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
  47 #include <asm/xen/hypervisor.h>
  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
  54 #include <xen/interface/memory.h>
  55 #include <xen/xenbus.h>
  56 #include <xen/features.h>
  57 #include <xen/page.h>
  58
  59 #define PAGES2KB(_p) ((_p)<<(PAGE_SHIFT-10))
  60
  61 #define BALLOON_CLASS_NAME "xen_memory"
  62
  63 struct balloon_stats {
  64         /* We aim for 'current allocation' == 'target allocation'. */
  65         unsigned long current_pages;
  66         unsigned long target_pages;
  67         /* We may hit the hard limit in Xen. If we do then we remember it. */
  68         unsigned long hard_limit;
  69         /*
  70          * Drivers may alter the memory reservation independently, but they
  71          * must inform the balloon driver so we avoid hitting the hard limit.
  72          */
  73         unsigned long driver_pages;
  74         /* Number of pages in high- and low-memory balloons. */
  75         unsigned long balloon_low;
  76         unsigned long balloon_high;
  77 };
  78
  79 static DEFINE_MUTEX(balloon_mutex);
  80
  81 static struct sys_device balloon_sysdev;
  82
  83 static int register_balloon(struct sys_device *sysdev);
  84
  85 /*
  86  * Protects atomic reservation decrease/increase against concurrent increases.
  87  * Also protects non-atomic updates of current_pages and driver_pages, and
  88  * balloon lists.
  89  */
  90 static DEFINE_SPINLOCK(balloon_lock);
  91
  92 static struct balloon_stats balloon_stats;
  93
  94 /* We increase/decrease in batches which fit in a page */
  95 static unsigned long frame_list[PAGE_SIZE / sizeof(unsigned long)];
  96
  97 /* VM /proc information for memory */
  98 extern unsigned long totalram_pages;
  99
 100 #ifdef CONFIG_HIGHMEM
 101 extern unsigned long totalhigh_pages;
 102 #define inc_totalhigh_pages() (totalhigh_pages++)
 103 #define dec_totalhigh_pages() (totalhigh_pages--)
 104 #else
 105 #define inc_totalhigh_pages() do {} while(0)
 106 #define dec_totalhigh_pages() do {} while(0)
 107 #endif
 108
 109 /* List of ballooned pages, threaded through the mem_map array. */
 110 static LIST_HEAD(ballooned_pages);
 111
 112 /* Main work function, always executed in process context. */
 113 static void balloon_process(struct work_struct *work);
 114 static DECLARE_WORK(balloon_worker, balloon_process);
 115 static struct timer_list balloon_timer;
 116
 117 /* When ballooning out (allocating memory to return to Xen) we don't really
 118    want the kernel to try too hard since that can trigger the oom killer. */
 119 #define GFP_BALLOON \
 120         (GFP_HIGHUSER | __GFP_NOWARN | __GFP_NORETRY | __GFP_NOMEMALLOC)
 121
 122 static void scrub_page(struct page *page)
 123 {
 124 #ifdef CONFIG_XEN_SCRUB_PAGES
 125         if (PageHighMem(page)) {
 126                 void *v = kmap(page);
 127                 clear_page(v);
 128                 kunmap(v);
 129         } else {
 130                 void *v = page_address(page);
 131                 clear_page(v);
 132         }
 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 /* balloon_retrieve: rescue a page from the balloon, if it is not empty. */
 151 static struct page *balloon_retrieve(void)
 152 {
 153         struct page *page;
 154
 155         if (list_empty(&ballooned_pages))
 156                 return NULL;
 157
 158         page = list_entry(ballooned_pages.next, struct page, lru);
 159         list_del(&page->lru);
 160
 161         if (PageHighMem(page)) {
 162                 balloon_stats.balloon_high--;
 163                 inc_totalhigh_pages();
 164         }
 165         else
 166                 balloon_stats.balloon_low--;
 167
 168         return page;
 169 }
 170
 171 static struct page *balloon_first_page(void)
 172 {
 173         if (list_empty(&ballooned_pages))
 174                 return NULL;
 175         return list_entry(ballooned_pages.next, struct page, lru);
 176 }
 177
 178 static struct page *balloon_next_page(struct page *page)
 179 {
 180         struct list_head *next = page->lru.next;
 181         if (next == &ballooned_pages)
 182                 return NULL;
 183         return list_entry(next, struct page, lru);
 184 }
 185
 186 static void balloon_alarm(unsigned long unused)
 187 {
 188         schedule_work(&balloon_worker);
 189 }
 190
 191 static unsigned long current_target(void)
 192 {
 193         unsigned long target = min(balloon_stats.target_pages, balloon_stats.hard_limit);
 194
 195         target = min(target,
 196                      balloon_stats.current_pages +
 197                      balloon_stats.balloon_low +
 198                      balloon_stats.balloon_high);
 199
 200         return target;
 201 }
 202
 203 static int increase_reservation(unsigned long nr_pages)
 204 {
 205         unsigned long  pfn, i, flags;
 206         struct page   *page;
 207         long           rc;
