit in a page */
143static xen_pfn_t frame_list[PAGE_SIZE / sizeof(xen_pfn_t)];
144
145
146/* List of ballooned pages, threaded through the mem_map array. */
147static LIST_HEAD(ballooned_pages);
148static DECLARE_WAIT_QUEUE_HEAD(balloon_wq);
149
150/* Main work function, always executed in process context. */
151static void balloon_process(struct work_struct *work);
152static DECLARE_DELAYED_WORK(balloon_worker, balloon_process);
153
154/* When ballooning out (allocating memory to return to Xen) we don't really
155 want the kernel to try too hard since that can trigger the oom killer. */
156#define GFP_BALLOON \
157 (GFP_HIGHUSER | __GFP_NOWARN | __GFP_NORETRY | __GFP_NOMEMALLOC)
158
159static void scrub_page(struct page *page)
160{
161#ifdef CONFIG_XEN_SCRUB_PAGES
162 clear_highpage(page);
163#endif
164}
165
166/* balloon_append: add the given page to the balloon. */
167static void __balloon_append(struct page *page)
168{
169 /* Lowmem is re-populated first, so highmem pages go at list tail. */
170 if (PageHighMem(page)) {
171 list_add_tail(&page->lru, &ballooned_pages);
172 balloon_stats.balloon_high++;
173 } else {
174 list_add(&page->lru, &ballooned_pages);
175 balloon_stats.balloon_low++;
176 }
177 wake_up(&balloon_wq);
178}
179
180static void balloon_append(struct page *page)
181{
182 __balloon_append(page);
183}
184
185/* balloon_retrieve: rescue a page from the balloon, if it is not empty. */
186static struct page *balloon_retrieve(bool require_lowmem)
187{
188 struct page *page;
189
190 if (list_empty(&ballooned_pages))
191 return NULL;
192
193 page = list_entry(ballooned_pages.next, struct page, lru);
194 if (require_lowmem && PageHighMem(page))
195 return NULL;
196 list_del(&page->lru);
197
198 if (PageHighMem(page))
199 balloon_stats.balloon_high--;
200 else
201 balloon_stats.balloon_low--;
202
203 return page;
204}
205
206static struct page *balloon_next_page(struct page *page)
207{
208 struct list_head *next = page->lru.next;
209 if (next == &ballooned_pages)
210 return NULL;
211 return list_entry(next, struct page, lru);
212}
213
214static enum bp_state update_schedule(enum bp_state state)
215{
216 if (state == BP_WAIT)
217 return BP_WAIT;
218
219 if (state == BP_ECANCELED)
220 return BP_ECANCELED;
221
222 if (state == BP_DONE) {
223 balloon_stats.schedule_delay = 1;
224 balloon_stats.retry_count = 1;
225 return BP_DONE;
226 }
227
228 ++balloon_stats.retry_count;
229
230 if (balloon_stats.max_retry_count != RETRY_UNLIMITED &&
231 balloon_stats.retry_count > balloon_stats.max_retry_count) {
232 balloon_stats.schedule_delay = 1;
233 balloon_stats.retry_count = 1;
234 return BP_ECANCELED;
235 }
236
237 balloon_stats.schedule_delay <<= 1;
238
239 if (balloon_stats.schedule_delay > balloon_stats.max_schedule_delay)
240 balloon_stats.schedule_delay = balloon_stats.max_schedule_delay;
241
242 return BP_EAGAIN;
243}
244
245#ifdef CONFIG_XEN_BALLOON_MEMORY_HOTPLUG
