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 /* 255 * Host memory not allocated to dom0. We can use this range for hotplug-based 256 * ballooning. 257 * 258 * It's a type-less resource. Setting IORESOURCE_MEM will make resource 259 * management algorithms (arch_remove_reservations()) look into guest e820, 260 * which we don't want. 261 */ 262 static struct resource hostmem_resource = { 263 .name = "Host RAM", 264 }; 265 266 void __attribute__((weak)) __init arch_xen_balloon_init(struct resource *res) 267 {} 268 269 static struct resource *additional_memory_resource(phys_addr_t size) 270 { 271 struct resource *res, *res_hostmem; 272 int ret = -ENOMEM; 273 274 res = kzalloc(sizeof(*res), GFP_KERNEL); 275 if (!res) 276 return NULL; 277 278 res->name = "System RAM"; 279 res->flags = IORESOURCE_SYSTEM_RAM | IORESOURCE_BUSY; 280 281 res_hostmem = kzalloc(sizeof(*res), GFP_KERNEL); 282 if (res_hostmem) { 283 /* Try to grab a range from hostmem */ 284 res_hostmem->name = "Host memory"; 285 ret = allocate_resource(&hostmem_resource, res_hostmem, 286 size, 0, -1, 287 PAGES_PER_SECTION * PAGE_SIZE, NULL, NULL); 288 } 289 290 if (!ret) { 291 /* 292 * Insert this resource into iomem. Because hostmem_resource 293 * tracks portion of guest e820 marked as UNUSABLE noone else 294 * should try to use it. 295 */ 296 res->start = res_hostmem->start; 297 res->end = res_hostmem->end; 298 ret = insert_resource(&iomem_resource, res); 299 if (ret < 0) { 300 pr_err("Can't insert iomem_resource [%llx - %llx]\n", 301 res->start, res->end); 302 release_memory_resource(res_hostmem); 303 res_hostmem = NULL; 304 res->start = res->end = 0; 305 } 306 } 307 308 if (ret) { 309 ret = allocate_resource(&iomem_resource, res, 310 size, 0, -1, 311 PAGES_PER_SECTION * PAGE_SIZE, NULL, NULL); 312 if (ret < 0) { 313 pr_err("Cannot allocate new System RAM resource\n"); 314 kfree(res); 315 return NULL; 316 } 317 } 318 319 #ifdef CONFIG_SPARSEMEM 320 { 321 unsigned long limit = 1UL << (MAX_PHYSMEM_BITS - PAGE_SHIFT); 322 unsigned long pfn = res->start >> PAGE_SHIFT; 323 324 if (pfn > limit) { 325 pr_err("New System RAM resource outside addressable RAM (%lu > %lu)\n", 326 pfn, limit); 327 release_memory_resource(res); 328 release_memory_resource(res_hostmem); 329 return NULL; 330 } 331 } 332 #endif 333 334 return res; 335 } 336 337 static enum bp_state reserve_additional_memory(void) 338 { 339 long credit; 340 struct resource *resource; 341 int nid, rc; 342 unsigned long balloon_hotplug; 343 344 credit = balloon_stats.target_pages + balloon_stats.target_unpopulated 345 - balloon_stats.total_pages; 346 347 /* 348 * Already hotplugged enough pages? Wait for them to be 349 * onlined. 350 */ 351 if (credit <= 0) 352 return BP_WAIT; 353 354 balloon_hotplug = round_up(credit, PAGES_PER_SECTION); 355 356 resource = additional_memory_resource(balloon_hotplug * PAGE_SIZE); 357 if (!resource) 358 goto err; 359 360 nid = memory_add_physaddr_to_nid(resource->start); 361 362 #ifdef CONFIG_XEN_HAVE_PVMMU 363 /* 364 * We don't support PV MMU when Linux and Xen is using 365 * different page granularity. 366 */ 367 BUILD_BUG_ON(XEN_PAGE_SIZE != PAGE_SIZE); 368 369 /* 370 * add_memory() will build page tables for the new memory so 371 * the p2m must contain invalid entries so the correct 372 * non-present PTEs will be written. 373 * 374 * If a failure occurs, the original (identity) p2m entries 375 * are not restored since this region is now known not to 376 * conflict with any devices. 