drivers/xen/balloon.c

   1 /******************************************************************************
   2  * balloon.c
   3  *
   4  * Xen balloon driver - enables returning/claiming memory to/from Xen.
   5  *
   6  * Copyright (c) 2003, B Dragovic
   7  * Copyright (c) 2003-2004, M Williamson, K Fraser
   8  * Copyright (c) 2005 Dan M. Smith, IBM Corporation
   9  *
  10  * This program is free software; you can redistribute it and/or
  11  * modify it under the terms of the GNU General Public License version 2
  12  * as published by the Free Software Foundation; or, when distributed
  13  * separately from the Linux kernel or incorporated into other
  14  * software packages, subject to the following license:
  15  *
  16  * Permission is hereby granted, free of charge, to any person obtaining a copy
  17  * of this source file (the "Software"), to deal in the Software without
  18  * restriction, including without limitation the rights to use, copy, modify,
  19  * merge, publish, distribute, sublicense, and/or sell copies of the Software,
  20  * and to permit persons to whom the Software is furnished to do so, subject to
  21  * the following conditions:
  22  *
  23  * The above copyright notice and this permission notice shall be included in
  24  * all copies or substantial portions of the Software.
  25  *
  26  * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
  27  * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
  28  * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
  29  * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
  30  * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
  31  * FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS
  32  * IN THE SOFTWARE.
  33  */
  34
  35 #include <linux/kernel.h>
  36 #include <linux/module.h>
  37 #include <linux/sched.h>
  38 #include <linux/errno.h>
  39 #include <linux/mm.h>
  40 #include <linux/bootmem.h>
  41 #include <linux/pagemap.h>
  42 #include <linux/highmem.h>
  43 #include <linux/mutex.h>
  44 #include <linux/list.h>
  45 #include <linux/sysdev.h>
  46 #include <linux/gfp.h>
  47
  48 #include <asm/page.h>
  49 #include <asm/pgalloc.h>
  50 #include <asm/pgtable.h>
  51 #include <asm/uaccess.h>
  52 #include <asm/tlb.h>
  53 #include <asm/e820.h>
  54
  55 #include <asm/xen/hypervisor.h>
  56 #include <asm/xen/hypercall.h>
  57
  58 #include <xen/xen.h>
  59 #include <xen/interface/xen.h>
  60 #include <xen/interface/memory.h>
  61 #include <xen/xenbus.h>
  62 #include <xen/features.h>
  63 #include <xen/page.h>
  64
  65 #define PAGES2KB(_p) ((_p)<<(PAGE_SHIFT-10))
  66
  67 #define BALLOON_CLASS_NAME "xen_memory"
  68
  69 /*
  70  * balloon_process() state:
  71  *
  72  * BP_DONE: done or nothing to do,
  73  * BP_EAGAIN: error, go to sleep,
  74  * BP_ECANCELED: error, balloon operation canceled.