246static void release_memory_resource(struct resource *resource)
247{
248 if (!resource)
249 return;
250
251 /*
252 * No need to reset region to identity mapped since we now
253 * know that no I/O can be in this region
254 */
255 release_resource(resource);
256 kfree(resource);
257}
258
259static struct resource *additional_memory_resource(phys_addr_t size)
260{
261 struct resource *res;
262 int ret;
263
264 res = kzalloc(sizeof(*res), GFP_KERNEL);
265 if (!res)
266 return NULL;
267
268 res->name = "System RAM";
269 res->flags = IORESOURCE_SYSTEM_RAM | IORESOURCE_BUSY;
270
271 ret = allocate_resource(&iomem_resource, res,
272 size, 0, -1,
273 PAGES_PER_SECTION * PAGE_SIZE, NULL, NULL);
274 if (ret < 0) {
275 pr_err("Cannot allocate new System RAM resource\n");
276 kfree(res);
277 return NULL;
278 }
279
280#ifdef CONFIG_SPARSEMEM
281 {
282 unsigned long limit = 1UL << (MAX_PHYSMEM_BITS - PAGE_SHIFT);
283 unsigned long pfn = res->start >> PAGE_SHIFT;
284
285 if (pfn > limit) {
286 pr_err("New System RAM resource outside addressable RAM (%lu > %lu)\n",
287 pfn, limit);
288 release_memory_resource(res);
289 return NULL;
290 }
291 }
292#endif
293
294 return res;
295}
296
297static enum bp_state reserve_additional_memory(void)
298{
299 long credit;
300 struct resource *resource;
301 int nid, rc;
302 unsigned long balloon_hotplug;
303
304 credit = balloon_stats.target_pages + balloon_stats.target_unpopulated
305 - balloon_stats.total_pages;
306
307 /*
308 * Already hotplugged enough pages? Wait for them to be
309 * onlined.
310 */
311 if (credit <= 0)
312 return BP_WAIT;
313
314 balloon_hotplug = round_up(credit, PAGES_PER_SECTION);
315
316 resource = additional_memory_resource(balloon_hotplug * PAGE_SIZE);
317 if (!resource)
318 goto err;
319
320 nid = memory_add_physaddr_to_nid(resource->start);
321
322#ifdef CONFIG_XEN_HAVE_PVMMU
323 /*
324 * We don't support PV MMU when Linux and Xen is using
325 * different page granularity.
326 */
327 BUILD_BUG_ON(XEN_PAGE_SIZE != PAGE_SIZE);
328
329 /*
330 * add_memory() will build page tables for the new memory so
331 * the p2m must contain invalid entries so the correct
332 * non-present PTEs will be written.
333 *
334 * If a failure occurs, the original (identity) p2m entries
335 * are not restored since this region is now known not to
336 * conflict with any devices.
337 */
338 if (!xen_feature(XENFEAT_auto_translated_physmap)) {
339 unsigned long pfn, i;
340
341 pfn = PFN_DOWN(resource->start);
342 for (i = 0; i < balloon_hotplug; i++) {
343 if (!set_phys_to_machine(pfn + i, INVALID_P2M_ENTRY)) {
344 pr_warn("set_phys_to_machine() failed, no memory added\n");
345 goto err;
346 }
347 }
348 }
349#endif
350
351 /*
352 * add_memory_resource() will call online_pages() which in its turn
353 * will call xen_online_page() callback causing deadlock if we don't
354 * release balloon_mutex here. Unlocking here is safe because the
355 * callers drop the mutex before trying again.
