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
  54 #include <asm/xen/hypervisor.h>
  55 #include <asm/xen/hypercall.h>
  56
  57 #include <xen/xen.h>
  58 #include <xen/interface/xen.h>
  59 #include <xen/interface/memory.h>
  60 #include <xen/xenbus.h>
  61 #include <xen/features.h>
  62 #include <xen/page.h>
  63
  64 #define PAGES2KB(_p) ((_p)<<(PAGE_SHIFT-10))
  65
  66 #define BALLOON_CLASS_NAME "xen_memory"
  67
  68 struct balloon_stats {
  69         /* We aim for 'current allocation' == 'target allocation'. */
  70         unsigned long current_pages;
  71         unsigned long target_pages;
  72         /*
  73          * Drivers may alter the memory reservation independently, but they
  74          * must inform the balloon driver so we avoid hitting the hard limit.
  75          */
  76         unsigned long driver_pages;
  77         /* Number of pages in high- and low-memory balloons. */
  78         unsigned long balloon_low;
  79         unsigned long balloon_high;
  80 };
  81
  82 static DEFINE_MUTEX(balloon_mutex);
  83
  84 static struct sys_device balloon_sysdev;
  85
  86 static int register_balloon(struct sys_device *sysdev);
  87
  88 static struct balloon_stats balloon_stats;
  89
  90 /* We increase/decrease in batches which fit in a page */
  91 static unsigned long frame_list[PAGE_SIZE / sizeof(unsigned long)];
  92
  93 #ifdef CONFIG_HIGHMEM
  94 #define inc_totalhigh_pages() (totalhigh_pages++)
  95 #define dec_totalhigh_pages() (totalhigh_pages--)
  96 #else
  97 #define inc_totalhigh_pages() do {} while(0)
  98 #define dec_totalhigh_pages() do {} while(0)
  99 #endif
 100
 101 /* List of ballooned pages, threaded through the mem_map array. */
 102 static LIST_HEAD(ballooned_pages);
 103
 104 /* Main work function, always executed in process context. */
 105 static void balloon_process(struct work_struct *work);
 106 static DECLARE_WORK(balloon_worker, balloon_process);
 107 static struct timer_list balloon_timer;
 108
 109 /* When ballooning out (allocating memory to return to Xen) we don't really
 110    want the kernel to try too hard since that can trigger the oom killer. */
 111 #define GFP_BALLOON \
 112         (GFP_HIGHUSER | __GFP_NOWARN | __GFP_NORETRY | __GFP_NOMEMALLOC)
 113
 114 static void scrub_page(struct page *page)
 115 {
 116 #ifdef CONFIG_XEN_SCRUB_PAGES
 117         clear_highpage(page);
 118 #endif
 119 }
 120
 121 /* balloon_append: add the given page to the balloon. */
 122 static void balloon_append(struct page *page)
 123 {
 124         /* Lowmem is re-populated first, so highmem pages go at list tail. */
 125         if (PageHighMem(page)) {
 126                 list_add_tail(&page->lru, &ballooned_pages);
 127                 balloon_stats.balloon_high++;
 128                 dec_totalhigh_pages();
 129         } else {
 130                 list_add(&page->lru, &ballooned_pages);
 131                 balloon_stats.balloon_low++;
 132         }
 133
 134         totalram_pages--;
 135 }
 136
 137 /* balloon_retrieve: rescue a page from the balloon, if it is not empty. */
 138 static struct page *balloon_retrieve(void)
 139 {
 140         struct page *page;
 141
 142         if (list_empty(&ballooned_pages))
 143                 return NULL;
 144
 145         page = list_entry(ballooned_pages.next, struct page, lru);
 146         list_del(&page->lru);
 147
 148         if (PageHighMem(page)) {
 149                 balloon_stats.balloon_high--;
 150                 inc_totalhigh_pages();
 151         }
 152         else
 153                 balloon_stats.balloon_low--;
 154
 155         totalram_pages++;
 156
 157         return page;
 158 }
 159
 160 static struct page *balloon_first_page(void)
 161 {
 162         if (list_empty(&ballooned_pages))
 163                 return NULL;
 164         return list_entry(ballooned_pages.next, struct page, lru);
 165 }
 166
 167 static struct page *balloon_next_page(struct page *page)
 168 {
 169         struct list_head *next = page->lru.next;
 170         if (next == &ballooned_pages)
 171                 return NULL;
 172         return list_entry(next, struct page, lru);
 173 }
 174
 175 static void balloon_alarm(unsigned long unused)
 176 {
 177         schedule_work(&balloon_worker);
 178 }
 179
 180 static unsigned long current_target(void)
 181 {
 182         unsigned long target = balloon_stats.target_pages;
 183
 184         target = min(target,
 185                      balloon_stats.current_pages +
 186                      balloon_stats.balloon_low +
 187                      balloon_stats.balloon_high);
 188
 189         return target;
 190 }
 191
