drivers/xen/balloon.c

   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/module.h>
  46 #include <linux/mm.h>
  47 #include <linux/bootmem.h>
  48 #include <linux/pagemap.h>
  49 #include <linux/highmem.h>
  50 #include <linux/mutex.h>
  51 #include <linux/list.h>
  52 #include <linux/gfp.h>
  53 #include <linux/notifier.h>
  54 #include <linux/memory.h>
  55 #include <linux/memory_hotplug.h>
  56 #include <linux/percpu-defs.h>
  57 #include <linux/slab.h>
  58 #include <linux/sysctl.h>
  59
  60 #include <asm/page.h>
  61 #include <asm/pgalloc.h>
  62 #include <asm/pgtable.h>
  63 #include <asm/tlb.h>
  64
  65 #include <asm/xen/hypervisor.h>
  66 #include <asm/xen/hypercall.h>
  67
  68 #include <xen/xen.h>
  69 #include <xen/interface/xen.h>
  70 #include <xen/interface/memory.h>
  71 #include <xen/balloon.h>
  72 #include <xen/features.h>
  73 #include <xen/page.h>
  74
  75 static int xen_hotplug_unpopulated;
  76
  77 #ifdef CONFIG_XEN_BALLOON_MEMORY_HOTPLUG
  78
  79 static int zero;
  80 static int one = 1;
  81
  82 static struct ctl_table balloon_table[] = {
  83         {
  84                 .procname       = "hotplug_unpopulated",
  85                 .data           = &xen_hotplug_unpopulated,
  86                 .maxlen         = sizeof(int),
  87                 .mode           = 0644,
  88                 .proc_handler   = proc_dointvec_minmax,
  89                 .extra1         = &zero,
  90                 .extra2         = &one,
  91         },
  92         { }
  93 };
  94
  95 static struct ctl_table balloon_root[] = {
  96         {
  97                 .procname       = "balloon",
  98                 .mode           = 0555,
  99                 .child          = balloon_table,
 100         },
 101         { }
 102 };
 103
 104 static struct ctl_table xen_root[] = {
 105         {
 106                 .procname       = "xen",
 107                 .mode           = 0555,
 108                 .child          = balloon_root,
 109         },
 110         { }
 111 };
 112
 113 #endif
 114
 115 /*
 116  * balloon_process() state:
 117  *
 118  * BP_DONE: done or nothing to do,
 119  * BP_WAIT: wait to be rescheduled,
 120  * BP_EAGAIN: error, go to sleep,
 121  * BP_ECANCELED: error, balloon operation canceled.
 122  */
 123
 124 enum bp_state {
 125         BP_DONE,
 126         BP_WAIT,
 127         BP_EAGAIN,
 128         BP_ECANCELED
 129 };
 130
 131
 132 static DEFINE_MUTEX(balloon_mutex);
 133
 134 struct balloon_stats balloon_stats;
 135 EXPORT_SYMBOL_GPL(balloon_stats);
 136
 137 /* We increase/decrease in batches which fit in a page */
 138 static xen_pfn_t frame_list[PAGE_SIZE / sizeof(unsigned long)];
 139
 140
 141 /* List of ballooned pages, threaded through the mem_map array. */
 142 static LIST_HEAD(ballooned_pages);
 143 static DECLARE_WAIT_QUEUE_HEAD(balloon_wq);
 144
 145 /* Main work function, always executed in process context. */
 146 static void balloon_process(struct work_struct *work);
 147 static DECLARE_DELAYED_WORK(balloon_worker, balloon_process);
 148
 149 /* When ballooning out (allocating memory to return to Xen) we don't really
 150    want the kernel to try too hard since that can trigger the oom killer. */
 151 #define GFP_BALLOON \
 152         (GFP_HIGHUSER | __GFP_NOWARN | __GFP_NORETRY | __GFP_NOMEMALLOC)
 153
 154 static void scrub_page(struct page *page)
 155 {
 156 #ifdef CONFIG_XEN_SCRUB_PAGES
 157         clear_highpage(page);
 158 #endif
 159 }
 160
 161 /* balloon_append: add the given page to the balloon. */
 162 static void __balloon_append(struct page *page)
 163 {
 164         /* Lowmem is re-populated first, so highmem pages go at list tail. */
 165         if (PageHighMem(page)) {
 166                 list_add_tail(&page->lru, &ballooned_pages);
 167                 balloon_stats.balloon_high++;
 168         } else {
 169                 list_add(&page->lru, &ballooned_pages);
 170                 balloon_stats.balloon_low++;