356 */
357 mutex_unlock(&balloon_mutex);
358 rc = add_memory_resource(nid, resource, memhp_auto_online);
359 mutex_lock(&balloon_mutex);
360
361 if (rc) {
362 pr_warn("Cannot add additional memory (%i)\n", rc);
363 goto err;
364 }
365
366 balloon_stats.total_pages += balloon_hotplug;
367
368 return BP_WAIT;
369 err:
370 release_memory_resource(resource);
371 return BP_ECANCELED;
372}
373
374static void xen_online_page(struct page *page)
375{
376 __online_page_set_limits(page);
377
378 mutex_lock(&balloon_mutex);
379
380 __balloon_append(page);
381
382 mutex_unlock(&balloon_mutex);
383}
384
385static int xen_memory_notifier(struct notifier_block *nb, unsigned long val, void *v)
386{
387 if (val == MEM_ONLINE)
388 schedule_delayed_work(&balloon_worker, 0);
389
390 return NOTIFY_OK;
391}
392
393static struct notifier_block xen_memory_nb = {
394 .notifier_call = xen_memory_notifier,
395 .priority = 0
396};
397#else
398static enum bp_state reserve_additional_memory(void)
399{
400 balloon_stats.target_pages = balloon_stats.current_pages;
401 return BP_ECANCELED;
402}
403#endif /* CONFIG_XEN_BALLOON_MEMORY_HOTPLUG */
404
405static long current_credit(void)
406{
407 return balloon_stats.target_pages - balloon_stats.current_pages;
408}
409
410static bool balloon_is_inflated(void)
411{
412 return balloon_stats.balloon_low || balloon_stats.balloon_high;
413}
414
415static enum bp_state increase_reservation(unsigned long nr_pages)
416{
417 int rc;
418 unsigned long i;
419 struct page *page;
420 struct xen_memory_reservation reservation = {
421 .address_bits = 0,
422 .extent_order = EXTENT_ORDER,
423 .domid = DOMID_SELF
424 };
425
426 if (nr_pages > ARRAY_SIZE(frame_list))
427 nr_pages = ARRAY_SIZE(frame_list);
428
429 page = list_first_entry_or_null(&ballooned_pages, struct page, lru);
430 for (i = 0; i < nr_pages; i++) {
431 if (!page) {
432 nr_pages = i;
433 break;
434 }
435
436 /* XENMEM_populate_physmap requires a PFN based on Xen
437 * granularity.
438 */
439 frame_list[i] = page_to_xen_pfn(page);
440 page = balloon_next_page(page);
441 }
442
443 set_xen_guest_handle(reservation.extent_start, frame_list);
444 reservation.nr_extents = nr_pages;
445 rc = HYPERVISOR_memory_op(XENMEM_populate_physmap, &reservation);
446 if (rc <= 0)
447 return BP_EAGAIN;
448
449 for (i = 0; i < rc; i++) {
450 page = balloon_retrieve(false);
451 BUG_ON(page == NULL);
452
453#ifdef CONFIG_XEN_HAVE_PVMMU
454 /*
455 * We don't support PV MMU when Linux and Xen is using
456 * different page granularity.
457 */
458 BUILD_BUG_ON(XEN_PAGE_SIZE != PAGE_SIZE);
459
460 if (!xen_feature(XENFEAT_auto_translated_physmap)) {
461 unsigned long pfn = page_to_pfn(page);
462
463 set_phys_to_machine(pfn, frame_list[i]);
464
465 /* Link back into the page tables if not highmem. */
466 if (!PageHighMem(page)) {
467 int ret;
468 ret = HYPERVISOR_update_va_mapping(
469 (unsigned long)__va(pfn << PAGE_SHIFT),
470 mfn_pte(frame_list[i], PAGE_KERNEL),
471 0);
472 BUG_ON(ret);
473 }
474 }
475#endif
476
477 /* Relinquish the page back to the allocator. */
478 free_reserved_page(page);
479 }
480
481 balloon_stats.current_pages += rc;
482
483 return BP_DONE;
484}
485
486static enum bp_state decrease_reservation(unsigned long nr_pages, gfp_t gfp)
487{
488 enum bp_state state = BP_DONE;
489 unsigned long i;
490 struct page *page, *tmp;
491 int ret;
492 struct xen_memory_reservation reservation = {
493 .address_bits = 0,
494 .extent_order = EXTENT_ORDER,
495 .domid = DOMID_SELF
496 };
497 LIST_HEAD(pages);
498
499 if (nr_pages > ARRAY_SIZE(frame_list))
500 nr_pages = ARRAY_SIZE(frame_list);
501
502 for (i = 0; i < nr_pages; i++) {
503 page = alloc_page(gfp);
504 if (page == NULL) {
505 nr_pages = i;
506 state = BP_EAGAIN;
507 break;
508 }
509 adjust_managed_page_count(page, -1);
510 scrub_page(page);
511 list_add(&page->lru, &pages);
512 }
513
514 /*
515 * Ensure that ballooned highmem pages don't have kmaps.
516 *
517 * Do this before changing the p2m as kmap_flush_unused()
518 * reads PTEs to obtain pages (and hence needs the original
519 * p2m entry).
520 */
521 kmap_flush_unused();
522
523 /*
524 * Setup the frame, update direct mapping, invalidate P2M,
525 * and add to balloon.
