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/cred.h>
  45 #include <linux/errno.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 #include <xen/mem-reservation.h>
  75
  76 static int xen_hotplug_unpopulated;
  77
  78 #ifdef CONFIG_XEN_BALLOON_MEMORY_HOTPLUG
  79
  80 static int zero;
  81 static int one = 1;
  82
  83 static struct ctl_table balloon_table[] = {
  84         {
  85                 .procname       = "hotplug_unpopulated",
  86                 .data           = &xen_hotplug_unpopulated,
  87                 .maxlen         = sizeof(int),
  88                 .mode           = 0644,
  89                 .proc_handler   = proc_dointvec_minmax,
  90                 .extra1         = &zero,
  91                 .extra2         = &one,
  92         },
  93         { }
  94 };
  95
  96 static struct ctl_table balloon_root[] = {
  97         {
  98                 .procname       = "balloon",
  99                 .mode           = 0555,
 100                 .child          = balloon_table,
 101         },
 102         { }
 103 };
 104
 105 static struct ctl_table xen_root[] = {
 106         {
 107                 .procname       = "xen",
 108                 .mode           = 0555,
 109                 .child          = balloon_root,
 110         },
 111         { }
 112 };
 113
 114 #endif
 115
 116 /*
 117  * Use one extent per PAGE_SIZE to avoid to break down the page into
 118  * multiple frame.
 119  */
 120 #define EXTENT_ORDER (fls(XEN_PFN_PER_PAGE) - 1)
 121
 122 /*
 123  * balloon_process() state:
 124  *
 125  * BP_DONE: done or nothing to do,
 126  * BP_WAIT: wait to be rescheduled,
 127  * BP_EAGAIN: error, go to sleep,
 128  * BP_ECANCELED: error, balloon operation canceled.
 129  */
 130
 131 enum bp_state {
 132         BP_DONE,
 133         BP_WAIT,
 134         BP_EAGAIN,
 135         BP_ECANCELED
 136 };
 137
 138
 139 static DEFINE_MUTEX(balloon_mutex);
 140
 141 struct balloon_stats balloon_stats;
 142 EXPORT_SYMBOL_GPL(balloon_stats);
 143
 144 /* We increase/decrease in batches which fit in a page */
 145 static xen_pfn_t frame_list[PAGE_SIZE / sizeof(xen_pfn_t)];
 146
 147
 148 /* List of ballooned pages, threaded through the mem_map array. */
 149 static LIST_HEAD(ballooned_pages);
 150 static DECLARE_WAIT_QUEUE_HEAD(balloon_wq);
 151
 152 /* Main work function, always executed in process context. */
 153 static void balloon_process(struct work_struct *work);
 154 static DECLARE_DELAYED_WORK(balloon_worker, balloon_process);
 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 /* 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 }
 179
 180 /* balloon_retrieve: rescue a page from the balloon, if it is not empty. */
 181 static struct page *balloon_retrieve(bool require_lowmem)
 182 {
 183         struct page *page;
 184
 185         if (list_empty(&ballooned_pages))
 186                 return NULL;
 187
 188         page = list_entry(ballooned_pages.next, struct page, lru);
 189         if (require_lowmem && PageHighMem(page))
 190                 return NULL;
 191         list_del(&page->lru);
 192
 193         if (PageHighMem(page))
 194                 balloon_stats.balloon_high--;
 195         else
 196                 balloon_stats.balloon_low--;
 197
 198         return page;
 199 }
 200
 201 static struct page *balloon_next_page(struct page *page)
 202 {
 203         struct list_head *next = page->lru.next;
 204         if (next == &ballooned_pages)
 205                 return NULL;
 206         return list_entry(next, struct page, lru);
 207 }
 208
 209 static enum bp_state update_schedule(enum bp_state state)
 210 {
 211         if (state == BP_WAIT)
 212                 return BP_WAIT;
 213
 214         if (state == BP_ECANCELED)
 215                 return BP_ECANCELED;
 216
 217         if (state == BP_DONE) {
 218                 balloon_stats.schedule_delay = 1;
 219                 balloon_stats.retry_count = 1;
 220                 return BP_DONE;
 221         }
 222
 223         ++balloon_stats.retry_count;
 224
 225         if (balloon_stats.max_retry_count != RETRY_UNLIMITED &&
 226                         balloon_stats.retry_count > balloon_stats.max_retry_count) {
 227                 balloon_stats.schedule_delay = 1;
 228                 balloon_stats.retry_count = 1;
 229                 return BP_ECANCELED;
 230         }
 231