 208         struct xen_memory_reservation reservation = {
 209                 .address_bits = 0,
 210                 .extent_order = 0,
 211                 .domid        = DOMID_SELF
 212         };
 213
 214         if (nr_pages > ARRAY_SIZE(frame_list))
 215                 nr_pages = ARRAY_SIZE(frame_list);
 216
 217         spin_lock_irqsave(&balloon_lock, flags);
 218
 219         page = balloon_first_page();
 220         for (i = 0; i < nr_pages; i++) {
 221                 BUG_ON(page == NULL);
 222                 frame_list[i] = page_to_pfn(page);;
 223                 page = balloon_next_page(page);
 224         }
 225
 226         set_xen_guest_handle(reservation.extent_start, frame_list);
 227         reservation.nr_extents = nr_pages;
 228         rc = HYPERVISOR_memory_op(XENMEM_populate_physmap, &reservation);
 229         if (rc < nr_pages) {
 230                 if (rc > 0) {
 231                         int ret;
 232
 233                         /* We hit the Xen hard limit: reprobe. */
 234                         reservation.nr_extents = rc;
 235                         ret = HYPERVISOR_memory_op(XENMEM_decrease_reservation,
 236                                                    &reservation);
 237                         BUG_ON(ret != rc);
 238                 }
 239                 if (rc >= 0)
 240                         balloon_stats.hard_limit = (balloon_stats.current_pages + rc -
 241                                                     balloon_stats.driver_pages);
 242                 goto out;
 243         }
 244
 245         for (i = 0; i < nr_pages; i++) {
 246                 page = balloon_retrieve();
 247                 BUG_ON(page == NULL);
 248
 249                 pfn = page_to_pfn(page);
 250                 BUG_ON(!xen_feature(XENFEAT_auto_translated_physmap) &&
 251                        phys_to_machine_mapping_valid(pfn));
 252
 253                 set_phys_to_machine(pfn, frame_list[i]);
 254
 255                 /* Link back into the page tables if not highmem. */
 256                 if (pfn < max_low_pfn) {
 257                         int ret;
 258                         ret = HYPERVISOR_update_va_mapping(
 259                                 (unsigned long)__va(pfn << PAGE_SHIFT),
 260                                 mfn_pte(frame_list[i], PAGE_KERNEL),
 261                                 0);
 262                         BUG_ON(ret);
 263                 }
 264
 265                 /* Relinquish the page back to the allocator. */
 266                 ClearPageReserved(page);
 267                 init_page_count(page);
 268                 __free_page(page);
 269         }
 270
 271         balloon_stats.current_pages += nr_pages;
 272         totalram_pages = balloon_stats.current_pages;
 273
 274  out:
 275         spin_unlock_irqrestore(&balloon_lock, flags);
 276
 277         return 0;
 278 }
 279
 280 static int decrease_reservation(unsigned long nr_pages)
 281 {
 282         unsigned long  pfn, i, flags;
 283         struct page   *page;
 284         int            need_sleep = 0;
 285         int ret;
 286         struct xen_memory_reservation reservation = {
 287                 .address_bits = 0,
 288                 .extent_order = 0,
 289                 .domid        = DOMID_SELF
 290         };
 291
 292         if (nr_pages > ARRAY_SIZE(frame_list))
 293                 nr_pages = ARRAY_SIZE(frame_list);
 294
 295         for (i = 0; i < nr_pages; i++) {
 296                 if ((page = alloc_page(GFP_BALLOON)) == NULL) {
 297                         nr_pages = i;
 298                         need_sleep = 1;
 299                         break;
 300                 }
 301
 302                 pfn = page_to_pfn(page);
 303                 frame_list[i] = pfn_to_mfn(pfn);
 304
 305                 scrub_page(page);
 306         }
 307
 308         /* Ensure that ballooned highmem pages don't have kmaps. */
 309         kmap_flush_unused();
 310         flush_tlb_all();
 311
 312         spin_lock_irqsave(&balloon_lock, flags);
 313
 314         /* No more mappings: invalidate P2M and add to balloon. */
 315         for (i = 0; i < nr_pages; i++) {
 316                 pfn = mfn_to_pfn(frame_list[i]);
 317                 set_phys_to_machine(pfn, INVALID_P2M_ENTRY);
 318                 balloon_append(pfn_to_page(pfn));
 319         }
 320
 321         set_xen_guest_handle(reservation.extent_start, frame_list);
 322         reservation.nr_extents   = nr_pages;
 323         ret = HYPERVISOR_memory_op(XENMEM_decrease_reservation, &reservation);
 324         BUG_ON(ret != nr_pages);
 325
 326         balloon_stats.current_pages -= nr_pages;
 327         totalram_pages = balloon_stats.current_pages;
 328
 329         spin_unlock_irqrestore(&balloon_lock, flags);
 330
 331         return need_sleep;
 332 }
 333
 334 /*
 335  * We avoid multiple worker processes conflicting via the balloon mutex.
