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   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/page.h>
  48 #include <asm/pgalloc.h>
  49 #include <asm/pgtable.h>
  50 #include <asm/uaccess.h>
  51 #include <asm/tlb.h>
  52
  53 #include <asm/xen/hypervisor.h>
  54 #include <asm/xen/hypercall.h>
  55 #include <xen/interface/xen.h>
  56 #include <xen/interface/memory.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 #ifdef CONFIG_HIGHMEM
 100 #define inc_totalhigh_pages() (totalhigh_pages++)
 101 #define dec_totalhigh_pages() (totalhigh_pages--)
 102 #else
 103 #define inc_totalhigh_pages() do {} while(0)
 104 #define dec_totalhigh_pages() do {} while(0)
 105 #endif
 106
 107 /* List of ballooned pages, threaded through the mem_map array. */
 108 static LIST_HEAD(ballooned_pages);
 109
 110 /* Main work function, always executed in process context. */
 111 static void balloon_process(struct work_struct *work);
 112 static DECLARE_WORK(balloon_worker, balloon_process);
 113 static struct timer_list balloon_timer;
 114
 115 /* When ballooning out (allocating memory to return to Xen) we don't really
 116    want the kernel to try too hard since that can trigger the oom killer. */
 117 #define GFP_BALLOON \
 118         (GFP_HIGHUSER | __GFP_NOWARN | __GFP_NORETRY | __GFP_NOMEMALLOC)
 119
 120 static void scrub_page(struct page *page)
 121 {
 122 #ifdef CONFIG_XEN_SCRUB_PAGES
 123         clear_highpage(page);
 124 #endif
 125 }
 126
 127 /* balloon_append: add the given page to the balloon. */
 128 static void balloon_append(struct page *page)
 129 {
 130         /* Lowmem is re-populated first, so highmem pages go at list tail. */
 131         if (PageHighMem(page)) {
 132                 list_add_tail(&page->lru, &ballooned_pages);
 133                 balloon_stats.balloon_high++;
 134                 dec_totalhigh_pages();
 135         } else {
 136                 list_add(&page->lru, &ballooned_pages);
 137                 balloon_stats.balloon_low++;
 138         }
 139 }
 140
 141 /* balloon_retrieve: rescue a page from the balloon, if it is not empty. */
 142 static struct page *balloon_retrieve(void)
 143 {
 144         struct page *page;
 145
 146         if (list_empty(&ballooned_pages))
 147                 return NULL;
 148
 149         page = list_entry(ballooned_pages.next, struct page, lru);
 150         list_del(&page->lru);
 151
 152         if (PageHighMem(page)) {
 153                 balloon_stats.balloon_high--;
 154                 inc_totalhigh_pages();
 155         }
 156         else
 157                 balloon_stats.balloon_low--;
 158
 159         return page;
 160 }
 161
 162 static struct page *balloon_first_page(void)
 163 {
 164         if (list_empty(&ballooned_pages))
 165                 return NULL;
 166         return list_entry(ballooned_pages.next, struct page, lru);
 167 }
 168
 169 static struct page *balloon_next_page(struct page *page)
 170 {
 171         struct list_head *next = page->lru.next;
 172         if (next == &ballooned_pages)
 173                 return NULL;
 174         return list_entry(next, struct page, lru);
 175 }
 176
 177 static void balloon_alarm(unsigned long unused)
 178 {
 179         schedule_work(&balloon_worker);
 180 }
 181
 182 static unsigned long current_target(void)
 183 {
 184         unsigned long target = min(balloon_stats.target_pages, balloon_stats.hard_limit);
 185
 186         target = min(target,
 187                      balloon_stats.current_pages +
 188                      balloon_stats.balloon_low +
 189                      balloon_stats.balloon_high);
 190
 191         return target;
 192 }
 193
 194 static int increase_reservation(unsigned long nr_pages)
 195 {
 196         unsigned long  pfn, i, flags;