377 */ 378 if (!xen_feature(XENFEAT_auto_translated_physmap)) { 379 unsigned long pfn, i; 380 381 pfn = PFN_DOWN(resource->start); 382 for (i = 0; i < balloon_hotplug; i++) { 383 if (!set_phys_to_machine(pfn + i, INVALID_P2M_ENTRY)) { 384 pr_warn("set_phys_to_machine() failed, no memory added\n"); 385 goto err; 386 } 387 } 388 } 389 #endif 390 391 /* 392 * add_memory_resource() will call online_pages() which in its turn 393 * will call xen_online_page() callback causing deadlock if we don't 394 * release balloon_mutex here. Unlocking here is safe because the 395 * callers drop the mutex before trying again. 396 */ 397 mutex_unlock(&balloon_mutex); 398 rc = add_memory_resource(nid, resource, memhp_auto_online); 399 mutex_lock(&balloon_mutex); 400 401 if (rc) { 402 pr_warn("Cannot add additional memory (%i)\n", rc); 403 goto err; 404 } 405 406 balloon_stats.total_pages += balloon_hotplug; 407 408 return BP_WAIT; 409 err: 410 release_memory_resource(resource); 411 return BP_ECANCELED; 412 } 413 414 static void xen_online_page(struct page *page) 415 { 416 __online_page_set_limits(page); 417 418 mutex_lock(&balloon_mutex); 419 420 __balloon_append(page); 421 422 mutex_unlock(&balloon_mutex); 423 } 424 425 static int xen_memory_notifier(struct notifier_block *nb, unsigned long val, void *v) 426 { 427 if (val == MEM_ONLINE) 428 schedule_delayed_work(&balloon_worker, 0); 429 430 return NOTIFY_OK; 431 } 432 433 static struct notifier_block xen_memory_nb = { 434 .notifier_call = xen_memory_notifier, 435 .priority = 0 436 }; 437 #else 438 static enum bp_state reserve_additional_memory(void) 439 { 440 balloon_stats.target_pages = balloon_stats.current_pages; 441 return BP_ECANCELED; 442 } 443 #endif /* CONFIG_XEN_BALLOON_MEMORY_HOTPLUG */ 444 445 static long current_credit(void) 446 { 447 return balloon_stats.target_pages - balloon_stats.current_pages; 448 } 449 450 static bool balloon_is_inflated(void) 451 { 452 return balloon_stats.balloon_low || balloon_stats.balloon_high; 453 } 454 455 static enum bp_state increase_reservation(unsigned long nr_pages) 456 { 457 int rc; 458 unsigned long i; 459 struct page *page; 460 461 if (nr_pages > ARRAY_SIZE(frame_list)) 462 nr_pages = ARRAY_SIZE(frame_list); 463 464 page = list_first_entry_or_null(&ballooned_pages, struct page, lru); 465 for (i = 0; i < nr_pages; i++) { 466 if (!page) { 467 nr_pages = i; 468 break; 469 } 470 471 frame_list[i] = page_to_xen_pfn(page); 472 page = balloon_next_page(page); 473 } 474 475 rc = xenmem_reservation_increase(nr_pages, frame_list); 476 if (rc <= 0) 477 return BP_EAGAIN; 478 479 for (i = 0; i < rc; i++) { 480 page = balloon_retrieve(false); 481 BUG_ON(page == NULL); 482 483 xenmem_reservation_va_mapping_update(1, &page, &frame_list[i]); 484 485 /* Relinquish the page back to the allocator. */ 486 free_reserved_page(page); 487 } 488 489 balloon_stats.current_pages += rc; 490 491 return BP_DONE; 492 } 493 494 static enum bp_state decrease_reservation(unsigned long nr_pages, gfp_t gfp) 495 { 496 enum bp_state state = BP_DONE; 497 unsigned long i; 498 struct page *page, *tmp; 499 int ret; 500 LIST_HEAD(pages); 501 502 if (nr_pages > ARRAY_SIZE(frame_list)) 503 nr_pages = ARRAY_SIZE(frame_list); 504 505 for (i = 0; i < nr_pages; i++) { 506 page = alloc_page(gfp); 507 if (page == NULL) { 508 nr_pages = i; 509 state = BP_EAGAIN; 510 break; 511 } 512 adjust_managed_page_count(page, -1); 513 xenmem_reservation_scrub_page(page); 514 list_add(&page->lru, &pages); 515 } 516 517 /* 518 * Ensure that ballooned highmem pages don't have kmaps. 