  75  */
  76
  77 enum bp_state {
  78         BP_DONE,
  79         BP_EAGAIN,
  80         BP_ECANCELED
  81 };
  82
  83 #define RETRY_UNLIMITED 0
  84
  85 struct balloon_stats {
  86         /* We aim for 'current allocation' == 'target allocation'. */
  87         unsigned long current_pages;
  88         unsigned long target_pages;
  89         /* Number of pages in high- and low-memory balloons. */
  90         unsigned long balloon_low;
  91         unsigned long balloon_high;
  92         unsigned long schedule_delay;
  93         unsigned long max_schedule_delay;
  94         unsigned long retry_count;
  95         unsigned long max_retry_count;
  96 };
  97
  98 static DEFINE_MUTEX(balloon_mutex);
  99
 100 static struct sys_device balloon_sysdev;
 101
 102 static int register_balloon(struct sys_device *sysdev);
 103
 104 static struct balloon_stats balloon_stats;
 105
 106 /* We increase/decrease in batches which fit in a page */
 107 static unsigned long frame_list[PAGE_SIZE / sizeof(unsigned long)];
 108
 109 #ifdef CONFIG_HIGHMEM
 110 #define inc_totalhigh_pages() (totalhigh_pages++)
 111 #define dec_totalhigh_pages() (totalhigh_pages--)
 112 #else
 113 #define inc_totalhigh_pages() do {} while(0)
 114 #define dec_totalhigh_pages() do {} while(0)
 115 #endif
 116
 117 /* List of ballooned pages, threaded through the mem_map array. */
 118 static LIST_HEAD(ballooned_pages);
 119
 120 /* Main work function, always executed in process context. */
 121 static void balloon_process(struct work_struct *work);
 122 static DECLARE_DELAYED_WORK(balloon_worker, balloon_process);
 123
 124 /* When ballooning out (allocating memory to return to Xen) we don't really
 125    want the kernel to try too hard since that can trigger the oom killer. */
 126 #define GFP_BALLOON \
 127         (GFP_HIGHUSER | __GFP_NOWARN | __GFP_NORETRY | __GFP_NOMEMALLOC)
 128
 129 static void scrub_page(struct page *page)
 130 {
 131 #ifdef CONFIG_XEN_SCRUB_PAGES
 132         clear_highpage(page);
 133 #endif
 134 }
 135
 136 /* balloon_append: add the given page to the balloon. */
 137 static void __balloon_append(struct page *page)
 138 {
 139         /* Lowmem is re-populated first, so highmem pages go at list tail. */
 140         if (PageHighMem(page)) {
 141                 list_add_tail(&page->lru, &ballooned_pages);
 142                 balloon_stats.balloon_high++;
 143                 dec_totalhigh_pages();
 144         } else {
 145                 list_add(&page->lru, &ballooned_pages);
 146                 balloon_stats.balloon_low++;
 147         }
 148 }
 149
 150 static void balloon_append(struct page *page)
 151 {
 152         __balloon_append(page);
 153         totalram_pages--;
 154 }
 155
 156 /* balloon_retrieve: rescue a page from the balloon, if it is not empty. */
 157 static struct page *balloon_retrieve(void)
 158 {
 159         struct page *page;
 160
 161         if (list_empty(&ballooned_pages))
 162                 return NULL;
 163
 164         page = list_entry(ballooned_pages.next, struct page, lru);
 165         list_del(&page->lru);
 166
 167         if (PageHighMem(page)) {
 168                 balloon_stats.balloon_high--;
 169                 inc_totalhigh_pages();
 170         }
 171         else
 172                 balloon_stats.balloon_low--;
 173
 174         totalram_pages++;
 175
 176         return page;
 177 }
 178
 179 static struct page *balloon_first_page(void)
 180 {
 181         if (list_empty(&ballooned_pages))
 182                 return NULL;
 183         return list_entry(ballooned_pages.next, struct page, lru);
 184 }
 185
 186 static struct page *balloon_next_page(struct page *page)
 187 {
 188         struct list_head *next = page->lru.next;
 189         if (next == &ballooned_pages)
 190                 return NULL;
 191         return list_entry(next, struct page, lru);
 192 }
 193
 194 static enum bp_state update_schedule(enum bp_state state)
 195 {
 196         if (state == BP_DONE) {