 192 static int increase_reservation(unsigned long nr_pages)
 193 {
 194         unsigned long  pfn, i, flags;
 195         struct page   *page;
 196         long           rc;
 197         struct xen_memory_reservation reservation = {
 198                 .address_bits = 0,
 199                 .extent_order = 0,
 200                 .domid        = DOMID_SELF
 201         };
 202
 203         if (nr_pages > ARRAY_SIZE(frame_list))
 204                 nr_pages = ARRAY_SIZE(frame_list);
 205
 206         spin_lock_irqsave(&xen_reservation_lock, flags);
 207
 208         page = balloon_first_page();
 209         for (i = 0; i < nr_pages; i++) {
 210                 BUG_ON(page == NULL);
 211                 frame_list[i] = page_to_pfn(page);
 212                 page = balloon_next_page(page);
 213         }
 214
 215         set_xen_guest_handle(reservation.extent_start, frame_list);
 216         reservation.nr_extents = nr_pages;
 217         rc = HYPERVISOR_memory_op(XENMEM_populate_physmap, &reservation);
 218         if (rc < 0)
 219                 goto out;
 220
 221         for (i = 0; i < rc; i++) {
 222                 page = balloon_retrieve();
 223                 BUG_ON(page == NULL);
 224
 225                 pfn = page_to_pfn(page);
 226                 BUG_ON(!xen_feature(XENFEAT_auto_translated_physmap) &&
 227                        phys_to_machine_mapping_valid(pfn));
 228
 229                 set_phys_to_machine(pfn, frame_list[i]);
 230
 231                 /* Link back into the page tables if not highmem. */
 232                 if (pfn < max_low_pfn) {
 233                         int ret;
 234                         ret = HYPERVISOR_update_va_mapping(
 235                                 (unsigned long)__va(pfn << PAGE_SHIFT),
 236                                 mfn_pte(frame_list[i], PAGE_KERNEL),
 237                                 0);
 238                         BUG_ON(ret);
 239                 }
 240
 241                 /* Relinquish the page back to the allocator. */
 242                 ClearPageReserved(page);
 243                 init_page_count(page);
 244                 __free_page(page);
 245         }
 246
 247         balloon_stats.current_pages += rc;
 248
 249  out:
 250         spin_unlock_irqrestore(&xen_reservation_lock, flags);
 251
 252         return rc < 0 ? rc : rc != nr_pages;
 253 }
 254
 255 static int decrease_reservation(unsigned long nr_pages)
 256 {
 257         unsigned long  pfn, i, flags;
 258         struct page   *page;
 259         int            need_sleep = 0;
 260         int ret;
 261         struct xen_memory_reservation reservation = {
 262                 .address_bits = 0,
 263                 .extent_order = 0,
 264                 .domid        = DOMID_SELF
 265         };
 266
 267         if (nr_pages > ARRAY_SIZE(frame_list))
 268                 nr_pages = ARRAY_SIZE(frame_list);
 269
 270         for (i = 0; i < nr_pages; i++) {
 271                 if ((page = alloc_page(GFP_BALLOON)) == NULL) {
 272                         nr_pages = i;
 273                         need_sleep = 1;
 274                         break;
 275                 }
 276
 277                 pfn = page_to_pfn(page);
 278                 frame_list[i] = pfn_to_mfn(pfn);
 279
 280                 scrub_page(page);
 281
 282                 if (!PageHighMem(page)) {
 283                         ret = HYPERVISOR_update_va_mapping(
 284                                 (unsigned long)__va(pfn << PAGE_SHIFT),
 285                                 __pte_ma(0), 0);
 286                         BUG_ON(ret);
 287                 }
 288
 289         }
 290
 291         /* Ensure that ballooned highmem pages don't have kmaps. */
 292         kmap_flush_unused();
 293         flush_tlb_all();
 294
 295         spin_lock_irqsave(&xen_reservation_lock, flags);
 296
 297         /* No more mappings: invalidate P2M and add to balloon. */
 298         for (i = 0; i < nr_pages; i++) {
 299                 pfn = mfn_to_pfn(frame_list[i]);
 300                 set_phys_to_machine(pfn, INVALID_P2M_ENTRY);
 301                 balloon_append(pfn_to_page(pfn));
 302         }
 303
 304         set_xen_guest_handle(reservation.extent_start, frame_list);
 305         reservation.nr_extents   = nr_pages;
 306         ret = HYPERVISOR_memory_op(XENMEM_decrease_reservation, &reservation);
 307         BUG_ON(ret != nr_pages);
 308
 309         balloon_stats.current_pages -= nr_pages;
 310
 311         spin_unlock_irqrestore(&xen_reservation_lock, flags);
 312
 313         return need_sleep;
 314 }
 315
 316 /*
 317  * We avoid multiple worker processes conflicting via the balloon mutex.
