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/highmem.h>
  45 #include <linux/list.h>
  46 #include <linux/sysdev.h>
  47
  48 #include <asm/xen/hypervisor.h>
  49 #include <asm/page.h>
  50 #include <asm/pgalloc.h>
  51 #include <asm/pgtable.h>
  52 #include <asm/uaccess.h>
  53 #include <asm/tlb.h>
  54
  55 #include <xen/interface/memory.h>
  56 #include <xen/balloon.h>
  57 #include <xen/xenbus.h>
  58 #include <xen/features.h>
  59 #include <xen/page.h>
  60
  61 #define PAGES2KB(_p) ((_p)<<(PAGE_SHIFT-10))
  62
  63 #define BALLOON_CLASS_NAME "xen_memory"
  64
  65 struct balloon_stats {
  66         /* We aim for 'current allocation' == 'target allocation'. */
  67         unsigned long current_pages;
  68         unsigned long target_pages;
  69         /* We may hit the hard limit in Xen. If we do then we remember it. */
  70         unsigned long hard_limit;
  71         /*
  72          * Drivers may alter the memory reservation independently, but they
  73          * must inform the balloon driver so we avoid hitting the hard limit.
  74          */
  75         unsigned long driver_pages;
  76         /* Number of pages in high- and low-memory balloons. */
  77         unsigned long balloon_low;
  78         unsigned long balloon_high;
  79 };
  80
  81 static DEFINE_MUTEX(balloon_mutex);
  82
  83 static struct sys_device balloon_sysdev;
  84
  85 static int register_balloon(struct sys_device *sysdev);
  86
  87 /*
  88  * Protects atomic reservation decrease/increase against concurrent increases.
  89  * Also protects non-atomic updates of current_pages and driver_pages, and
  90  * balloon lists.
  91  */
  92 static DEFINE_SPINLOCK(balloon_lock);
  93
  94 static struct balloon_stats balloon_stats;
  95
  96 /* We increase/decrease in batches which fit in a page */
  97 static unsigned long frame_list[PAGE_SIZE / sizeof(unsigned long)];
  98
  99 /* VM /proc information for memory */
 100 extern unsigned long totalram_pages;
 101
 102 #ifdef CONFIG_HIGHMEM
 103 extern unsigned long totalhigh_pages;
 104 #define inc_totalhigh_pages() (totalhigh_pages++)
 105 #define dec_totalhigh_pages() (totalhigh_pages--)
 106 #else
 107 #define inc_totalhigh_pages() do {} while(0)
 108 #define dec_totalhigh_pages() do {} while(0)
 109 #endif
 110
 111 /* List of ballooned pages, threaded through the mem_map array. */
 112 static LIST_HEAD(ballooned_pages);
 113
 114 /* Main work function, always executed in process context. */
 115 static void balloon_process(struct work_struct *work);
 116 static DECLARE_WORK(balloon_worker, balloon_process);
 117 static struct timer_list balloon_timer;
 118
 119 /* When ballooning out (allocating memory to return to Xen) we don't really
 120    want the kernel to try too hard since that can trigger the oom killer. */
 121 #define GFP_BALLOON \
 122         (GFP_HIGHUSER | __GFP_NOWARN | __GFP_NORETRY | __GFP_NOMEMALLOC)
 123
 124 static void scrub_page(struct page *page)
 125 {
 126 #ifdef CONFIG_XEN_SCRUB_PAGES
 127         if (PageHighMem(page)) {
 128                 void *v = kmap(page);
 129                 clear_page(v);
 130                 kunmap(v);
 131         } else {
 132                 void *v = page_address(page);
 133                 clear_page(v);
 134         }
 135 #endif
 136 }
 137
 138 /* balloon_append: add the given page to the balloon. */
 139 static void balloon_append(struct page *page)
 140 {
 141         /* Lowmem is re-populated first, so highmem pages go at list tail. */
 142         if (PageHighMem(page)) {
 143                 list_add_tail(&page->lru, &ballooned_pages);