 197                 balloon_stats.schedule_delay = 1;
 198                 balloon_stats.retry_count = 1;
 199                 return BP_DONE;
 200         }
 201
 202         ++balloon_stats.retry_count;
 203
 204         if (balloon_stats.max_retry_count != RETRY_UNLIMITED &&
 205                         balloon_stats.retry_count > balloon_stats.max_retry_count) {
 206                 balloon_stats.schedule_delay = 1;
 207                 balloon_stats.retry_count = 1;
 208                 return BP_ECANCELED;
 209         }
 210
 211         balloon_stats.schedule_delay <<= 1;
 212
 213         if (balloon_stats.schedule_delay > balloon_stats.max_schedule_delay)
 214                 balloon_stats.schedule_delay = balloon_stats.max_schedule_delay;
 215
 216         return BP_EAGAIN;
 217 }
 218
 219 static unsigned long current_target(void)
 220 {
 221         unsigned long target = balloon_stats.target_pages;
 222
 223         target = min(target,
 224                      balloon_stats.current_pages +
 225                      balloon_stats.balloon_low +
 226                      balloon_stats.balloon_high);
 227
 228         return target;
 229 }
 230
 231 static enum bp_state increase_reservation(unsigned long nr_pages)
 232 {
 233         int rc;
 234         unsigned long  pfn, i;
 235         struct page   *page;
 236         struct xen_memory_reservation reservation = {
 237                 .address_bits = 0,
 238                 .extent_order = 0,
 239                 .domid        = DOMID_SELF
 240         };
 241
 242         if (nr_pages > ARRAY_SIZE(frame_list))
 243                 nr_pages = ARRAY_SIZE(frame_list);
 244
 245         page = balloon_first_page();
 246         for (i = 0; i < nr_pages; i++) {
 247                 if (!page) {
 248                         nr_pages = i;
 249                         break;
 250                 }
 251                 frame_list[i] = page_to_pfn(page);
 252                 page = balloon_next_page(page);
 253         }
 254
 255         set_xen_guest_handle(reservation.extent_start, frame_list);
 256         reservation.nr_extents = nr_pages;
 257         rc = HYPERVISOR_memory_op(XENMEM_populate_physmap, &reservation);
 258         if (rc <= 0)
 259                 return BP_EAGAIN;
 260
 261         for (i = 0; i < rc; i++) {
 262                 page = balloon_retrieve();
 263                 BUG_ON(page == NULL);
 264
 265                 pfn = page_to_pfn(page);
 266                 BUG_ON(!xen_feature(XENFEAT_auto_translated_physmap) &&
 267                        phys_to_machine_mapping_valid(pfn));
 268
 269                 set_phys_to_machine(pfn, frame_list[i]);
 270
 271                 /* Link back into the page tables if not highmem. */
 272                 if (pfn < max_low_pfn) {
 273                         int ret;
 274                         ret = HYPERVISOR_update_va_mapping(
 275                                 (unsigned long)__va(pfn << PAGE_SHIFT),
 276                                 mfn_pte(frame_list[i], PAGE_KERNEL),
 277                                 0);
 278                         BUG_ON(ret);
 279                 }
 280
 281                 /* Relinquish the page back to the allocator. */
 282                 ClearPageReserved(page);
 283                 init_page_count(page);
 284                 __free_page(page);
 285         }
 286
 287         balloon_stats.current_pages += rc;
 288
 289         return BP_DONE;
 290 }
 291
 292 static enum bp_state decrease_reservation(unsigned long nr_pages)
 293 {
 294         enum bp_state state = BP_DONE;
 295         unsigned long  pfn, i;
 296         struct page   *page;
 297         int ret;
 298         struct xen_memory_reservation reservation = {
 299                 .address_bits = 0,
 300                 .extent_order = 0,
 301                 .domid        = DOMID_SELF
 302         };
 303
 304         if (nr_pages > ARRAY_SIZE(frame_list))