 197         struct page   *page;
 198         long           rc;
 199         struct xen_memory_reservation reservation = {
 200                 .address_bits = 0,
 201                 .extent_order = 0,
 202                 .domid        = DOMID_SELF
 203         };
 204
 205         if (nr_pages > ARRAY_SIZE(frame_list))
 206                 nr_pages = ARRAY_SIZE(frame_list);
 207
 208         spin_lock_irqsave(&balloon_lock, flags);
 209
 210         page = balloon_first_page();
 211         for (i = 0; i < nr_pages; i++) {
 212                 BUG_ON(page == NULL);
 213                 frame_list[i] = page_to_pfn(page);
 214                 page = balloon_next_page(page);
 215         }
 216
 217         set_xen_guest_handle(reservation.extent_start, frame_list);
 218         reservation.nr_extents = nr_pages;
 219         rc = HYPERVISOR_memory_op(XENMEM_populate_physmap, &reservation);
 220         if (rc < nr_pages) {
 221                 if (rc > 0) {
 222                         int ret;
 223
 224                         /* We hit the Xen hard limit: reprobe. */
 225                         reservation.nr_extents = rc;
 226                         ret = HYPERVISOR_memory_op(XENMEM_decrease_reservation,
 227                                                    &reservation);
 228                         BUG_ON(ret != rc);
 229                 }
 230                 if (rc >= 0)
 231                         balloon_stats.hard_limit = (balloon_stats.current_pages + rc -
 232                                                     balloon_stats.driver_pages);
 233                 goto out;
 234         }
 235
 236         for (i = 0; i < nr_pages; i++) {
 237                 page = balloon_retrieve();
 238                 BUG_ON(page == NULL);
 239
 240                 pfn = page_to_pfn(page);
 241                 BUG_ON(!xen_feature(XENFEAT_auto_translated_physmap) &&
 242                        phys_to_machine_mapping_valid(pfn));
 243
 244                 set_phys_to_machine(pfn, frame_list[i]);
 245
 246                 /* Link back into the page tables if not highmem. */
 247                 if (pfn < max_low_pfn) {
 248                         int ret;
 249                         ret = HYPERVISOR_update_va_mapping(
 250                                 (unsigned long)__va(pfn << PAGE_SHIFT),
 251                                 mfn_pte(frame_list[i], PAGE_KERNEL),
 252                                 0);
 253                         BUG_ON(ret);
 254                 }
 255
 256                 /* Relinquish the page back to the allocator. */
 257                 ClearPageReserved(page);
 258                 init_page_count(page);
 259                 __free_page(page);
 260         }
 261
 262         balloon_stats.current_pages += nr_pages;
 263         totalram_pages = balloon_stats.current_pages;
 264
 265  out:
 266         spin_unlock_irqrestore(&balloon_lock, flags);
 267
 268         return 0;
 269 }
 270
 271 static int decrease_reservation(unsigned long nr_pages)
 272 {
 273         unsigned long  pfn, i, flags;
 274         struct page   *page;
 275         int            need_sleep = 0;
 276         int ret;
 277         struct xen_memory_reservation reservation = {
 278                 .address_bits = 0,
 279                 .extent_order = 0,
 280                 .domid        = DOMID_SELF
 281         };
 282
 283         if (nr_pages > ARRAY_SIZE(frame_list))
 284                 nr_pages = ARRAY_SIZE(frame_list);
 285
 286         for (i = 0; i < nr_pages; i++) {
 287                 if ((page = alloc_page(GFP_BALLOON)) == NULL) {
 288                         nr_pages = i;
 289                         need_sleep = 1;
 290                         break;
 291                 }
 292
 293                 pfn = page_to_pfn(page);