 171         }
 172         wake_up(&balloon_wq);
 173 }
 174
 175 static void balloon_append(struct page *page)
 176 {
 177         __balloon_append(page);
 178         adjust_managed_page_count(page, -1);
 179 }
 180
 181 /* balloon_retrieve: rescue a page from the balloon, if it is not empty. */
 182 static struct page *balloon_retrieve(bool require_lowmem)
 183 {
 184         struct page *page;
 185
 186         if (list_empty(&ballooned_pages))
 187                 return NULL;
 188
 189         page = list_entry(ballooned_pages.next, struct page, lru);
 190         if (require_lowmem && PageHighMem(page))
 191                 return NULL;
 192         list_del(&page->lru);
 193
 194         if (PageHighMem(page))
 195                 balloon_stats.balloon_high--;
 196         else
 197                 balloon_stats.balloon_low--;
 198
 199         adjust_managed_page_count(page, 1);
 200
 201         return page;
 202 }
 203
 204 static struct page *balloon_next_page(struct page *page)
 205 {
 206         struct list_head *next = page->lru.next;
 207         if (next == &ballooned_pages)
 208                 return NULL;
 209         return list_entry(next, struct page, lru);
 210 }
 211
 212 static enum bp_state update_schedule(enum bp_state state)
 213 {
 214         if (state == BP_WAIT)
 215                 return BP_WAIT;
 216
 217         if (state == BP_ECANCELED)
 218                 return BP_ECANCELED;
 219
 220         if (state == BP_DONE) {
 221                 balloon_stats.schedule_delay = 1;
 222                 balloon_stats.retry_count = 1;
 223                 return BP_DONE;
 224         }
 225
 226         ++balloon_stats.retry_count;
 227
 228         if (balloon_stats.max_retry_count != RETRY_UNLIMITED &&
 229                         balloon_stats.retry_count > balloon_stats.max_retry_count) {
 230                 balloon_stats.schedule_delay = 1;
 231                 balloon_stats.retry_count = 1;
 232                 return BP_ECANCELED;
 233         }
 234
 235         balloon_stats.schedule_delay <<= 1;
 236
 237         if (balloon_stats.schedule_delay > balloon_stats.max_schedule_delay)
 238                 balloon_stats.schedule_delay = balloon_stats.max_schedule_delay;
 239
 240         return BP_EAGAIN;
 241 }
 242
 243 #ifdef CONFIG_XEN_BALLOON_MEMORY_HOTPLUG
 244 static struct resource *additional_memory_resource(phys_addr_t size)
 245 {
 246         struct resource *res;
 247         int ret;
 248
 249         res = kzalloc(sizeof(*res), GFP_KERNEL);
 250         if (!res)
 251                 return NULL;
 252
 253         res->name = "System RAM";
 254         res->flags = IORESOURCE_MEM | IORESOURCE_BUSY;
 255
 256         ret = allocate_resource(&iomem_resource, res,
 257                                 size, 0, -1,
 258                                 PAGES_PER_SECTION * PAGE_SIZE, NULL, NULL);
 259         if (ret < 0) {
 260                 pr_err("Cannot allocate new System RAM resource\n");
 261                 kfree(res);
 262                 return NULL;
 263         }
 264
 265         return res;
 266 }
 267
 268 static void release_memory_resource(struct resource *resource)
 269 {
 270         if (!resource)
 271                 return;
 272
 273         /*
 274          * No need to reset region to identity mapped since we now
 275          * know that no I/O can be in this region
 276          */
 277         release_resource(resource);
 278         kfree(resource);
 279 }
 280
 281 static enum bp_state reserve_additional_memory(void)
 282 {
 283         long credit;
 284         struct resource *resource;
 285         int nid, rc;
 286         unsigned long balloon_hotplug;
 287
 288         credit = balloon_stats.target_pages + balloon_stats.target_unpopulated
 289                 - balloon_stats.total_pages;
 290
 291         /*
 292          * Already hotplugged enough pages?  Wait for them to be
 293          * onlined.