 305                 nr_pages = ARRAY_SIZE(frame_list);
 306
 307         for (i = 0; i < nr_pages; i++) {
 308                 if ((page = alloc_page(GFP_BALLOON)) == NULL) {
 309                         nr_pages = i;
 310                         state = BP_EAGAIN;
 311                         break;
 312                 }
 313
 314                 pfn = page_to_pfn(page);
 315                 frame_list[i] = pfn_to_mfn(pfn);
 316
 317                 scrub_page(page);
 318
 319                 if (!PageHighMem(page)) {
 320                         ret = HYPERVISOR_update_va_mapping(
 321                                 (unsigned long)__va(pfn << PAGE_SHIFT),
 322                                 __pte_ma(0), 0);
 323                         BUG_ON(ret);
 324                 }
 325
 326         }
 327
 328         /* Ensure that ballooned highmem pages don't have kmaps. */
 329         kmap_flush_unused();
 330         flush_tlb_all();
 331
 332         /* No more mappings: invalidate P2M and add to balloon. */
 333         for (i = 0; i < nr_pages; i++) {
 334                 pfn = mfn_to_pfn(frame_list[i]);
 335                 set_phys_to_machine(pfn, INVALID_P2M_ENTRY);
 336                 balloon_append(pfn_to_page(pfn));
 337         }
 338
 339         set_xen_guest_handle(reservation.extent_start, frame_list);
 340         reservation.nr_extents   = nr_pages;
 341         ret = HYPERVISOR_memory_op(XENMEM_decrease_reservation, &reservation);
 342         BUG_ON(ret != nr_pages);
 343
 344         balloon_stats.current_pages -= nr_pages;
 345
 346         return state;
 347 }
 348
 349 /*
 350  * We avoid multiple worker processes conflicting via the balloon mutex.
 351  * We may of course race updates of the target counts (which are protected
 352  * by the balloon lock), or with changes to the Xen hard limit, but we will
 353  * recover from these in time.
 354  */
 355 static void balloon_process(struct work_struct *work)
 356 {
 357         enum bp_state state = BP_DONE;
 358         long credit;
 359
 360         mutex_lock(&balloon_mutex);
 361
 362         do {
 363                 credit = current_target() - balloon_stats.current_pages;
 364
 365                 if (credit > 0)
 366                         state = increase_reservation(credit);
 367
 368                 if (credit < 0)
 369                         state = decrease_reservation(-credit);
 370
 371                 state = update_schedule(state);
 372
 373 #ifndef CONFIG_PREEMPT
 374                 if (need_resched())
 375                         schedule();
 376 #endif
 377         } while (credit && state == BP_DONE);
 378
 379         /* Schedule more work if there is some still to be done. */
 380         if (state == BP_EAGAIN)
 381                 schedule_delayed_work(&balloon_worker, balloon_stats.schedule_delay * HZ);
 382
 383         mutex_unlock(&balloon_mutex);
 384 }
 385
 386 /* Resets the Xen limit, sets new target, and kicks off processing. */
 387 static void balloon_set_new_target(unsigned long target)
 388 {
 389         /* No need for lock. Not read-modify-write updates. */
 390         balloon_stats.target_pages = target;
 391         schedule_delayed_work(&balloon_worker, 0);
 392 }
 393
 394 static struct xenbus_watch target_watch =
 395 {
 396         .node = "memory/target"
 397 };
 398
 399 /* React to a change in the target key */
 400 static void watch_target(struct xenbus_watch *watch,
 401                          const char **vec, unsigned int len)
 402 {
 403         unsigned long long new_target;
 404         int err;
 405
 406         err = xenbus_scanf(XBT_NIL, "memory", "target", "%llu", &new_target);
 407         if (err != 1) {
 408                 /* This is ok (for domain0 at least) - so just return */
 409                 return;
 410         }
 411
 412         /* The given memory/target value is in KiB, so it needs converting to
 413          * pages. PAGE_SHIFT converts bytes to pages, hence PAGE_SHIFT - 10.