519 * 520 * Do this before changing the p2m as kmap_flush_unused() 521 * reads PTEs to obtain pages (and hence needs the original 522 * p2m entry). 523 */ 524 kmap_flush_unused(); 525 526 /* 527 * Setup the frame, update direct mapping, invalidate P2M, 528 * and add to balloon. 529 */ 530 i = 0; 531 list_for_each_entry_safe(page, tmp, &pages, lru) { 532 frame_list[i++] = xen_page_to_gfn(page); 533 534 xenmem_reservation_va_mapping_reset(1, &page); 535 536 list_del(&page->lru); 537 538 balloon_append(page); 539 } 540 541 flush_tlb_all(); 542 543 ret = xenmem_reservation_decrease(nr_pages, frame_list); 544 BUG_ON(ret != nr_pages); 545 546 balloon_stats.current_pages -= nr_pages; 547 548 return state; 549 } 550 551 /* 552 * As this is a work item it is guaranteed to run as a single instance only. 553 * We may of course race updates of the target counts (which are protected 554 * by the balloon lock), or with changes to the Xen hard limit, but we will 555 * recover from these in time. 556 */ 557 static void balloon_process(struct work_struct *work) 558 { 559 enum bp_state state = BP_DONE; 560 long credit; 561 562 563 do { 564 mutex_lock(&balloon_mutex); 565 566 credit = current_credit(); 567 568 if (credit > 0) { 569 if (balloon_is_inflated()) 570 state = increase_reservation(credit); 571 else 572 state = reserve_additional_memory(); 573 } 574 575 if (credit < 0) 576 state = decrease_reservation(-credit, GFP_BALLOON); 577 578 state = update_schedule(state); 579 580 mutex_unlock(&balloon_mutex); 581 582 cond_resched(); 583 584 } while (credit && state == BP_DONE); 585 586 /* Schedule more work if there is some still to be done. */ 587 if (state == BP_EAGAIN) 588 schedule_delayed_work(&balloon_worker, balloon_stats.schedule_delay * HZ); 589 } 590 591 /* Resets the Xen limit, sets new target, and kicks off processing. */ 592 void balloon_set_new_target(unsigned long target) 593 { 594 /* No need for lock. Not read-modify-write updates. */ 595 balloon_stats.target_pages = target; 596 schedule_delayed_work(&balloon_worker, 0); 597 } 598 EXPORT_SYMBOL_GPL(balloon_set_new_target); 599 600 static int add_ballooned_pages(int nr_pages) 601 { 602 enum bp_state st; 603 604 if (xen_hotplug_unpopulated) { 605 st = reserve_additional_memory(); 606 if (st != BP_ECANCELED) { 607 mutex_unlock(&balloon_mutex); 608 wait_event(balloon_wq, 609 !list_empty(&ballooned_pages)); 610 mutex_lock(&balloon_mutex); 611 return 0; 612 } 613 } 614 615 st = decrease_reservation(nr_pages, GFP_USER); 616 if (st != BP_DONE) 617 return -ENOMEM; 618 619 return 0; 620 } 621 622 /** 623 * alloc_xenballooned_pages - get pages that have been ballooned out 624 * @nr_pages: Number of pages to get 625 * @pages: pages returned 626 * @return 0 on success, error otherwise 627 */ 628 int alloc_xenballooned_pages(int nr_pages, struct page **pages) 629 { 630 int pgno = 0; 631 struct page *page; 632 int ret; 633 634 mutex_lock(&balloon_mutex); 635 636 balloon_stats.target_unpopulated += nr_pages; 637 638 while (pgno < nr_pages) { 639 page = balloon_retrieve(true); 640 if (page) { 641 pages[pgno++] = page; 642 #ifdef CONFIG_XEN_HAVE_PVMMU 643 /* 644 * We don't support PV MMU when Linux and Xen is using 645 * different page granularity. 