526 */
527 i = 0;
528 list_for_each_entry_safe(page, tmp, &pages, lru) {
529 /* XENMEM_decrease_reservation requires a GFN */
530 frame_list[i++] = xen_page_to_gfn(page);
531
532#ifdef CONFIG_XEN_HAVE_PVMMU
533 /*
534 * We don't support PV MMU when Linux and Xen is using
535 * different page granularity.
536 */
537 BUILD_BUG_ON(XEN_PAGE_SIZE != PAGE_SIZE);
538
539 if (!xen_feature(XENFEAT_auto_translated_physmap)) {
540 unsigned long pfn = page_to_pfn(page);
541
542 if (!PageHighMem(page)) {
543 ret = HYPERVISOR_update_va_mapping(
544 (unsigned long)__va(pfn << PAGE_SHIFT),
545 __pte_ma(0), 0);
546 BUG_ON(ret);
547 }
548 __set_phys_to_machine(pfn, INVALID_P2M_ENTRY);
549 }
550#endif
551 list_del(&page->lru);
552
553 balloon_append(page);
554 }
555
556 flush_tlb_all();
557
558 set_xen_guest_handle(reservation.extent_start, frame_list);
559 reservation.nr_extents = nr_pages;
560 ret = HYPERVISOR_memory_op(XENMEM_decrease_reservation, &reservation);
561 BUG_ON(ret != nr_pages);
562
563 balloon_stats.current_pages -= nr_pages;
564
565 return state;
566}
567
568/*
569 * As this is a work item it is guaranteed to run as a single instance only.
570 * We may of course race updates of the target counts (which are protected
571 * by the balloon lock), or with changes to the Xen hard limit, but we will
572 * recover from these in time.
573 */
574static void balloon_process(struct work_struct *work)
575{
576 enum bp_state state = BP_DONE;
577 long credit;
578
579
580 do {
581 mutex_lock(&balloon_mutex);
582
583 credit = current_credit();
584
585 if (credit > 0) {
586 if (balloon_is_inflated())
587 state = increase_reservation(credit);
588 else
589 state = reserve_additional_memory();
590 }
591
592 if (credit < 0)
593 state = decrease_reservation(-credit, GFP_BALLOON);
594
595 state = update_schedule(state);
596
597 mutex_unlock(&balloon_mutex);
598
599 cond_resched();
600
601 } while (credit && state == BP_DONE);
602
603 /* Schedule more work if there is some still to be done. */
604 if (state == BP_EAGAIN)
605 schedule_delayed_work(&balloon_worker, balloon_stats.schedule_delay * HZ);
606}
607
608/* Resets the Xen limit, sets new target, and kicks off processing. */
609void balloon_set_new_target(unsigned long target)
610{
611 /* No need for lock. Not read-modify-write updates. */
612 balloon_stats.target_pages = target;
613 schedule_delayed_work(&balloon_worker, 0);
614}
615EXPORT_SYMBOL_GPL(balloon_set_new_target);
616
617static int add_ballooned_pages(int nr_pages)
618{
619 enum bp_state st;
620
621 if (xen_hotplug_unpopulated) {
622 st = reserve_additional_memory();
623 if (st != BP_ECANCELED) {
624 mutex_unlock(&balloon_mutex);
625 wait_event(balloon_wq,
626 !list_empty(&ballooned_pages));
627 mutex_lock(&balloon_mutex);
628 return 0;
629 }
630 }
631
632 st = decrease_reservation(nr_pages, GFP_USER);
633 if (st != BP_DONE)
634 return -ENOMEM;
635
636 return 0;
637}
638
639/**
640 * alloc_xenballooned_pages - get pages that have been ballooned out
641 * @nr_pages: Number of pages to get
642 * @pages: pages returned
643 * @return 0 on success, error otherwise
644 */
645int alloc_xenballooned_pages(int nr_pages, struct page **pages)
646{
647 int pgno = 0;
648 struct page *page;
649 int ret;
650
651 mutex_lock(&balloon_mutex);
652
653 balloon_stats.target_unpopulated += nr_pages;
654
655 while (pgno < nr_pages) {
656 page = balloon_retrieve(true);
657 if (page) {
658 pages[pgno++] = page;
659#ifdef CONFIG_XEN_HAVE_PVMMU
660 /*
661 * We don't support PV MMU when Linux and Xen is using
662 * different page granularity.