 336  * We may of course race updates of the target counts (which are protected
 337  * by the balloon lock), or with changes to the Xen hard limit, but we will
 338  * recover from these in time.
 339  */
 340 static void balloon_process(struct work_struct *work)
 341 {
 342         int need_sleep = 0;
 343         long credit;
 344
 345         mutex_lock(&balloon_mutex);
 346
 347         do {
 348                 credit = current_target() - balloon_stats.current_pages;
 349                 if (credit > 0)
 350                         need_sleep = (increase_reservation(credit) != 0);
 351                 if (credit < 0)
 352                         need_sleep = (decrease_reservation(-credit) != 0);
 353
 354 #ifndef CONFIG_PREEMPT
 355                 if (need_resched())
 356                         schedule();
 357 #endif
 358         } while ((credit != 0) && !need_sleep);
 359
 360         /* Schedule more work if there is some still to be done. */
 361         if (current_target() != balloon_stats.current_pages)
 362                 mod_timer(&balloon_timer, jiffies + HZ);
 363
 364         mutex_unlock(&balloon_mutex);
 365 }
 366
 367 /* Resets the Xen limit, sets new target, and kicks off processing. */
 368 static void balloon_set_new_target(unsigned long target)
 369 {
 370         /* No need for lock. Not read-modify-write updates. */
 371         balloon_stats.hard_limit   = ~0UL;
 372         balloon_stats.target_pages = target;
 373         schedule_work(&balloon_worker);
 374 }
 375
 376 static struct xenbus_watch target_watch =
 377 {
 378         .node = "memory/target"
 379 };
 380
 381 /* React to a change in the target key */
 382 static void watch_target(struct xenbus_watch *watch,
 383                          const char **vec, unsigned int len)
 384 {
 385         unsigned long long new_target;
 386         int err;
 387
 388         err = xenbus_scanf(XBT_NIL, "memory", "target", "%llu", &new_target);
 389         if (err != 1) {
 390                 /* This is ok (for domain0 at least) - so just return */
 391                 return;
 392         }
 393
 394         /* The given memory/target value is in KiB, so it needs converting to
 395          * pages. PAGE_SHIFT converts bytes to pages, hence PAGE_SHIFT - 10.
 396          */
 397         balloon_set_new_target(new_target >> (PAGE_SHIFT - 10));
 398 }
 399
 400 static int balloon_init_watcher(struct notifier_block *notifier,
 401                                 unsigned long event,
 402                                 void *data)
 403 {
 404         int err;
 405
 406         err = register_xenbus_watch(&target_watch);
 407         if (err)
 408                 printk(KERN_ERR "Failed to set balloon watcher\n");
 409
 410         return NOTIFY_DONE;
 411 }
 412
 413 static struct notifier_block xenstore_notifier;
 414
 415 static int __init balloon_init(void)
 416 {
 417         unsigned long pfn;
 418         struct page *page;
 419
 420         if (!xen_pv_domain())
 421                 return -ENODEV;
 422
 423         pr_info("xen_balloon: Initialising balloon driver.\n");
 424
 425         balloon_stats.current_pages = min(xen_start_info->nr_pages, max_pfn);
 426         totalram_pages   = balloon_stats.current_pages;
 427         balloon_stats.target_pages  = balloon_stats.current_pages;
 428         balloon_stats.balloon_low   = 0;
 429         balloon_stats.balloon_high  = 0;
 430         balloon_stats.driver_pages  = 0UL;
 431         balloon_stats.hard_limit    = ~0UL;
 432
 433         init_timer(&balloon_timer);
 434         balloon_timer.data = 0;
 435         balloon_timer.function = balloon_alarm;
 436
 437         register_balloon(&balloon_sysdev);
 438
 439         /* Initialise the balloon with excess memory space. */
 440         for (pfn = xen_start_info->nr_pages; pfn < max_pfn; pfn++) {
 441                 page = pfn_to_page(pfn);
 442                 if (!PageReserved(page))
 443                         balloon_append(page);
 444         }
 445
 446         target_watch.callback = watch_target;
 447         xenstore_notifier.notifier_call = balloon_init_watcher;
