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 /*
  89  * Protects atomic reservation decrease/increase against concurrent increases.
  90  * Also protects non-atomic updates of current_pages and driver_pages, and
  91  * balloon lists.
  92  */
  93 static DEFINE_SPINLOCK(balloon_lock);
  94
  95 static struct balloon_stats balloon_stats;
  96
  97 /* We increase/decrease in batches which fit in a page */
  98 static unsigned long frame_list[PAGE_SIZE / sizeof(unsigned long)];
  99
 100 #ifdef CONFIG_HIGHMEM
 101 #define inc_totalhigh_pages() (totalhigh_pages++)
 102 #define dec_totalhigh_pages() (totalhigh_pages--)
 103 #else
 104 #define inc_totalhigh_pages() do {} while(0)
 105 #define dec_totalhigh_pages() do {} while(0)
 106 #endif
 107
 108 /* List of ballooned pages, threaded through the mem_map array. */
 109 static LIST_HEAD(ballooned_pages);
 110
 111 /* Main work function, always executed in process context. */
 112 static void balloon_process(struct work_struct *work);
 113 static DECLARE_WORK(balloon_worker, balloon_process);
 114 static struct timer_list balloon_timer;
 115
 116 /* When ballooning out (allocating memory to return to Xen) we don't really
 117    want the kernel to try too hard since that can trigger the oom killer. */
 118 #define GFP_BALLOON \
 119         (GFP_HIGHUSER | __GFP_NOWARN | __GFP_NORETRY | __GFP_NOMEMALLOC)
 120
 121 static void scrub_page(struct page *page)
 122 {
 123 #ifdef CONFIG_XEN_SCRUB_PAGES
 124         clear_highpage(page);
 125 #endif
 126 }
 127
 128 /* balloon_append: add the given page to the balloon. */
 129 static void balloon_append(struct page *page)
 130 {
 131         /* Lowmem is re-populated first, so highmem pages go at list tail. */
 132         if (PageHighMem(page)) {
 133                 list_add_tail(&page->lru, &ballooned_pages);
 134                 balloon_stats.balloon_high++;
 135                 dec_totalhigh_pages();
 136         } else {
 137                 list_add(&page->lru, &ballooned_pages);
 138                 balloon_stats.balloon_low++;
 139         }
 140
 141         totalram_pages--;
 142 }
 143
 144 /* balloon_retrieve: rescue a page from the balloon, if it is not empty. */
 145 static struct page *balloon_retrieve(void)
 146 {
 147         struct page *page;
 148
 149         if (list_empty(&ballooned_pages))
 150                 return NULL;
 151
 152         page = list_entry(ballooned_pages.next, struct page, lru);
 153         list_del(&page->lru);
 154
 155         if (PageHighMem(page)) {
 156                 balloon_stats.balloon_high--;
 157                 inc_totalhigh_pages();
 158         }
 159         else
 160                 balloon_stats.balloon_low--;
 161
 162         totalram_pages++;
 163
 164         return page;
 165 }
 166
 167 static struct page *balloon_first_page(void)
 168 {
 169         if (list_empty(&ballooned_pages))
 170                 return NULL;
 171         return list_entry(ballooned_pages.next, struct page, lru);
 172 }
 173
 174 static struct page *balloon_next_page(struct page *page)
 175 {
 176         struct list_head *next = page->lru.next;
 177         if (next == &ballooned_pages)
 178                 return NULL;
 179         return list_entry(next, struct page, lru);
 180 }
 181
 182 static void balloon_alarm(unsigned long unused)
 183 {
 184         schedule_work(&balloon_worker);
 185 }
 186
 187 static unsigned long current_target(void)
 188 {
 189         unsigned long target = balloon_stats.target_pages;
 190
 191         target = min(target,
 192                      balloon_stats.current_pages +
 193                      balloon_stats.balloon_low +
 194                      balloon_stats.balloon_high);
 195
 196         return target;
 197 }
 198
 199 static int increase_reservation(unsigned long nr_pages)
 200 {
 201         unsigned long  pfn, i, flags;
 202         struct page   *page;
 203         long           rc;
 204         struct xen_memory_reservation reservation = {
 205                 .address_bits = 0,
 206                 .extent_order = 0,
 207                 .domid        = DOMID_SELF
 208         };
 209
 210         if (nr_pages > ARRAY_SIZE(frame_list))
 211                 nr_pages = ARRAY_SIZE(frame_list);
 212
 213         spin_lock_irqsave(&balloon_lock, flags);