 294          */
 295         if (credit <= 0)
 296                 return BP_WAIT;
 297
 298         balloon_hotplug = round_up(credit, PAGES_PER_SECTION);
 299
 300         resource = additional_memory_resource(balloon_hotplug * PAGE_SIZE);
 301         if (!resource)
 302                 goto err;
 303
 304         nid = memory_add_physaddr_to_nid(resource->start);
 305
 306 #ifdef CONFIG_XEN_HAVE_PVMMU
 307         /*
 308          * add_memory() will build page tables for the new memory so
 309          * the p2m must contain invalid entries so the correct
 310          * non-present PTEs will be written.
 311          *
 312          * If a failure occurs, the original (identity) p2m entries
 313          * are not restored since this region is now known not to
 314          * conflict with any devices.
 315          */
 316         if (!xen_feature(XENFEAT_auto_translated_physmap)) {
 317                 unsigned long pfn, i;
 318
 319                 pfn = PFN_DOWN(resource->start);
 320                 for (i = 0; i < balloon_hotplug; i++) {
 321                         if (!set_phys_to_machine(pfn + i, INVALID_P2M_ENTRY)) {
 322                                 pr_warn("set_phys_to_machine() failed, no memory added\n");
 323                                 goto err;
 324                         }
 325                 }
 326         }
 327 #endif
 328
 329         rc = add_memory_resource(nid, resource);
 330         if (rc) {
 331                 pr_warn("Cannot add additional memory (%i)\n", rc);
 332                 goto err;
 333         }
 334
 335         balloon_stats.total_pages += balloon_hotplug;
 336
 337         return BP_WAIT;
 338   err:
 339         release_memory_resource(resource);
 340         return BP_ECANCELED;
 341 }
 342
 343 static void xen_online_page(struct page *page)
 344 {
 345         __online_page_set_limits(page);
 346
 347         mutex_lock(&balloon_mutex);
 348
 349         __balloon_append(page);
 350
 351         mutex_unlock(&balloon_mutex);
 352 }
 353
 354 static int xen_memory_notifier(struct notifier_block *nb, unsigned long val, void *v)
 355 {
 356         if (val == MEM_ONLINE)
 357                 schedule_delayed_work(&balloon_worker, 0);
 358
 359         return NOTIFY_OK;
 360 }
 361
 362 static struct notifier_block xen_memory_nb = {
 363         .notifier_call = xen_memory_notifier,
 364         .priority = 0
 365 };
 366 #else
 367 static enum bp_state reserve_additional_memory(void)
 368 {
 369         balloon_stats.target_pages = balloon_stats.current_pages;
 370         return BP_ECANCELED;
 371 }
 372 #endif /* CONFIG_XEN_BALLOON_MEMORY_HOTPLUG */
 373
 374 static long current_credit(void)
 375 {
 376         return balloon_stats.target_pages - balloon_stats.current_pages;
 377 }
 378
 379 static bool balloon_is_inflated(void)
 380 {
 381         return balloon_stats.balloon_low || balloon_stats.balloon_high;
 382 }
 383
 384 static enum bp_state increase_reservation(unsigned long nr_pages)
 385 {
 386         int rc;
 387         unsigned long  pfn, i;
 388         struct page   *page;
 389         struct xen_memory_reservation reservation = {
 390                 .address_bits = 0,
 391                 .extent_order = 0,