 232         balloon_stats.schedule_delay <<= 1;
 233
 234         if (balloon_stats.schedule_delay > balloon_stats.max_schedule_delay)
 235                 balloon_stats.schedule_delay = balloon_stats.max_schedule_delay;
 236
 237         return BP_EAGAIN;
 238 }
 239
 240 #ifdef CONFIG_XEN_BALLOON_MEMORY_HOTPLUG
 241 static void release_memory_resource(struct resource *resource)
 242 {
 243         if (!resource)
 244                 return;
 245
 246         /*
 247          * No need to reset region to identity mapped since we now
 248          * know that no I/O can be in this region
 249          */
 250         release_resource(resource);
 251         kfree(resource);
 252 }
 253
 254 static struct resource *additional_memory_resource(phys_addr_t size)
 255 {
 256         struct resource *res;
 257         int ret;
 258
 259         res = kzalloc(sizeof(*res), GFP_KERNEL);
 260         if (!res)
 261                 return NULL;
 262
 263         res->name = "System RAM";
 264         res->flags = IORESOURCE_SYSTEM_RAM | IORESOURCE_BUSY;
 265
 266         ret = allocate_resource(&iomem_resource, res,
 267                                 size, 0, -1,
 268                                 PAGES_PER_SECTION * PAGE_SIZE, NULL, NULL);
 269         if (ret < 0) {
 270                 pr_err("Cannot allocate new System RAM resource\n");
 271                 kfree(res);
 272                 return NULL;
 273         }
 274
 275 #ifdef CONFIG_SPARSEMEM
 276         {
 277                 unsigned long limit = 1UL << (MAX_PHYSMEM_BITS - PAGE_SHIFT);
 278                 unsigned long pfn = res->start >> PAGE_SHIFT;
 279
 280                 if (pfn > limit) {
 281                         pr_err("New System RAM resource outside addressable RAM (%lu > %lu)\n",
 282                                pfn, limit);
 283                         release_memory_resource(res);
 284                         return NULL;
 285                 }
 286         }
 287 #endif
 288
 289         return res;
 290 }
 291
 292 static enum bp_state reserve_additional_memory(void)
 293 {
 294         long credit;
 295         struct resource *resource;
 296         int nid, rc;
 297         unsigned long balloon_hotplug;
 298
 299         credit = balloon_stats.target_pages + balloon_stats.target_unpopulated
 300                 - balloon_stats.total_pages;
 301
 302         /*
 303          * Already hotplugged enough pages?  Wait for them to be
 304          * onlined.
 305          */
 306         if (credit <= 0)
 307                 return BP_WAIT;
 308
 309         balloon_hotplug = round_up(credit, PAGES_PER_SECTION);
 310
 311         resource = additional_memory_resource(balloon_hotplug * PAGE_SIZE);
 312         if (!resource)
 313                 goto err;
 314
 315         nid = memory_add_physaddr_to_nid(resource->start);
 316
 317 #ifdef CONFIG_XEN_HAVE_PVMMU
 318         /*
 319          * We don't support PV MMU when Linux and Xen is using
 320          * different page granularity.
 321          */
 322         BUILD_BUG_ON(XEN_PAGE_SIZE != PAGE_SIZE);
 323
 324         /*
 325          * add_memory() will build page tables for the new memory so
 326          * the p2m must contain invalid entries so the correct
 327          * non-present PTEs will be written.
 328          *
 329          * If a failure occurs, the original (identity) p2m entries
 330          * are not restored since this region is now known not to
 331          * conflict with any devices.
 332          */
 333         if (!xen_feature(XENFEAT_auto_translated_physmap)) {
 334                 unsigned long pfn, i;
 335
 336                 pfn = PFN_DOWN(resource->start);
 337                 for (i = 0; i < balloon_hotplug; i++) {
 338                         if (!set_phys_to_machine(pfn + i, INVALID_P2M_ENTRY)) {
 339                                 pr_warn("set_phys_to_machine() failed, no memory added\n");
 340                                 goto err;
 341                         }
 342                 }
 343         }
 344 #endif
 345
 346         /*
 347          * add_memory_resource() will call online_pages() which in its turn
 348          * will call xen_online_page() callback causing deadlock if we don't
 349          * release balloon_mutex here. Unlocking here is safe because the
 350          * callers drop the mutex before trying again.