 414          */
 415         balloon_set_new_target(new_target >> (PAGE_SHIFT - 10));
 416 }
 417
 418 static int balloon_init_watcher(struct notifier_block *notifier,
 419                                 unsigned long event,
 420                                 void *data)
 421 {
 422         int err;
 423
 424         err = register_xenbus_watch(&target_watch);
 425         if (err)
 426                 printk(KERN_ERR "Failed to set balloon watcher\n");
 427
 428         return NOTIFY_DONE;
 429 }
 430
 431 static struct notifier_block xenstore_notifier;
 432
 433 static int __init balloon_init(void)
 434 {
 435         unsigned long pfn, extra_pfn_end;
 436         struct page *page;
 437
 438         if (!xen_pv_domain())
 439                 return -ENODEV;
 440
 441         pr_info("xen_balloon: Initialising balloon driver.\n");
 442
 443         balloon_stats.current_pages = min(xen_start_info->nr_pages, max_pfn);
 444         balloon_stats.target_pages  = balloon_stats.current_pages;
 445         balloon_stats.balloon_low   = 0;
 446         balloon_stats.balloon_high  = 0;
 447
 448         balloon_stats.schedule_delay = 1;
 449         balloon_stats.max_schedule_delay = 32;
 450         balloon_stats.retry_count = 1;
 451         balloon_stats.max_retry_count = RETRY_UNLIMITED;
 452
 453         register_balloon(&balloon_sysdev);
 454
 455         /*
 456          * Initialise the balloon with excess memory space.  We need
 457          * to make sure we don't add memory which doesn't exist or
 458          * logically exist.  The E820 map can be trimmed to be smaller
 459          * than the amount of physical memory due to the mem= command
 460          * line parameter.  And if this is a 32-bit non-HIGHMEM kernel
 461          * on a system with memory which requires highmem to access,
 462          * don't try to use it.
 463          */
 464         extra_pfn_end = min(min(max_pfn, e820_end_of_ram_pfn()),
 465                             (unsigned long)PFN_DOWN(xen_extra_mem_start + xen_extra_mem_size));
 466         for (pfn = PFN_UP(xen_extra_mem_start);
 467              pfn < extra_pfn_end;
 468              pfn++) {
 469                 page = pfn_to_page(pfn);
 470                 /* totalram_pages doesn't include the boot-time
 471                    balloon extension, so don't subtract from it. */
 472                 __balloon_append(page);
 473         }
 474
 475         target_watch.callback = watch_target;
 476         xenstore_notifier.notifier_call = balloon_init_watcher;
 477
 478         register_xenstore_notifier(&xenstore_notifier);
 479
 480         return 0;
 481 }
 482
 483 subsys_initcall(balloon_init);
 484
 485 static void balloon_exit(void)
 486 {
 487     /* XXX - release balloon here */
 488     return;
 489 }
 490
 491 module_exit(balloon_exit);
 492
 493 #define BALLOON_SHOW(name, format, args...)                             \
 494         static ssize_t show_##name(struct sys_device *dev,              \
 495                                    struct sysdev_attribute *attr,       \
 496                                    char *buf)                           \
 497         {                                                               \
 498                 return sprintf(buf, format, ##args);                    \
 499         }                                                               \
 500         static SYSDEV_ATTR(name, S_IRUGO, show_##name, NULL)
 501
 502 BALLOON_SHOW(current_kb, "%lu\n", PAGES2KB(balloon_stats.current_pages));
 503 BALLOON_SHOW(low_kb, "%lu\n", PAGES2KB(balloon_stats.balloon_low));
 504 BALLOON_SHOW(high_kb, "%lu\n", PAGES2KB(balloon_stats.balloon_high));
 505
 506 static SYSDEV_ULONG_ATTR(schedule_delay, 0444, balloon_stats.schedule_delay);
 507 static SYSDEV_ULONG_ATTR(max_schedule_delay, 0644, balloon_stats.max_schedule_delay);
 508 static SYSDEV_ULONG_ATTR(retry_count, 0444, balloon_stats.retry_count);