646 */ 647 BUILD_BUG_ON(XEN_PAGE_SIZE != PAGE_SIZE); 648 649 if (!xen_feature(XENFEAT_auto_translated_physmap)) { 650 ret = xen_alloc_p2m_entry(page_to_pfn(page)); 651 if (ret < 0) 652 goto out_undo; 653 } 654 #endif 655 } else { 656 ret = add_ballooned_pages(nr_pages - pgno); 657 if (ret < 0) 658 goto out_undo; 659 } 660 } 661 mutex_unlock(&balloon_mutex); 662 return 0; 663 out_undo: 664 mutex_unlock(&balloon_mutex); 665 free_xenballooned_pages(pgno, pages); 666 return ret; 667 } 668 EXPORT_SYMBOL(alloc_xenballooned_pages); 669 670 /** 671 * free_xenballooned_pages - return pages retrieved with get_ballooned_pages 672 * @nr_pages: Number of pages 673 * @pages: pages to return 674 */ 675 void free_xenballooned_pages(int nr_pages, struct page **pages) 676 { 677 int i; 678 679 mutex_lock(&balloon_mutex); 680 681 for (i = 0; i < nr_pages; i++) { 682 if (pages[i]) 683 balloon_append(pages[i]); 684 } 685 686 balloon_stats.target_unpopulated -= nr_pages; 687 688 /* The balloon may be too large now. Shrink it if needed. */ 689 if (current_credit()) 690 schedule_delayed_work(&balloon_worker, 0); 691 692 mutex_unlock(&balloon_mutex); 693 } 694 EXPORT_SYMBOL(free_xenballooned_pages); 695 696 #ifdef CONFIG_XEN_PV 697 static void __init balloon_add_region(unsigned long start_pfn, 698 unsigned long pages) 699 { 700 unsigned long pfn, extra_pfn_end; 701 struct page *page; 702 703 /* 704 * If the amount of usable memory has been limited (e.g., with 705 * the 'mem' command line parameter), don't add pages beyond 706 * this limit. 707 */ 708 extra_pfn_end = min(max_pfn, start_pfn + pages); 709 710 for (pfn = start_pfn; pfn < extra_pfn_end; pfn++) { 711 page = pfn_to_page(pfn); 712 /* totalram_pages and totalhigh_pages do not 713 include the boot-time balloon extension, so 714 don't subtract from it. */ 715 __balloon_append(page); 716 } 717 718 balloon_stats.total_pages += extra_pfn_end - start_pfn; 719 } 720 #endif 721 722 static int __init balloon_init(void) 723 { 724 if (!xen_domain()) 725 return -ENODEV; 726 727 pr_info("Initialising balloon driver\n"); 728 729 #ifdef CONFIG_XEN_PV 730 balloon_stats.current_pages = xen_pv_domain() 731 ? min(xen_start_info->nr_pages - xen_released_pages, max_pfn) 732 : get_num_physpages(); 733 #else 734 balloon_stats.current_pages = get_num_physpages(); 735 #endif 736 balloon_stats.target_pages = balloon_stats.current_pages; 737 balloon_stats.balloon_low = 0; 738 balloon_stats.balloon_high = 0; 739 balloon_stats.total_pages = balloon_stats.current_pages; 740 741 balloon_stats.schedule_delay = 1; 742 balloon_stats.max_schedule_delay = 32; 743 balloon_stats.retry_count = 1; 744 balloon_stats.max_retry_count = RETRY_UNLIMITED; 745 746 #ifdef CONFIG_XEN_BALLOON_MEMORY_HOTPLUG 747 set_online_page_callback(&xen_online_page); 748 register_memory_notifier(&xen_memory_nb); 749 register_sysctl_table(xen_root); 750 751 arch_xen_balloon_init(&hostmem_resource); 752 #endif 753 754 #ifdef CONFIG_XEN_PV 755 { 756 int i; 757 758 /* 759 * Initialize the balloon with pages from the extra memory 760 * regions (see arch/x86/xen/setup.c). 761 */ 762 for (i = 0; i < XEN_EXTRA_MEM_MAX_REGIONS; i++) 763 if (xen_extra_mem[i].n_pfns) 764 balloon_add_region(xen_extra_mem[i].start_pfn, 765 xen_extra_mem[i].n_pfns); 766 } 767 #endif 768 769 /* Init the xen-balloon driver. */ 770 xen_balloon_init(); 771 772 return 0; 773 } 774 subsys_initcall(balloon_init); 775