 294                 frame_list[i] = pfn_to_mfn(pfn);
 295
 296                 scrub_page(page);
 297
 298                 if (!PageHighMem(page)) {
 299                         ret = HYPERVISOR_update_va_mapping(
 300                                 (unsigned long)__va(pfn << PAGE_SHIFT),
 301                                 __pte_ma(0), 0);
 302                         BUG_ON(ret);
 303                 }
 304
 305         }
 306
 307         /* Ensure that ballooned highmem pages don't have kmaps. */
 308         kmap_flush_unused();
 309         flush_tlb_all();
 310
 311         spin_lock_irqsave(&balloon_lock, flags);
 312
 313         /* No more mappings: invalidate P2M and add to balloon. */
 314         for (i = 0; i < nr_pages; i++) {
 315                 pfn = mfn_to_pfn(frame_list[i]);
 316                 set_phys_to_machine(pfn, INVALID_P2M_ENTRY);
 317                 balloon_append(pfn_to_page(pfn));
 318         }
 319
 320         set_xen_guest_handle(reservation.extent_start, frame_list);
 321         reservation.nr_extents   = nr_pages;
 322         ret = HYPERVISOR_memory_op(XENMEM_decrease_reservation, &reservation);
 323         BUG_ON(ret != nr_pages);
 324
 325         balloon_stats.current_pages -= nr_pages;
 326         totalram_pages = balloon_stats.current_pages;
 327
 328         spin_unlock_irqrestore(&balloon_lock, flags);
 329
 330         return need_sleep;
 331 }
 332
 333 /*
 334  * We avoid multiple worker processes conflicting via the balloon mutex.
 335  * We may of course race updates of the target counts (which are protected
 336  * by the balloon lock), or with changes to the Xen hard limit, but we will
 337  * recover from these in time.
 338  */
 339 static void balloon_process(struct work_struct *work)
 340 {
 341         int need_sleep = 0;
 342         long credit;
 343
 344         mutex_lock(&balloon_mutex);
 345
 346         do {
 347                 credit = current_target() - balloon_stats.current_pages;
 348                 if (credit > 0)
 349                         need_sleep = (increase_reservation(credit) != 0);
 350                 if (credit < 0)
 351                         need_sleep = (decrease_reservation(-credit) != 0);
 352
 353 #ifndef CONFIG_PREEMPT
 354                 if (need_resched())
 355                         schedule();
 356 #endif
 357         } while ((credit != 0) && !need_sleep);
 358
 359         /* Schedule more work if there is some still to be done. */
 360         if (current_target() != balloon_stats.current_pages)
 361                 mod_timer(&balloon_timer, jiffies + HZ);
 362
 363         mutex_unlock(&balloon_mutex);
 364 }
 365
 366 /* Resets the Xen limit, sets new target, and kicks off processing. */
 367 static void balloon_set_new_target(unsigned long target)
 368 {
 369         /* No need for lock. Not read-modify-write updates. */
 370         balloon_stats.hard_limit   = ~0UL;
 371         balloon_stats.target_pages = target;
 372         schedule_work(&balloon_worker);
 373 }
 374
 375 static struct xenbus_watch target_watch =
 376 {
 377         .node = "memory/target"
 378 };
 379
 380 /* React to a change in the target key */
 381 static void watch_target(struct xenbus_watch *watch,
 382                          const char **vec, unsigned int len)
 383 {
 384         unsigned long long new_target;
 385         int err;
 386
 387         err = xenbus_scanf(XBT_NIL, "memory", "target", "%llu", &new_target);
 388         if (err != 1) {
 389                 /* This is ok (for domain0 at least) - so just return */
 390                 return;
 391         }
 392
 393         /* The given memory/target value is in KiB, so it needs converting to
 394          * pages. PAGE_SHIFT converts bytes to pages, hence PAGE_SHIFT - 10.