 144                 balloon_stats.balloon_high++;
 145                 dec_totalhigh_pages();
 146         } else {
 147                 list_add(&page->lru, &ballooned_pages);
 148                 balloon_stats.balloon_low++;
 149         }
 150 }
 151
 152 /* balloon_retrieve: rescue a page from the balloon, if it is not empty. */
 153 static struct page *balloon_retrieve(void)
 154 {
 155         struct page *page;
 156
 157         if (list_empty(&ballooned_pages))
 158                 return NULL;
 159
 160         page = list_entry(ballooned_pages.next, struct page, lru);
 161         list_del(&page->lru);
 162
 163         if (PageHighMem(page)) {
 164                 balloon_stats.balloon_high--;
 165                 inc_totalhigh_pages();
 166         }
 167         else
 168                 balloon_stats.balloon_low--;
 169
 170         return page;
 171 }
 172
 173 static struct page *balloon_first_page(void)
 174 {
 175         if (list_empty(&ballooned_pages))
 176                 return NULL;
 177         return list_entry(ballooned_pages.next, struct page, lru);
 178 }
 179
 180 static struct page *balloon_next_page(struct page *page)
 181 {
 182         struct list_head *next = page->lru.next;
 183         if (next == &ballooned_pages)
 184                 return NULL;
 185         return list_entry(next, struct page, lru);
 186 }
 187
 188 static void balloon_alarm(unsigned long unused)
 189 {
 190         schedule_work(&balloon_worker);
 191 }
 192
 193 static unsigned long current_target(void)
 194 {
 195         unsigned long target = min(balloon_stats.target_pages, balloon_stats.hard_limit);
 196
 197         target = min(target,
 198                      balloon_stats.current_pages +
 199                      balloon_stats.balloon_low +
 200                      balloon_stats.balloon_high);
 201
 202         return target;
 203 }
 204
 205 static int increase_reservation(unsigned long nr_pages)
 206 {
 207         unsigned long  pfn, i, flags;
 208         struct page   *page;
 209         long           rc;
 210         struct xen_memory_reservation reservation = {
 211                 .address_bits = 0,
 212                 .extent_order = 0,
 213                 .domid        = DOMID_SELF
 214         };
 215
 216         if (nr_pages > ARRAY_SIZE(frame_list))
 217                 nr_pages = ARRAY_SIZE(frame_list);
 218
 219         spin_lock_irqsave(&balloon_lock, flags);
 220
 221         page = balloon_first_page();
 222         for (i = 0; i < nr_pages; i++) {
 223                 BUG_ON(page == NULL);
 224                 frame_list[i] = page_to_pfn(page);;
 225                 page = balloon_next_page(page);
 226         }
 227
 228         set_xen_guest_handle(reservation.extent_start, frame_list);
 229         reservation.nr_extents = nr_pages;
 230         rc = HYPERVISOR_memory_op(XENMEM_populate_physmap, &reservation);
 231         if (rc < nr_pages) {
 232                 if (rc > 0) {
 233                         int ret;
 234
 235                         /* We hit the Xen hard limit: reprobe. */
 236                         reservation.nr_extents = rc;
 237                         ret = HYPERVISOR_memory_op(XENMEM_decrease_reservation,
 238                                                    &reservation);
 239                         BUG_ON(ret != rc);
 240                 }
 241                 if (rc >= 0)
 242                         balloon_stats.hard_limit = (balloon_stats.current_pages + rc -
 243                                                     balloon_stats.driver_pages);