 351          */
 352         mutex_unlock(&balloon_mutex);
 353         rc = add_memory_resource(nid, resource, memhp_auto_online);
 354         mutex_lock(&balloon_mutex);
 355
 356         if (rc) {
 357                 pr_warn("Cannot add additional memory (%i)\n", rc);
 358                 goto err;
 359         }
 360
 361         balloon_stats.total_pages += balloon_hotplug;
 362
 363         return BP_WAIT;
 364   err:
 365         release_memory_resource(resource);
 366         return BP_ECANCELED;
 367 }
 368
 369 static void xen_online_page(struct page *page)
 370 {
 371         __online_page_set_limits(page);
 372
 373         mutex_lock(&balloon_mutex);
 374
 375         __balloon_append(page);
 376
 377         mutex_unlock(&balloon_mutex);
 378 }
 379
 380 static int xen_memory_notifier(struct notifier_block *nb, unsigned long val, void *v)
 381 {
 382         if (val == MEM_ONLINE)
 383                 schedule_delayed_work(&balloon_worker, 0);
 384
 385         return NOTIFY_OK;
 386 }
 387
 388 static struct notifier_block xen_memory_nb = {
 389         .notifier_call = xen_memory_notifier,
 390         .priority = 0
 391 };
 392 #else
 393 static enum bp_state reserve_additional_memory(void)
 394 {
 395         balloon_stats.target_pages = balloon_stats.current_pages;
 396         return BP_ECANCELED;
 397 }
 398 #endif /* CONFIG_XEN_BALLOON_MEMORY_HOTPLUG */
 399
 400 static long current_credit(void)
 401 {
 402         return balloon_stats.target_pages - balloon_stats.current_pages;
 403 }
 404
 405 static bool balloon_is_inflated(void)
 406 {
 407         return balloon_stats.balloon_low || balloon_stats.balloon_high;
 408 }
 409
 410 static enum bp_state increase_reservation(unsigned long nr_pages)
 411 {
 412         int rc;
 413         unsigned long i;
 414         struct page   *page;
 415
 416         if (nr_pages > ARRAY_SIZE(frame_list))
 417                 nr_pages = ARRAY_SIZE(frame_list);
 418
 419         page = list_first_entry_or_null(&ballooned_pages, struct page, lru);
 420         for (i = 0; i < nr_pages; i++) {
 421                 if (!page) {
 422                         nr_pages = i;
 423                         break;
 424                 }
 425
 426                 frame_list[i] = page_to_xen_pfn(page);
 427                 page = balloon_next_page(page);
 428         }
 429
 430         rc = xenmem_reservation_increase(nr_pages, frame_list);
 431         if (rc <= 0)
 432                 return BP_EAGAIN;
 433
 434         for (i = 0; i < rc; i++) {
 435                 page = balloon_retrieve(false);
 436                 BUG_ON(page == NULL);
 437
 438                 xenmem_reservation_va_mapping_update(1, &page, &frame_list[i]);
 439
 440                 /* Relinquish the page back to the allocator. */
 441                 free_reserved_page(page);
 442         }
 443
 444         balloon_stats.current_pages += rc;
 445
 446         return BP_DONE;
 447 }
 448
 449 static enum bp_state decrease_reservation(unsigned long nr_pages, gfp_t gfp)
 450 {
 451         enum bp_state state = BP_DONE;
 452         unsigned long i;
 453         struct page *page, *tmp;
 454         int ret;
 455         LIST_HEAD(pages);
 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                 adjust_managed_page_count(page, -1);
 468                 xenmem_reservation_scrub_page(page);
 469                 list_add(&page->lru, &pages);
 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         /*
 482          * Setup the frame, update direct mapping, invalidate P2M,
 483          * and add to balloon.
