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