 392                 .domid        = DOMID_SELF
 393         };
 394
 395         if (nr_pages > ARRAY_SIZE(frame_list))
 396                 nr_pages = ARRAY_SIZE(frame_list);
 397
 398         page = list_first_entry_or_null(&ballooned_pages, struct page, lru);
 399         for (i = 0; i < nr_pages; i++) {
 400                 if (!page) {
 401                         nr_pages = i;
 402                         break;
 403                 }
 404                 frame_list[i] = page_to_pfn(page);
 405                 page = balloon_next_page(page);
 406         }
 407
 408         set_xen_guest_handle(reservation.extent_start, frame_list);
 409         reservation.nr_extents = nr_pages;
 410         rc = HYPERVISOR_memory_op(XENMEM_populate_physmap, &reservation);
 411         if (rc <= 0)
 412                 return BP_EAGAIN;
 413
 414         for (i = 0; i < rc; i++) {
 415                 page = balloon_retrieve(false);
 416                 BUG_ON(page == NULL);
 417
 418                 pfn = page_to_pfn(page);
 419
 420 #ifdef CONFIG_XEN_HAVE_PVMMU
 421                 if (!xen_feature(XENFEAT_auto_translated_physmap)) {
 422                         set_phys_to_machine(pfn, frame_list[i]);
 423
 424                         /* Link back into the page tables if not highmem. */
 425                         if (!PageHighMem(page)) {
 426                                 int ret;
 427                                 ret = HYPERVISOR_update_va_mapping(
 428                                                 (unsigned long)__va(pfn << PAGE_SHIFT),
 429                                                 mfn_pte(frame_list[i], PAGE_KERNEL),
 430                                                 0);
 431                                 BUG_ON(ret);
 432                         }
 433                 }
 434 #endif
 435
 436                 /* Relinquish the page back to the allocator. */
 437                 __free_reserved_page(page);
 438         }
 439
 440         balloon_stats.current_pages += rc;
 441
 442         return BP_DONE;
 443 }
 444
 445 static enum bp_state decrease_reservation(unsigned long nr_pages, gfp_t gfp)
 446 {
 447         enum bp_state state = BP_DONE;
 448         unsigned long  pfn, i;
 449         struct page   *page;
 450         int ret;
 451         struct xen_memory_reservation reservation = {
 452                 .address_bits = 0,
 453                 .extent_order = 0,
 454                 .domid        = DOMID_SELF
 455         };
 456
 457         if (nr_pages > ARRAY_SIZE(frame_list))
 458                 nr_pages = ARRAY_SIZE(frame_list);
 459
 460         for (i = 0; i < nr_pages; i++) {
 461                 page = alloc_page(gfp);
 462                 if (page == NULL) {
 463                         nr_pages = i;
 464                         state = BP_EAGAIN;
 465                         break;
 466                 }
 467                 scrub_page(page);
 468
 469                 frame_list[i] = page_to_pfn(page);
 470         }
 471
 472         /*
 473          * Ensure that ballooned highmem pages don't have kmaps.
 474          *
 475          * Do this before changing the p2m as kmap_flush_unused()
 476          * reads PTEs to obtain pages (and hence needs the original
 477          * p2m entry).