663 */
664 BUILD_BUG_ON(XEN_PAGE_SIZE != PAGE_SIZE);
665
666 ret = xen_alloc_p2m_entry(page_to_pfn(page));
667 if (ret < 0)
668 goto out_undo;
669#endif
670 } else {
671 ret = add_ballooned_pages(nr_pages - pgno);
672 if (ret < 0)
673 goto out_undo;
674 }
675 }
676 mutex_unlock(&balloon_mutex);
677 return 0;
678 out_undo:
679 mutex_unlock(&balloon_mutex);
680 free_xenballooned_pages(pgno, pages);
681 return ret;
682}
683EXPORT_SYMBOL(alloc_xenballooned_pages);
684
685/**
686 * free_xenballooned_pages - return pages retrieved with get_ballooned_pages
687 * @nr_pages: Number of pages
688 * @pages: pages to return
689 */
690void free_xenballooned_pages(int nr_pages, struct page **pages)
691{
692 int i;
693
694 mutex_lock(&balloon_mutex);
695
696 for (i = 0; i < nr_pages; i++) {
697 if (pages[i])
698 balloon_append(pages[i]);
699 }
700
701 balloon_stats.target_unpopulated -= nr_pages;
702
703 /* The balloon may be too large now. Shrink it if needed. */
704 if (current_credit())
705 schedule_delayed_work(&balloon_worker, 0);
706
707 mutex_unlock(&balloon_mutex);
708}
709EXPORT_SYMBOL(free_xenballooned_pages);
710
711static void __init balloon_add_region(unsigned long start_pfn,
712 unsigned long pages)
713{
714 unsigned long pfn, extra_pfn_end;
715 struct page *page;
716
717 /*
718 * If the amount of usable memory has been limited (e.g., with
719 * the 'mem' command line parameter), don't add pages beyond
720 * this limit.
721 */
722 extra_pfn_end = min(max_pfn, start_pfn + pages);
723
724 for (pfn = start_pfn; pfn < extra_pfn_end; pfn++) {
725 page = pfn_to_page(pfn);
726 /* totalram_pages and totalhigh_pages do not
727 include the boot-time balloon extension, so
728 don't subtract from it. */
729 __balloon_append(page);
730 }
731
732 balloon_stats.total_pages += extra_pfn_end - start_pfn;
733}
734
735static int __init balloon_init(void)
736{
737 int i;
738
739 if (!xen_domain())
740 return -ENODEV;
741
742 pr_info("Initialising balloon driver\n");
743
744 balloon_stats.current_pages = xen_pv_domain()
745 ? min(xen_start_info->nr_pages - xen_released_pages, max_pfn)
746 : get_num_physpages();
747 balloon_stats.target_pages = balloon_stats.current_pages;
748 balloon_stats.balloon_low = 0;
749 balloon_stats.balloon_high = 0;
750 balloon_stats.total_pages = balloon_stats.current_pages;
751
752 balloon_stats.schedule_delay = 1;
753 balloon_stats.max_schedule_delay = 32;
754 balloon_stats.retry_count = 1;
755 balloon_stats.max_retry_count = RETRY_UNLIMITED;
756
757#ifdef CONFIG_XEN_BALLOON_MEMORY_HOTPLUG
758 set_online_page_callback(&xen_online_page);
759 register_memory_notifier(&xen_memory_nb);
760 register_sysctl_table(xen_root);
761#endif
762
763 /*
764 * Initialize the balloon with pages from the extra memory
765 * regions (see arch/x86/xen/setup.c).
766 */
767 for (i = 0; i < XEN_EXTRA_MEM_MAX_REGIONS; i++)
768 if (xen_extra_mem[i].n_pfns)
769 balloon_add_region(xen_extra_mem[i].start_pfn,
770 xen_extra_mem[i].n_pfns);
771
772 return 0;
773}
774subsys_initcall(balloon_init);