 509 static SYSDEV_ULONG_ATTR(max_retry_count, 0644, balloon_stats.max_retry_count);
 510
 511 static ssize_t show_target_kb(struct sys_device *dev, struct sysdev_attribute *attr,
 512                               char *buf)
 513 {
 514         return sprintf(buf, "%lu\n", PAGES2KB(balloon_stats.target_pages));
 515 }
 516
 517 static ssize_t store_target_kb(struct sys_device *dev,
 518                                struct sysdev_attribute *attr,
 519                                const char *buf,
 520                                size_t count)
 521 {
 522         char *endchar;
 523         unsigned long long target_bytes;
 524
 525         if (!capable(CAP_SYS_ADMIN))
 526                 return -EPERM;
 527
 528         target_bytes = simple_strtoull(buf, &endchar, 0) * 1024;
 529
 530         balloon_set_new_target(target_bytes >> PAGE_SHIFT);
 531
 532         return count;
 533 }
 534
 535 static SYSDEV_ATTR(target_kb, S_IRUGO | S_IWUSR,
 536                    show_target_kb, store_target_kb);
 537
 538
 539 static ssize_t show_target(struct sys_device *dev, struct sysdev_attribute *attr,
 540                               char *buf)
 541 {
 542         return sprintf(buf, "%llu\n",
 543                        (unsigned long long)balloon_stats.target_pages
 544                        << PAGE_SHIFT);
 545 }
 546
 547 static ssize_t store_target(struct sys_device *dev,
 548                             struct sysdev_attribute *attr,
 549                             const char *buf,
 550                             size_t count)
 551 {
 552         char *endchar;
 553         unsigned long long target_bytes;
 554
 555         if (!capable(CAP_SYS_ADMIN))
 556                 return -EPERM;
 557
 558         target_bytes = memparse(buf, &endchar);
 559
 560         balloon_set_new_target(target_bytes >> PAGE_SHIFT);
 561
 562         return count;
 563 }
 564
 565 static SYSDEV_ATTR(target, S_IRUGO | S_IWUSR,
 566                    show_target, store_target);
 567
 568
 569 static struct sysdev_attribute *balloon_attrs[] = {
 570         &attr_target_kb,
 571         &attr_target,
 572         &attr_schedule_delay.attr,
 573         &attr_max_schedule_delay.attr,
 574         &attr_retry_count.attr,
 575         &attr_max_retry_count.attr
 576 };
 577
 578 static struct attribute *balloon_info_attrs[] = {
 579         &attr_current_kb.attr,
 580         &attr_low_kb.attr,
 581         &attr_high_kb.attr,
 582         NULL
 583 };
 584
 585 static struct attribute_group balloon_info_group = {
 586         .name = "info",
 587         .attrs = balloon_info_attrs,
 588 };
 589
 590 static struct sysdev_class balloon_sysdev_class = {
 591         .name = BALLOON_CLASS_NAME,
 592 };
 593
 594 static int register_balloon(struct sys_device *sysdev)
 595 {
 596         int i, error;
 597
 598         error = sysdev_class_register(&balloon_sysdev_class);
 599         if (error)
 600                 return error;
 601
 602         sysdev->id = 0;
 603         sysdev->cls = &balloon_sysdev_class;
 604
 605         error = sysdev_register(sysdev);
 606         if (error) {
 607                 sysdev_class_unregister(&balloon_sysdev_class);
 608                 return error;
 609         }
 610
 611         for (i = 0; i < ARRAY_SIZE(balloon_attrs); i++) {
 612                 error = sysdev_create_file(sysdev, balloon_attrs[i]);
 613                 if (error)
 614                         goto fail;
 615         }
 616
 617         error = sysfs_create_group(&sysdev->kobj, &balloon_info_group);
 618         if (error)
 619                 goto fail;
 620
 621         return 0;
 622
 623  fail:
 624         while (--i >= 0)
 625                 sysdev_remove_file(sysdev, balloon_attrs[i]);
 626         sysdev_unregister(sysdev);
 627         sysdev_class_unregister(&balloon_sysdev_class);
 628         return error;
 629 }
 630
 631 MODULE_LICENSE("GPL");