 318  * We may of course race updates of the target counts (which are protected
 319  * by the balloon lock), or with changes to the Xen hard limit, but we will
 320  * recover from these in time.
 321  */
 322 static void balloon_process(struct work_struct *work)
 323 {
 324         int need_sleep = 0;
 325         long credit;
 326
 327         mutex_lock(&balloon_mutex);
 328
 329         do {
 330                 credit = current_target() - balloon_stats.current_pages;
 331                 if (credit > 0)
 332                         need_sleep = (increase_reservation(credit) != 0);
 333                 if (credit < 0)
 334                         need_sleep = (decrease_reservation(-credit) != 0);
 335
 336 #ifndef CONFIG_PREEMPT
 337                 if (need_resched())
 338                         schedule();
 339 #endif
 340         } while ((credit != 0) && !need_sleep);
 341
 342         /* Schedule more work if there is some still to be done. */
 343         if (current_target() != balloon_stats.current_pages)
 344                 mod_timer(&balloon_timer, jiffies + HZ);
 345
 346         mutex_unlock(&balloon_mutex);
 347 }
 348
 349 /* Resets the Xen limit, sets new target, and kicks off processing. */
 350 static void balloon_set_new_target(unsigned long target)
 351 {
 352         /* No need for lock. Not read-modify-write updates. */
 353         balloon_stats.target_pages = target;
 354         schedule_work(&balloon_worker);
 355 }
 356
 357 static struct xenbus_watch target_watch =
 358 {
 359         .node = "memory/target"
 360 };
 361
 362 /* React to a change in the target key */
 363 static void watch_target(struct xenbus_watch *watch,
 364                          const char **vec, unsigned int len)
 365 {
 366         unsigned long long new_target;
 367         int err;
 368
 369         err = xenbus_scanf(XBT_NIL, "memory", "target", "%llu", &new_target);
 370         if (err != 1) {
 371                 /* This is ok (for domain0 at least) - so just return */
 372                 return;
 373         }
 374
 375         /* The given memory/target value is in KiB, so it needs converting to
 376          * pages. PAGE_SHIFT converts bytes to pages, hence PAGE_SHIFT - 10.
 377          */
 378         balloon_set_new_target(new_target >> (PAGE_SHIFT - 10));
 379 }
 380
 381 static int balloon_init_watcher(struct notifier_block *notifier,
 382                                 unsigned long event,
 383                                 void *data)
 384 {
 385         int err;
 386
 387         err = register_xenbus_watch(&target_watch);
 388         if (err)
 389                 printk(KERN_ERR "Failed to set balloon watcher\n");
 390
 391         return NOTIFY_DONE;
 392 }
 393
 394 static struct notifier_block xenstore_notifier;
 395
 396 static int __init balloon_init(void)
 397 {
 398         unsigned long pfn;
 399         struct page *page;
 400
 401         if (!xen_pv_domain())
 402                 return -ENODEV;
 403
 404         pr_info("xen_balloon: Initialising balloon driver.\n");
 405
 406         balloon_stats.current_pages = min(xen_start_info->nr_pages, max_pfn);
 407         balloon_stats.target_pages  = balloon_stats.current_pages;
 408         balloon_stats.balloon_low   = 0;
 409         balloon_stats.balloon_high  = 0;
 410         balloon_stats.driver_pages  = 0UL;
 411
 412         init_timer(&balloon_timer);
 413         balloon_timer.data = 0;
 414         balloon_timer.function = balloon_alarm;
 415
 416         register_balloon(&balloon_sysdev);
 417
 418         /* Initialise the balloon with excess memory space. */
 419         for (pfn = xen_start_info->nr_pages; pfn < max_pfn; pfn++) {
 420                 page = pfn_to_page(pfn);
 421                 if (!PageReserved(page))
 422                         balloon_append(page);
 423         }
 424
 425         target_watch.callback = watch_target;
 426         xenstore_notifier.notifier_call = balloon_init_watcher;
 427
 428         register_xenstore_notifier(&xenstore_notifier);
 429
 430         return 0;
 431 }
 432
 433 subsys_initcall(balloon_init);
 434
 435 static void balloon_exit(void)
 436 {
 437     /* XXX - release balloon here */
 438     return;
 439 }
 440
 441 module_exit(balloon_exit);
 442
 443 #define BALLOON_SHOW(name, format, args...)                             \
 444         static ssize_t show_##name(struct sys_device *dev,              \