 244                 goto out;
 245         }
 246
 247         for (i = 0; i < nr_pages; i++) {
 248                 page = balloon_retrieve();
 249                 BUG_ON(page == NULL);
 250
 251                 pfn = page_to_pfn(page);
 252                 BUG_ON(!xen_feature(XENFEAT_auto_translated_physmap) &&
 253                        phys_to_machine_mapping_valid(pfn));
 254
 255                 set_phys_to_machine(pfn, frame_list[i]);
 256
 257                 /* Link back into the page tables if not highmem. */
 258                 if (pfn < max_low_pfn) {
 259                         int ret;
 260                         ret = HYPERVISOR_update_va_mapping(
 261                                 (unsigned long)__va(pfn << PAGE_SHIFT),
 262                                 mfn_pte(frame_list[i], PAGE_KERNEL),
 263                                 0);
 264                         BUG_ON(ret);
 265                 }
 266
 267                 /* Relinquish the page back to the allocator. */
 268                 ClearPageReserved(page);
 269                 init_page_count(page);
 270                 __free_page(page);
 271         }
 272
 273         balloon_stats.current_pages += nr_pages;
 274         totalram_pages = balloon_stats.current_pages;
 275
 276  out:
 277         spin_unlock_irqrestore(&balloon_lock, flags);
 278
 279         return 0;
 280 }
 281
 282 static int decrease_reservation(unsigned long nr_pages)
 283 {
 284         unsigned long  pfn, i, flags;
 285         struct page   *page;
 286         int            need_sleep = 0;
 287         int ret;
 288         struct xen_memory_reservation reservation = {
 289                 .address_bits = 0,
 290                 .extent_order = 0,
 291                 .domid        = DOMID_SELF
 292         };
 293
 294         if (nr_pages > ARRAY_SIZE(frame_list))
 295                 nr_pages = ARRAY_SIZE(frame_list);
 296
 297         for (i = 0; i < nr_pages; i++) {
 298                 if ((page = alloc_page(GFP_BALLOON)) == NULL) {
 299                         nr_pages = i;
 300                         need_sleep = 1;
 301                         break;
 302                 }
 303
 304                 pfn = page_to_pfn(page);
 305                 frame_list[i] = pfn_to_mfn(pfn);
 306
 307                 scrub_page(page);
 308         }
 309
 310         /* Ensure that ballooned highmem pages don't have kmaps. */
 311         kmap_flush_unused();
 312         flush_tlb_all();
 313
 314         spin_lock_irqsave(&balloon_lock, flags);
 315
 316         /* No more mappings: invalidate P2M and add to balloon. */
 317         for (i = 0; i < nr_pages; i++) {
 318                 pfn = mfn_to_pfn(frame_list[i]);
 319                 set_phys_to_machine(pfn, INVALID_P2M_ENTRY);
 320                 balloon_append(pfn_to_page(pfn));
 321         }
 322
 323         set_xen_guest_handle(reservation.extent_start, frame_list);
 324         reservation.nr_extents   = nr_pages;
 325         ret = HYPERVISOR_memory_op(XENMEM_decrease_reservation, &reservation);
 326         BUG_ON(ret != nr_pages);
 327
 328         balloon_stats.current_pages -= nr_pages;
 329         totalram_pages = balloon_stats.current_pages;
 330
 331         spin_unlock_irqrestore(&balloon_lock, flags);
 332
 333         return need_sleep;
 334 }
 335
 336 /*
 337  * We avoid multiple worker processes conflicting via the balloon mutex.
 338  * We may of course race updates of the target counts (which are protected
 339  * by the balloon lock), or with changes to the Xen hard limit, but we will
 340  * recover from these in time.