 214
 215         page = balloon_first_page();
 216         for (i = 0; i < nr_pages; i++) {
 217                 BUG_ON(page == NULL);
 218                 frame_list[i] = page_to_pfn(page);
 219                 page = balloon_next_page(page);
 220         }
 221
 222         set_xen_guest_handle(reservation.extent_start, frame_list);
 223         reservation.nr_extents = nr_pages;
 224         rc = HYPERVISOR_memory_op(XENMEM_populate_physmap, &reservation);
 225         if (rc < 0)
 226                 goto out;
 227
 228         for (i = 0; i < rc; i++) {
 229                 page = balloon_retrieve();
 230                 BUG_ON(page == NULL);
 231
 232                 pfn = page_to_pfn(page);
 233                 BUG_ON(!xen_feature(XENFEAT_auto_translated_physmap) &&
 234                        phys_to_machine_mapping_valid(pfn));
 235
 236                 set_phys_to_machine(pfn, frame_list[i]);
 237
 238                 /* Link back into the page tables if not highmem. */
 239                 if (pfn < max_low_pfn) {
 240                         int ret;
 241                         ret = HYPERVISOR_update_va_mapping(
 242                                 (unsigned long)__va(pfn << PAGE_SHIFT),
 243                                 mfn_pte(frame_list[i], PAGE_KERNEL),
 244                                 0);
 245                         BUG_ON(ret);
 246                 }
 247
 248                 /* Relinquish the page back to the allocator. */
 249                 ClearPageReserved(page);
 250                 init_page_count(page);
 251                 __free_page(page);
 252         }
 253
 254         balloon_stats.current_pages += rc;
 255
 256  out:
 257         spin_unlock_irqrestore(&balloon_lock, flags);
 258
 259         return rc < 0 ? rc : rc != nr_pages;
 260 }
 261
 262 static int decrease_reservation(unsigned long nr_pages)
 263 {
 264         unsigned long  pfn, i, flags;
 265         struct page   *page;
 266         int            need_sleep = 0;
 267         int ret;
 268         struct xen_memory_reservation reservation = {
 269                 .address_bits = 0,
 270                 .extent_order = 0,
 271                 .domid        = DOMID_SELF
 272         };
 273
 274         if (nr_pages > ARRAY_SIZE(frame_list))
 275                 nr_pages = ARRAY_SIZE(frame_list);
 276
 277         for (i = 0; i < nr_pages; i++) {
 278                 if ((page = alloc_page(GFP_BALLOON)) == NULL) {
 279                         nr_pages = i;
 280                         need_sleep = 1;
 281                         break;
 282                 }
 283
 284                 pfn = page_to_pfn(page);
 285                 frame_list[i] = pfn_to_mfn(pfn);
 286
 287                 scrub_page(page);
 288
 289                 if (!PageHighMem(page)) {
 290                         ret = HYPERVISOR_update_va_mapping(
 291                                 (unsigned long)__va(pfn << PAGE_SHIFT),
 292                                 __pte_ma(0), 0);
 293                         BUG_ON(ret);
 294                 }
 295
 296         }
 297
 298         /* Ensure that ballooned highmem pages don't have kmaps. */
 299         kmap_flush_unused();
 300         flush_tlb_all();
 301
 302         spin_lock_irqsave(&balloon_lock, flags);
 303
 304         /* No more mappings: invalidate P2M and add to balloon. */
 305         for (i = 0; i < nr_pages; i++) {
 306                 pfn = mfn_to_pfn(frame_list[i]);
 307                 set_phys_to_machine(pfn, INVALID_P2M_ENTRY);
 308                 balloon_append(pfn_to_page(pfn));
 309         }
 310
 311         set_xen_guest_handle(reservation.extent_start, frame_list);
 312         reservation.nr_extents   = nr_pages;
 313         ret = HYPERVISOR_memory_op(XENMEM_decrease_reservation, &reservation);
 314         BUG_ON(ret != nr_pages);
 315
 316         balloon_stats.current_pages -= nr_pages;
 317
 318         spin_unlock_irqrestore(&balloon_lock, flags);
 319
 320         return need_sleep;
 321 }
 322
 323 /*
 324  * We avoid multiple worker processes conflicting via the balloon mutex.
 325  * We may of course race updates of the target counts (which are protected
 326  * by the balloon lock), or with changes to the Xen hard limit, but we will
 327  * recover from these in time.
