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