 445                                    struct sysdev_attribute *attr,       \
 446                                    char *buf)                           \
 447         {                                                               \
 448                 return sprintf(buf, format, ##args);                    \
 449         }                                                               \
 450         static SYSDEV_ATTR(name, S_IRUGO, show_##name, NULL)
 451
 452 BALLOON_SHOW(current_kb, "%lu\n", PAGES2KB(balloon_stats.current_pages));
 453 BALLOON_SHOW(low_kb, "%lu\n", PAGES2KB(balloon_stats.balloon_low));
 454 BALLOON_SHOW(high_kb, "%lu\n", PAGES2KB(balloon_stats.balloon_high));
 455 BALLOON_SHOW(driver_kb, "%lu\n", PAGES2KB(balloon_stats.driver_pages));
 456
 457 static ssize_t show_target_kb(struct sys_device *dev, struct sysdev_attribute *attr,
 458                               char *buf)
 459 {
 460         return sprintf(buf, "%lu\n", PAGES2KB(balloon_stats.target_pages));
 461 }
 462
 463 static ssize_t store_target_kb(struct sys_device *dev,
 464                                struct sysdev_attribute *attr,
 465                                const char *buf,
 466                                size_t count)
 467 {
 468         char *endchar;
 469         unsigned long long target_bytes;
 470
 471         if (!capable(CAP_SYS_ADMIN))
 472                 return -EPERM;
 473
 474         target_bytes = simple_strtoull(buf, &endchar, 0) * 1024;
 475
 476         balloon_set_new_target(target_bytes >> PAGE_SHIFT);
 477
 478         return count;
 479 }
 480
 481 static SYSDEV_ATTR(target_kb, S_IRUGO | S_IWUSR,
 482                    show_target_kb, store_target_kb);
 483
 484
 485 static ssize_t show_target(struct sys_device *dev, struct sysdev_attribute *attr,
 486                               char *buf)
 487 {
 488         return sprintf(buf, "%llu\n",
 489                        (unsigned long long)balloon_stats.target_pages
 490                        << PAGE_SHIFT);
 491 }
 492
 493 static ssize_t store_target(struct sys_device *dev,
 494                             struct sysdev_attribute *attr,
 495                             const char *buf,
 496                             size_t count)
 497 {
 498         char *endchar;
 499         unsigned long long target_bytes;
 500
 501         if (!capable(CAP_SYS_ADMIN))
 502                 return -EPERM;
 503
 504         target_bytes = memparse(buf, &endchar);
 505
 506         balloon_set_new_target(target_bytes >> PAGE_SHIFT);
 507
 508         return count;
 509 }
 510
 511 static SYSDEV_ATTR(target, S_IRUGO | S_IWUSR,
 512                    show_target, store_target);
 513
 514
 515 static struct sysdev_attribute *balloon_attrs[] = {
 516         &attr_target_kb,
 517         &attr_target,
 518 };
 519
 520 static struct attribute *balloon_info_attrs[] = {
 521         &attr_current_kb.attr,
 522         &attr_low_kb.attr,
 523         &attr_high_kb.attr,
 524         &attr_driver_kb.attr,
 525         NULL
 526 };
 527
 528 static struct attribute_group balloon_info_group = {
 529         .name = "info",
 530         .attrs = balloon_info_attrs,
 531 };
 532
 533 static struct sysdev_class balloon_sysdev_class = {
 534         .name = BALLOON_CLASS_NAME,
 535 };
 536
 537 static int register_balloon(struct sys_device *sysdev)
 538 {
 539         int i, error;
 540
 541         error = sysdev_class_register(&balloon_sysdev_class);
 542         if (error)
 543                 return error;
 544
 545         sysdev->id = 0;
 546         sysdev->cls = &balloon_sysdev_class;
 547
 548         error = sysdev_register(sysdev);
 549         if (error) {
 550                 sysdev_class_unregister(&balloon_sysdev_class);
 551                 return error;
 552         }
 553
 554         for (i = 0; i < ARRAY_SIZE(balloon_attrs); i++) {
 555                 error = sysdev_create_file(sysdev, balloon_attrs[i]);
 556                 if (error)
 557                         goto fail;
 558         }
 559
 560         error = sysfs_create_group(&sysdev->kobj, &balloon_info_group);
 561         if (error)
 562                 goto fail;
 563
 564         return 0;
 565
 566  fail:
 567         while (--i >= 0)
 568                 sysdev_remove_file(sysdev, balloon_attrs[i]);
 569         sysdev_unregister(sysdev);
 570         sysdev_class_unregister(&balloon_sysdev_class);
 571         return error;
 572 }
 573
 574 MODULE_LICENSE("GPL");