 328  */
 329 static void balloon_process(struct work_struct *work)
 330 {
 331         int need_sleep = 0;
 332         long credit;
 333
 334         mutex_lock(&balloon_mutex);
 335
 336         do {
 337                 credit = current_target() - balloon_stats.current_pages;
 338                 if (credit > 0)
 339                         need_sleep = (increase_reservation(credit) != 0);
 340                 if (credit < 0)
 341                         need_sleep = (decrease_reservation(-credit) != 0);
 342
 343 #ifndef CONFIG_PREEMPT
 344                 if (need_resched())
 345                         schedule();
 346 #endif
 347         } while ((credit != 0) && !need_sleep);
 348
 349         /* Schedule more work if there is some still to be done. */
 350         if (current_target() != balloon_stats.current_pages)
 351                 mod_timer(&balloon_timer, jiffies + HZ);
 352
 353         mutex_unlock(&balloon_mutex);
 354 }
 355
 356 /* Resets the Xen limit, sets new target, and kicks off processing. */
 357 static void balloon_set_new_target(unsigned long target)
 358 {
 359         /* No need for lock. Not read-modify-write updates. */
 360         balloon_stats.target_pages = target;
 361         schedule_work(&balloon_worker);
 362 }
 363
 364 static struct xenbus_watch target_watch =
 365 {
 366         .node = "memory/target"
 367 };
 368
 369 /* React to a change in the target key */
 370 static void watch_target(struct xenbus_watch *watch,
 371                          const char **vec, unsigned int len)
 372 {
 373         unsigned long long new_target;
 374         int err;
 375
 376         err = xenbus_scanf(XBT_NIL, "memory", "target", "%llu", &new_target);
 377         if (err != 1) {
 378                 /* This is ok (for domain0 at least) - so just return */
 379                 return;
 380         }
 381
 382         /* The given memory/target value is in KiB, so it needs converting to
 383          * pages. PAGE_SHIFT converts bytes to pages, hence PAGE_SHIFT - 10.
 384          */
 385         balloon_set_new_target(new_target >> (PAGE_SHIFT - 10));
 386 }
 387
 388 static int balloon_init_watcher(struct notifier_block *notifier,
 389                                 unsigned long event,
 390                                 void *data)
 391 {
 392         int err;
 393
 394         err = register_xenbus_watch(&target_watch);
 395         if (err)
 396                 printk(KERN_ERR "Failed to set balloon watcher\n");
 397
 398         return NOTIFY_DONE;
 399 }
 400
 401 static struct notifier_block xenstore_notifier;
 402
 403 static int __init balloon_init(void)
 404 {
 405         unsigned long pfn;
 406         struct page *page;
 407
 408         if (!xen_pv_domain())
 409                 return -ENODEV;
 410
 411         pr_info("xen_balloon: Initialising balloon driver.\n");
 412
 413         balloon_stats.current_pages = min(xen_start_info->nr_pages, max_pfn);
 414         balloon_stats.target_pages  = balloon_stats.current_pages;
 415         balloon_stats.balloon_low   = 0;
 416         balloon_stats.balloon_high  = 0;
 417         balloon_stats.driver_pages  = 0UL;
 418
 419         init_timer(&balloon_timer);
 420         balloon_timer.data = 0;
 421         balloon_timer.function = balloon_alarm;
 422
 423         register_balloon(&balloon_sysdev);
 424
 425         /* Initialise the balloon with excess memory space. */
 426         for (pfn = xen_start_info->nr_pages; pfn < max_pfn; pfn++) {
 427                 page = pfn_to_page(pfn);
 428                 if (!PageReserved(page))
 429                         balloon_append(page);
 430         }
 431
 432         target_watch.callback = watch_target;
 433         xenstore_notifier.notifier_call = balloon_init_watcher;
 434
 435         register_xenstore_notifier(&xenstore_notifier);
 436
 437         return 0;
 438 }
 439
 440 subsys_initcall(balloon_init);
 441
 442 static void balloon_exit(void)
 443 {
 444     /* XXX - release balloon here */
 445     return;
 446 }
 447
 448 module_exit(balloon_exit);
 449
 450 #define BALLOON_SHOW(name, format, args...)                             \
 451         static ssize_t show_##name(struct sys_device *dev,              \
 452                                    struct sysdev_attribute *attr,       \