 448
 449         register_xenstore_notifier(&xenstore_notifier);
 450
 451         return 0;
 452 }
 453
 454 subsys_initcall(balloon_init);
 455
 456 static void balloon_exit(void)
 457 {
 458     /* XXX - release balloon here */
 459     return;
 460 }
 461
 462 module_exit(balloon_exit);
 463
 464 #define BALLOON_SHOW(name, format, args...)                             \
 465         static ssize_t show_##name(struct sys_device *dev,              \
 466                                    struct sysdev_attribute *attr,       \
 467                                    char *buf)                           \
 468         {                                                               \
 469                 return sprintf(buf, format, ##args);                    \
 470         }                                                               \
 471         static SYSDEV_ATTR(name, S_IRUGO, show_##name, NULL)
 472
 473 BALLOON_SHOW(current_kb, "%lu\n", PAGES2KB(balloon_stats.current_pages));
 474 BALLOON_SHOW(low_kb, "%lu\n", PAGES2KB(balloon_stats.balloon_low));
 475 BALLOON_SHOW(high_kb, "%lu\n", PAGES2KB(balloon_stats.balloon_high));
 476 BALLOON_SHOW(hard_limit_kb,
 477              (balloon_stats.hard_limit!=~0UL) ? "%lu\n" : "???\n",
 478              (balloon_stats.hard_limit!=~0UL) ? PAGES2KB(balloon_stats.hard_limit) : 0);
 479 BALLOON_SHOW(driver_kb, "%lu\n", PAGES2KB(balloon_stats.driver_pages));
 480
 481 static ssize_t show_target_kb(struct sys_device *dev, struct sysdev_attribute *attr,
 482                               char *buf)
 483 {
 484         return sprintf(buf, "%lu\n", PAGES2KB(balloon_stats.target_pages));
 485 }
 486
 487 static ssize_t store_target_kb(struct sys_device *dev,
 488                                struct sysdev_attribute *attr,
 489                                const char *buf,
 490                                size_t count)
 491 {
 492         char *endchar;
 493         unsigned long long target_bytes;
 494
 495         if (!capable(CAP_SYS_ADMIN))
 496                 return -EPERM;
 497
 498         target_bytes = memparse(buf, &endchar);
 499
 500         balloon_set_new_target(target_bytes >> PAGE_SHIFT);
 501
 502         return count;
 503 }
 504
 505 static SYSDEV_ATTR(target_kb, S_IRUGO | S_IWUSR,
 506                    show_target_kb, store_target_kb);
 507
 508 static struct sysdev_attribute *balloon_attrs[] = {
 509         &attr_target_kb,
 510 };
 511
 512 static struct attribute *balloon_info_attrs[] = {
 513         &attr_current_kb.attr,
 514         &attr_low_kb.attr,
 515         &attr_high_kb.attr,
 516         &attr_hard_limit_kb.attr,
 517         &attr_driver_kb.attr,
 518         NULL
 519 };
 520
 521 static struct attribute_group balloon_info_group = {
 522         .name = "info",
 523         .attrs = balloon_info_attrs,
 524 };
 525
 526 static struct sysdev_class balloon_sysdev_class = {
 527         .name = BALLOON_CLASS_NAME,
 528 };
 529
 530 static int register_balloon(struct sys_device *sysdev)
 531 {
 532         int i, error;
 533
 534         error = sysdev_class_register(&balloon_sysdev_class);
 535         if (error)
 536                 return error;
 537
 538         sysdev->id = 0;
 539         sysdev->cls = &balloon_sysdev_class;
 540
 541         error = sysdev_register(sysdev);
 542         if (error) {
 543                 sysdev_class_unregister(&balloon_sysdev_class);
 544                 return error;
 545         }
 546
 547         for (i = 0; i < ARRAY_SIZE(balloon_attrs); i++) {
 548                 error = sysdev_create_file(sysdev, balloon_attrs[i]);
 549                 if (error)
 550                         goto fail;
 551         }
 552
 553         error = sysfs_create_group(&sysdev->kobj, &balloon_info_group);
 554         if (error)
 555                 goto fail;
 556
 557         return 0;
 558
 559  fail:
 560         while (--i >= 0)
 561                 sysdev_remove_file(sysdev, balloon_attrs[i]);
 562         sysdev_unregister(sysdev);
 563         sysdev_class_unregister(&balloon_sysdev_class);
 564         return error;
 565 }
 566
 567 MODULE_LICENSE("GPL");