 484          */
 485         i = 0;
 486         list_for_each_entry_safe(page, tmp, &pages, lru) {
 487                 frame_list[i++] = xen_page_to_gfn(page);
 488
 489                 xenmem_reservation_va_mapping_reset(1, &page);
 490
 491                 list_del(&page->lru);
 492
 493                 balloon_append(page);
 494         }
 495
 496         flush_tlb_all();
 497
 498         ret = xenmem_reservation_decrease(nr_pages, frame_list);
 499         BUG_ON(ret != nr_pages);
 500
 501         balloon_stats.current_pages -= nr_pages;
 502
 503         return state;
 504 }
 505
 506 /*
 507  * As this is a work item it is guaranteed to run as a single instance only.
 508  * We may of course race updates of the target counts (which are protected
 509  * by the balloon lock), or with changes to the Xen hard limit, but we will
 510  * recover from these in time.
 511  */
 512 static void balloon_process(struct work_struct *work)
 513 {
 514         enum bp_state state = BP_DONE;
 515         long credit;
 516
 517
 518         do {
 519                 mutex_lock(&balloon_mutex);
 520
 521                 credit = current_credit();
 522
 523                 if (credit > 0) {
 524                         if (balloon_is_inflated())
 525                                 state = increase_reservation(credit);
 526                         else
 527                                 state = reserve_additional_memory();
 528                 }
 529
 530                 if (credit < 0)
 531                         state = decrease_reservation(-credit, GFP_BALLOON);
 532
 533                 state = update_schedule(state);
 534
 535                 mutex_unlock(&balloon_mutex);
 536
 537                 cond_resched();
 538
 539         } while (credit && state == BP_DONE);
 540
 541         /* Schedule more work if there is some still to be done. */
 542         if (state == BP_EAGAIN)
 543                 schedule_delayed_work(&balloon_worker, balloon_stats.schedule_delay * HZ);
 544 }
 545
 546 /* Resets the Xen limit, sets new target, and kicks off processing. */
 547 void balloon_set_new_target(unsigned long target)
 548 {
 549         /* No need for lock. Not read-modify-write updates. */
 550         balloon_stats.target_pages = target;
 551         schedule_delayed_work(&balloon_worker, 0);
 552 }
 553 EXPORT_SYMBOL_GPL(balloon_set_new_target);
 554
 555 static int add_ballooned_pages(int nr_pages)
 556 {
 557         enum bp_state st;
 558
 559         if (xen_hotplug_unpopulated) {
 560                 st = reserve_additional_memory();
 561                 if (st != BP_ECANCELED) {
 562                         mutex_unlock(&balloon_mutex);
 563                         wait_event(balloon_wq,
 564                                    !list_empty(&ballooned_pages));
 565                         mutex_lock(&balloon_mutex);
 566                         return 0;
 567                 }
 568         }
 569
 570         st = decrease_reservation(nr_pages, GFP_USER);
 571         if (st != BP_DONE)
 572                 return -ENOMEM;
 573
 574         return 0;
 575 }
 576
 577 /**
 578  * alloc_xenballooned_pages - get pages that have been ballooned out
 579  * @nr_pages: Number of pages to get
 580  * @pages: pages returned
 581  * @return 0 on success, error otherwise
 582  */
 583 int alloc_xenballooned_pages(int nr_pages, struct page **pages)
 584 {
 585         int pgno = 0;
 586         struct page *page;
 587         int ret;
 588
 589         mutex_lock(&balloon_mutex);
 590
 591         balloon_stats.target_unpopulated += nr_pages;
 592
 593         while (pgno < nr_pages) {
 594                 page = balloon_retrieve(true);
 595                 if (page) {
 596                         pages[pgno++] = page;
 597 #ifdef CONFIG_XEN_HAVE_PVMMU
 598                         /*
 599                          * We don't support PV MMU when Linux and Xen is using
 600                          * different page granularity.