 453                                    char *buf)                           \
 454         {                                                               \
 455                 return sprintf(buf, format, ##args);                    \
 456         }                                                               \
 457         static SYSDEV_ATTR(name, S_IRUGO, show_##name, NULL)
 458
 459 BALLOON_SHOW(current_kb, "%lu\n", PAGES2KB(balloon_stats.current_pages));
 460 BALLOON_SHOW(low_kb, "%lu\n", PAGES2KB(balloon_stats.balloon_low));
 461 BALLOON_SHOW(high_kb, "%lu\n", PAGES2KB(balloon_stats.balloon_high));
 462 BALLOON_SHOW(driver_kb, "%lu\n", PAGES2KB(balloon_stats.driver_pages));
 463
 464 static ssize_t show_target_kb(struct sys_device *dev, struct sysdev_attribute *attr,
 465                               char *buf)
 466 {
 467         return sprintf(buf, "%lu\n", PAGES2KB(balloon_stats.target_pages));
 468 }
 469
 470 static ssize_t store_target_kb(struct sys_device *dev,
 471                                struct sysdev_attribute *attr,
 472                                const char *buf,
 473                                size_t count)
 474 {
 475         char *endchar;
 476         unsigned long long target_bytes;
 477
 478         if (!capable(CAP_SYS_ADMIN))
 479                 return -EPERM;
 480
 481         target_bytes = simple_strtoull(buf, &endchar, 0) * 1024;
 482
 483         balloon_set_new_target(target_bytes >> PAGE_SHIFT);
 484
 485         return count;
 486 }
 487
 488 static SYSDEV_ATTR(target_kb, S_IRUGO | S_IWUSR,
 489                    show_target_kb, store_target_kb);
 490
 491
 492 static ssize_t show_target(struct sys_device *dev, struct sysdev_attribute *attr,
 493                               char *buf)
 494 {
 495         return sprintf(buf, "%llu\n",
 496                        (unsigned long long)balloon_stats.target_pages
 497                        << PAGE_SHIFT);
 498 }
 499
 500 static ssize_t store_target(struct sys_device *dev,
 501                             struct sysdev_attribute *attr,
 502                             const char *buf,
 503                             size_t count)
 504 {
 505         char *endchar;
 506         unsigned long long target_bytes;
 507
 508         if (!capable(CAP_SYS_ADMIN))
 509                 return -EPERM;
 510
 511         target_bytes = memparse(buf, &endchar);
 512
 513         balloon_set_new_target(target_bytes >> PAGE_SHIFT);
 514
 515         return count;
 516 }
 517
 518 static SYSDEV_ATTR(target, S_IRUGO | S_IWUSR,
 519                    show_target, store_target);
 520
 521
 522 static struct sysdev_attribute *balloon_attrs[] = {
 523         &attr_target_kb,
 524         &attr_target,
 525 };
 526
 527 static struct attribute *balloon_info_attrs[] = {
 528         &attr_current_kb.attr,
 529         &attr_low_kb.attr,
 530         &attr_high_kb.attr,
 531         &attr_driver_kb.attr,
 532         NULL
 533 };
 534
 535 static struct attribute_group balloon_info_group = {
 536         .name = "info",
 537         .attrs = balloon_info_attrs,
 538 };
 539
 540 static struct sysdev_class balloon_sysdev_class = {
 541         .name = BALLOON_CLASS_NAME,
 542 };
 543
 544 static int register_balloon(struct sys_device *sysdev)
 545 {
 546         int i, error;
 547
 548         error = sysdev_class_register(&balloon_sysdev_class);
 549         if (error)
 550                 return error;
 551
 552         sysdev->id = 0;
 553         sysdev->cls = &balloon_sysdev_class;
 554
 555         error = sysdev_register(sysdev);
 556         if (error) {
 557                 sysdev_class_unregister(&balloon_sysdev_class);
 558                 return error;
 559         }
 560
 561         for (i = 0; i < ARRAY_SIZE(balloon_attrs); i++) {
 562                 error = sysdev_create_file(sysdev, balloon_attrs[i]);
 563                 if (error)
 564                         goto fail;
 565         }
 566
 567         error = sysfs_create_group(&sysdev->kobj, &balloon_info_group);
 568         if (error)
 569                 goto fail;
 570
 571         return 0;
 572
 573  fail:
 574         while (--i >= 0)
 575                 sysdev_remove_file(sysdev, balloon_attrs[i]);
 576         sysdev_unregister(sysdev);
 577         sysdev_class_unregister(&balloon_sysdev_class);
 578         return error;
 579 }
 580
 581 MODULE_LICENSE("GPL");