 478          */
 479         kmap_flush_unused();
 480
 481         /* Update direct mapping, invalidate P2M, and add to balloon. */
 482         for (i = 0; i < nr_pages; i++) {
 483                 pfn = frame_list[i];
 484                 frame_list[i] = pfn_to_gfn(pfn);
 485                 page = pfn_to_page(pfn);
 486
 487 #ifdef CONFIG_XEN_HAVE_PVMMU
 488                 if (!xen_feature(XENFEAT_auto_translated_physmap)) {
 489                         if (!PageHighMem(page)) {
 490                                 ret = HYPERVISOR_update_va_mapping(
 491                                                 (unsigned long)__va(pfn << PAGE_SHIFT),
 492                                                 __pte_ma(0), 0);
 493                                 BUG_ON(ret);
 494                         }
 495                         __set_phys_to_machine(pfn, INVALID_P2M_ENTRY);
 496                 }
 497 #endif
 498
 499                 balloon_append(page);
 500         }
 501
 502         flush_tlb_all();
 503
 504         set_xen_guest_handle(reservation.extent_start, frame_list);
 505         reservation.nr_extents   = nr_pages;
 506         ret = HYPERVISOR_memory_op(XENMEM_decrease_reservation, &reservation);
 507         BUG_ON(ret != nr_pages);
 508
 509         balloon_stats.current_pages -= nr_pages;
 510
 511         return state;
 512 }
 513
 514 /*
 515  * As this is a work item it is guaranteed to run as a single instance only.
 516  * We may of course race updates of the target counts (which are protected
 517  * by the balloon lock), or with changes to the Xen hard limit, but we will
 518  * recover from these in time.
 519  */
 520 static void balloon_process(struct work_struct *work)
 521 {
 522         enum bp_state state = BP_DONE;
 523         long credit;
 524
 525
 526         do {
 527                 mutex_lock(&balloon_mutex);
 528
 529                 credit = current_credit();
 530
 531                 if (credit > 0) {
 532                         if (balloon_is_inflated())
 533                                 state = increase_reservation(credit);
 534                         else
 535                                 state = reserve_additional_memory();
 536                 }
 537
 538                 if (credit < 0)
 539                         state = decrease_reservation(-credit, GFP_BALLOON);
 540
 541                 state = update_schedule(state);
 542
 543                 mutex_unlock(&balloon_mutex);
 544
 545                 cond_resched();
 546
 547         } while (credit && state == BP_DONE);
 548
 549         /* Schedule more work if there is some still to be done. */
 550         if (state == BP_EAGAIN)
 551                 schedule_delayed_work(&balloon_worker, balloon_stats.schedule_delay * HZ);
 552 }
 553
 554 /* Resets the Xen limit, sets new target, and kicks off processing. */
 555 void balloon_set_new_target(unsigned long target)
 556 {
 557         /* No need for lock. Not read-modify-write updates. */
 558         balloon_stats.target_pages = target;
 559         schedule_delayed_work(&balloon_worker, 0);
 560 }
 561 EXPORT_SYMBOL_GPL(balloon_set_new_target);
 562
 563 static int add_ballooned_pages(int nr_pages)
 564 {
 565         enum bp_state st;
 566
 567         if (xen_hotplug_unpopulated) {
 568                 st = reserve_additional_memory();
 569                 if (st != BP_ECANCELED) {
 570                         mutex_unlock(&balloon_mutex);
 571                         wait_event(balloon_wq,
 572                                    !list_empty(&ballooned_pages));
 573                         mutex_lock(&balloon_mutex);
 574                         return 0;
 575                 }
 576         }
 577
 578         st = decrease_reservation(nr_pages, GFP_USER);
 579         if (st != BP_DONE)
 580                 return -ENOMEM;
 581
 582         return 0;
 583 }
 584
 585 /**
 586  * alloc_xenballooned_pages - get pages that have been ballooned out
 587  * @nr_pages: Number of pages to get
 588  * @pages: pages returned
 589  * @return 0 on success, error otherwise
 590  */
 591 int alloc_xenballooned_pages(int nr_pages, struct page **pages)
 592 {
 593         int pgno = 0;