 341  */
 342 static void balloon_process(struct work_struct *work)
 343 {
 344         int need_sleep = 0;
 345         long credit;
 346
 347         mutex_lock(&balloon_mutex);
 348
 349         do {
 350                 credit = current_target() - balloon_stats.current_pages;
 351                 if (credit > 0)
 352                         need_sleep = (increase_reservation(credit) != 0);
 353                 if (credit < 0)
 354                         need_sleep = (decrease_reservation(-credit) != 0);
 355
 356 #ifndef CONFIG_PREEMPT
 357                 if (need_resched())
 358                         schedule();
 359 #endif
 360         } while ((credit != 0) && !need_sleep);
 361
 362         /* Schedule more work if there is some still to be done. */
 363         if (current_target() != balloon_stats.current_pages)
 364                 mod_timer(&balloon_timer, jiffies + HZ);
 365
 366         mutex_unlock(&balloon_mutex);
 367 }
 368
 369 /* Resets the Xen limit, sets new target, and kicks off processing. */
 370 static void balloon_set_new_target(unsigned long target)
 371 {
 372         /* No need for lock. Not read-modify-write updates. */
 373         balloon_stats.hard_limit   = ~0UL;
 374         balloon_stats.target_pages = target;
 375         schedule_work(&balloon_worker);
 376 }
 377
 378 static struct xenbus_watch target_watch =
 379 {
 380         .node = "memory/target"
 381 };
 382
 383 /* React to a change in the target key */
 384 static void watch_target(struct xenbus_watch *watch,
 385                          const char **vec, unsigned int len)
 386 {
 387         unsigned long long new_target;
 388         int err;
 389
 390         err = xenbus_scanf(XBT_NIL, "memory", "target", "%llu", &new_target);
 391         if (err != 1) {
 392                 /* This is ok (for domain0 at least) - so just return */
 393                 return;
 394         }
 395
 396         /* The given memory/target value is in KiB, so it needs converting to
 397          * pages. PAGE_SHIFT converts bytes to pages, hence PAGE_SHIFT - 10.
 398          */
 399         balloon_set_new_target(new_target >> (PAGE_SHIFT - 10));
 400 }
 401
 402 static int balloon_init_watcher(struct notifier_block *notifier,
 403                                 unsigned long event,
 404                                 void *data)
 405 {
 406         int err;
 407
 408         err = register_xenbus_watch(&target_watch);
 409         if (err)
 410                 printk(KERN_ERR "Failed to set balloon watcher\n");
 411
 412         return NOTIFY_DONE;
 413 }
 414
 415 static struct notifier_block xenstore_notifier;
 416
 417 static int __init balloon_init(void)
 418 {
 419         unsigned long pfn;
 420         struct page *page;
 421
 422         if (!xen_pv_domain())
 423                 return -ENODEV;
 424
 425         pr_info("xen_balloon: Initialising balloon driver.\n");
 426
 427         balloon_stats.current_pages = min(xen_start_info->nr_pages, max_pfn);
 428         totalram_pages   = balloon_stats.current_pages;
 429         balloon_stats.target_pages  = balloon_stats.current_pages;
 430         balloon_stats.balloon_low   = 0;
 431         balloon_stats.balloon_high  = 0;
 432         balloon_stats.driver_pages  = 0UL;
 433         balloon_stats.hard_limit    = ~0UL;
 434
 435         init_timer(&balloon_timer);
 436         balloon_timer.data = 0;
 437         balloon_timer.function = balloon_alarm;
 438
 439         register_balloon(&balloon_sysdev);
 440
 441         /* Initialise the balloon with excess memory space. */
 442         for (pfn = xen_start_info->nr_pages; pfn < max_pfn; pfn++) {
 443                 page = pfn_to_page(pfn);
 444                 if (!PageReserved(page))
 445                         balloon_append(page);
 446         }
 447
 448         target_watch.callback = watch_target;
 449         xenstore_notifier.notifier_call = balloon_init_watcher;
 450
 451         register_xenstore_notifier(&xenstore_notifier);
 452
 453         return 0;
 454 }