 601                          */
 602                         BUILD_BUG_ON(XEN_PAGE_SIZE != PAGE_SIZE);
 603
 604                         if (!xen_feature(XENFEAT_auto_translated_physmap)) {
 605                                 ret = xen_alloc_p2m_entry(page_to_pfn(page));
 606                                 if (ret < 0)
 607                                         goto out_undo;
 608                         }
 609 #endif
 610                 } else {
 611                         ret = add_ballooned_pages(nr_pages - pgno);
 612                         if (ret < 0)
 613                                 goto out_undo;
 614                 }
 615         }
 616         mutex_unlock(&balloon_mutex);
 617         return 0;
 618  out_undo:
 619         mutex_unlock(&balloon_mutex);
 620         free_xenballooned_pages(pgno, pages);
 621         return ret;
 622 }
 623 EXPORT_SYMBOL(alloc_xenballooned_pages);
 624
 625 /**
 626  * free_xenballooned_pages - return pages retrieved with get_ballooned_pages
 627  * @nr_pages: Number of pages
 628  * @pages: pages to return
 629  */
 630 void free_xenballooned_pages(int nr_pages, struct page **pages)
 631 {
 632         int i;
 633
 634         mutex_lock(&balloon_mutex);
 635
 636         for (i = 0; i < nr_pages; i++) {
 637                 if (pages[i])
 638                         balloon_append(pages[i]);
 639         }
 640
 641         balloon_stats.target_unpopulated -= nr_pages;
 642
 643         /* The balloon may be too large now. Shrink it if needed. */
 644         if (current_credit())
 645                 schedule_delayed_work(&balloon_worker, 0);
 646
 647         mutex_unlock(&balloon_mutex);
 648 }
 649 EXPORT_SYMBOL(free_xenballooned_pages);
 650
 651 #ifdef CONFIG_XEN_PV
 652 static void __init balloon_add_region(unsigned long start_pfn,
 653                                       unsigned long pages)
 654 {
 655         unsigned long pfn, extra_pfn_end;
 656         struct page *page;
 657
 658         /*
 659          * If the amount of usable memory has been limited (e.g., with
 660          * the 'mem' command line parameter), don't add pages beyond
 661          * this limit.
 662          */
 663         extra_pfn_end = min(max_pfn, start_pfn + pages);
 664
 665         for (pfn = start_pfn; pfn < extra_pfn_end; pfn++) {
 666                 page = pfn_to_page(pfn);
 667                 /* totalram_pages and totalhigh_pages do not
 668                    include the boot-time balloon extension, so
 669                    don't subtract from it. */
 670                 __balloon_append(page);
 671         }
 672
 673         balloon_stats.total_pages += extra_pfn_end - start_pfn;
 674 }
 675 #endif
 676
 677 static int __init balloon_init(void)
 678 {
 679         if (!xen_domain())
 680                 return -ENODEV;
 681
 682         pr_info("Initialising balloon driver\n");
 683
 684 #ifdef CONFIG_XEN_PV
 685         balloon_stats.current_pages = xen_pv_domain()
 686                 ? min(xen_start_info->nr_pages - xen_released_pages, max_pfn)
 687                 : get_num_physpages();
 688 #else
 689         balloon_stats.current_pages = get_num_physpages();
 690 #endif
 691         balloon_stats.target_pages  = balloon_stats.current_pages;
 692         balloon_stats.balloon_low   = 0;
 693         balloon_stats.balloon_high  = 0;
 694         balloon_stats.total_pages   = balloon_stats.current_pages;
 695
 696         balloon_stats.schedule_delay = 1;
 697         balloon_stats.max_schedule_delay = 32;
 698         balloon_stats.retry_count = 1;
 699         balloon_stats.max_retry_count = RETRY_UNLIMITED;
 700
 701 #ifdef CONFIG_XEN_BALLOON_MEMORY_HOTPLUG
 702         set_online_page_callback(&xen_online_page);
 703         register_memory_notifier(&xen_memory_nb);
 704         register_sysctl_table(xen_root);
 705 #endif
 706
 707 #ifdef CONFIG_XEN_PV
 708         {
 709                 int i;
 710
 711                 /*
 712                  * Initialize the balloon with pages from the extra memory
 713                  * regions (see arch/x86/xen/setup.c).
 714                  */
 715                 for (i = 0; i < XEN_EXTRA_MEM_MAX_REGIONS; i++)
 716                         if (xen_extra_mem[i].n_pfns)
 717                                 balloon_add_region(xen_extra_mem[i].start_pfn,
 718                                                    xen_extra_mem[i].n_pfns);
 719         }
 720 #endif
 721
 722         /* Init the xen-balloon driver. */
 723         xen_balloon_init();
 724
 725         return 0;
 726 }
 727 subsys_initcall(balloon_init);