 594         struct page *page;
 595         int ret;
 596
 597         mutex_lock(&balloon_mutex);
 598
 599         balloon_stats.target_unpopulated += nr_pages;
 600
 601         while (pgno < nr_pages) {
 602                 page = balloon_retrieve(true);
 603                 if (page) {
 604                         pages[pgno++] = page;
 605                 } else {
 606                         ret = add_ballooned_pages(nr_pages - pgno);
 607                         if (ret < 0)
 608                                 goto out_undo;
 609                 }
 610         }
 611         mutex_unlock(&balloon_mutex);
 612         return 0;
 613  out_undo:
 614         mutex_unlock(&balloon_mutex);
 615         free_xenballooned_pages(pgno, pages);
 616         return ret;
 617 }
 618 EXPORT_SYMBOL(alloc_xenballooned_pages);
 619
 620 /**
 621  * free_xenballooned_pages - return pages retrieved with get_ballooned_pages
 622  * @nr_pages: Number of pages
 623  * @pages: pages to return
 624  */
 625 void free_xenballooned_pages(int nr_pages, struct page **pages)
 626 {
 627         int i;
 628
 629         mutex_lock(&balloon_mutex);
 630
 631         for (i = 0; i < nr_pages; i++) {
 632                 if (pages[i])
 633                         balloon_append(pages[i]);
 634         }
 635
 636         balloon_stats.target_unpopulated -= nr_pages;
 637
 638         /* The balloon may be too large now. Shrink it if needed. */
 639         if (current_credit())
 640                 schedule_delayed_work(&balloon_worker, 0);
 641
 642         mutex_unlock(&balloon_mutex);
 643 }
 644 EXPORT_SYMBOL(free_xenballooned_pages);
 645
 646 static void __init balloon_add_region(unsigned long start_pfn,
 647                                       unsigned long pages)
 648 {
 649         unsigned long pfn, extra_pfn_end;
 650         struct page *page;
 651
 652         /*
 653          * If the amount of usable memory has been limited (e.g., with
 654          * the 'mem' command line parameter), don't add pages beyond
 655          * this limit.
 656          */
 657         extra_pfn_end = min(max_pfn, start_pfn + pages);
 658
 659         for (pfn = start_pfn; pfn < extra_pfn_end; pfn++) {
 660                 page = pfn_to_page(pfn);
 661                 /* totalram_pages and totalhigh_pages do not
 662                    include the boot-time balloon extension, so
 663                    don't subtract from it. */
 664                 __balloon_append(page);
 665         }
 666
 667         balloon_stats.total_pages += extra_pfn_end - start_pfn;
 668 }
 669
 670 static int __init balloon_init(void)
 671 {
 672         int i;
 673
 674         if (!xen_domain())
 675                 return -ENODEV;
 676
 677         pr_info("Initialising balloon driver\n");
 678
 679         balloon_stats.current_pages = xen_pv_domain()
 680                 ? min(xen_start_info->nr_pages - xen_released_pages, max_pfn)
 681                 : get_num_physpages();
 682         balloon_stats.target_pages  = balloon_stats.current_pages;
 683         balloon_stats.balloon_low   = 0;
 684         balloon_stats.balloon_high  = 0;
 685         balloon_stats.total_pages   = balloon_stats.current_pages;
 686
 687         balloon_stats.schedule_delay = 1;
 688         balloon_stats.max_schedule_delay = 32;
 689         balloon_stats.retry_count = 1;
 690         balloon_stats.max_retry_count = RETRY_UNLIMITED;
 691
 692 #ifdef CONFIG_XEN_BALLOON_MEMORY_HOTPLUG
 693         set_online_page_callback(&xen_online_page);
 694         register_memory_notifier(&xen_memory_nb);
 695         register_sysctl_table(xen_root);
 696 #endif
 697
 698         /*
 699          * Initialize the balloon with pages from the extra memory
 700          * regions (see arch/x86/xen/setup.c).
 701          */
 702         for (i = 0; i < XEN_EXTRA_MEM_MAX_REGIONS; i++)
 703                 if (xen_extra_mem[i].n_pfns)
 704                         balloon_add_region(xen_extra_mem[i].start_pfn,
 705                                            xen_extra_mem[i].n_pfns);
 706
 707         return 0;
 708 }
 709
 710 subsys_initcall(balloon_init);
 711
 712 MODULE_LICENSE("GPL");