 455
 456 subsys_initcall(balloon_init);
 457
 458 static void balloon_exit(void)
 459 {
 460     /* XXX - release balloon here */
 461     return;
 462 }
 463
 464 module_exit(balloon_exit);
 465
 466 #define BALLOON_SHOW(name, format, args...)                             \
 467         static ssize_t show_##name(struct sys_device *dev,              \
 468                                    struct sysdev_attribute *attr,       \
 469                                    char *buf)                           \
 470         {                                                               \
 471                 return sprintf(buf, format, ##args);                    \
 472         }                                                               \
 473         static SYSDEV_ATTR(name, S_IRUGO, show_##name, NULL)
 474
 475 BALLOON_SHOW(current_kb, "%lu\n", PAGES2KB(balloon_stats.current_pages));
 476 BALLOON_SHOW(low_kb, "%lu\n", PAGES2KB(balloon_stats.balloon_low));
 477 BALLOON_SHOW(high_kb, "%lu\n", PAGES2KB(balloon_stats.balloon_high));
 478 BALLOON_SHOW(hard_limit_kb,
 479              (balloon_stats.hard_limit!=~0UL) ? "%lu\n" : "???\n",
 480              (balloon_stats.hard_limit!=~0UL) ? PAGES2KB(balloon_stats.hard_limit) : 0);
 481 BALLOON_SHOW(driver_kb, "%lu\n", PAGES2KB(balloon_stats.driver_pages));
 482
 483 static ssize_t show_target_kb(struct sys_device *dev, struct sysdev_attribute *attr,
 484                               char *buf)
 485 {
 486         return sprintf(buf, "%lu\n", PAGES2KB(balloon_stats.target_pages));
 487 }
 488
 489 static ssize_t store_target_kb(struct sys_device *dev,
 490                                struct sysdev_attribute *attr,
 491                                const char *buf,
 492                                size_t count)
 493 {
 494         char *endchar;
 495         unsigned long long target_bytes;
 496
 497         if (!capable(CAP_SYS_ADMIN))
 498                 return -EPERM;
 499
 500         target_bytes = memparse(buf, &endchar);
 501
 502         balloon_set_new_target(target_bytes >> PAGE_SHIFT);
 503
 504         return count;
 505 }
 506
 507 static SYSDEV_ATTR(target_kb, S_IRUGO | S_IWUSR,
 508                    show_target_kb, store_target_kb);
 509
 510 static struct sysdev_attribute *balloon_attrs[] = {
 511         &attr_target_kb,
 512 };
 513
 514 static struct attribute *balloon_info_attrs[] = {
 515         &attr_current_kb.attr,
 516         &attr_low_kb.attr,
 517         &attr_high_kb.attr,
 518         &attr_hard_limit_kb.attr,
 519         &attr_driver_kb.attr,
 520         NULL
 521 };
 522
 523 static struct attribute_group balloon_info_group = {
 524         .name = "info",
 525         .attrs = balloon_info_attrs,
 526 };
 527
 528 static struct sysdev_class balloon_sysdev_class = {
 529         .name = BALLOON_CLASS_NAME,
 530 };
 531
 532 static int register_balloon(struct sys_device *sysdev)
 533 {
 534         int i, error;
 535
 536         error = sysdev_class_register(&balloon_sysdev_class);
 537         if (error)
 538                 return error;
 539
 540         sysdev->id = 0;
 541         sysdev->cls = &balloon_sysdev_class;
 542
 543         error = sysdev_register(sysdev);
 544         if (error) {
 545                 sysdev_class_unregister(&balloon_sysdev_class);
 546                 return error;
 547         }
 548
 549         for (i = 0; i < ARRAY_SIZE(balloon_attrs); i++) {
 550                 error = sysdev_create_file(sysdev, balloon_attrs[i]);
 551                 if (error)
 552                         goto fail;
 553         }
 554
 555         error = sysfs_create_group(&sysdev->kobj, &balloon_info_group);
 556         if (error)
 557                 goto fail;
 558
 559         return 0;
 560
 561  fail:
 562         while (--i >= 0)
 563                 sysdev_remove_file(sysdev, balloon_attrs[i]);
 564         sysdev_unregister(sysdev);
 565         sysdev_class_unregister(&balloon_sysdev_class);
 566         return error;
 567 }
 568
 569 MODULE_LICENSE("GPL");