 395          */
 396         balloon_set_new_target(new_target >> (PAGE_SHIFT - 10));
 397 }
 398
 399 static int balloon_init_watcher(struct notifier_block *notifier,
 400                                 unsigned long event,
 401                                 void *data)
 402 {
 403         int err;
 404
 405         err = register_xenbus_watch(&target_watch);
 406         if (err)
 407                 printk(KERN_ERR "Failed to set balloon watcher\n");
 408
 409         return NOTIFY_DONE;
 410 }
 411
 412 static struct notifier_block xenstore_notifier;
 413
 414 static int __init balloon_init(void)
 415 {
 416         unsigned long pfn;
 417         struct page *page;
 418
 419         if (!xen_pv_domain())
 420                 return -ENODEV;
 421
 422         pr_info("xen_balloon: Initialising balloon driver.\n");
 423
 424         balloon_stats.current_pages = min(xen_start_info->nr_pages, max_pfn);
 425         totalram_pages   = balloon_stats.current_pages;
 426         balloon_stats.target_pages  = balloon_stats.current_pages;
 427         balloon_stats.balloon_low   = 0;
 428         balloon_stats.balloon_high  = 0;
 429         balloon_stats.driver_pages  = 0UL;
 430         balloon_stats.hard_limit    = ~0UL;
 431
 432         init_timer(&balloon_timer);
 433         balloon_timer.data = 0;
 434         balloon_timer.function = balloon_alarm;
 435
 436         register_balloon(&balloon_sysdev);
 437
 438         /* Initialise the balloon with excess memory space. */
 439         for (pfn = xen_start_info->nr_pages; pfn < max_pfn; pfn++) {
 440                 page = pfn_to_page(pfn);
 441                 if (!PageReserved(page))
 442                         balloon_append(page);
 443         }
 444
 445         target_watch.callback = watch_target;
 446         xenstore_notifier.notifier_call = balloon_init_watcher;
 447
 448         register_xenstore_notifier(&xenstore_notifier);
 449
 450         return 0;
 451 }
 452
 453 subsys_initcall(balloon_init);
 454
 455 static void balloon_exit(void)
 456 {
 457     /* XXX - release balloon here */
 458     return;
 459 }
 460
 461 module_exit(balloon_exit);
 462
 463 #define BALLOON_SHOW(name, format, args...)                             \
 464         static ssize_t show_##name(struct sys_device *dev,              \
 465                                    struct sysdev_attribute *attr,       \
 466                                    char *buf)                           \
 467         {                                                               \
 468                 return sprintf(buf, format, ##args);                    \
 469         }                                                               \
 470         static SYSDEV_ATTR(name, S_IRUGO, show_##name, NULL)
 471
 472 BALLOON_SHOW(current_kb, "%lu\n", PAGES2KB(balloon_stats.current_pages));
 473 BALLOON_SHOW(low_kb, "%lu\n", PAGES2KB(balloon_stats.balloon_low));
 474 BALLOON_SHOW(high_kb, "%lu\n", PAGES2KB(balloon_stats.balloon_high));
 475 BALLOON_SHOW(hard_limit_kb,
 476              (balloon_stats.hard_limit!=~0UL) ? "%lu\n" : "???\n",
 477              (balloon_stats.hard_limit!=~0UL) ? PAGES2KB(balloon_stats.hard_limit) : 0);
 478 BALLOON_SHOW(driver_kb, "%lu\n", PAGES2KB(balloon_stats.driver_pages));
 479
 480 static ssize_t show_target_kb(struct sys_device *dev, struct sysdev_attribute *attr,
 481                               char *buf)
 482 {
 483         return sprintf(buf, "%lu\n", PAGES2KB(balloon_stats.target_pages));
 484 }
 485
 486 static ssize_t store_target_kb(struct sys_device *dev,
 487                                struct sysdev_attribute *attr,
 488                                const char *buf,
 489                                size_t count)
 490 {
 491         char *endchar;
 492         unsigned long long target_bytes;
 493
 494         if (!capable(CAP_SYS_ADMIN))
 495                 return -EPERM;
 496
 497         target_bytes = simple_strtoull(buf, &endchar, 0) * 1024;
 498
 499         balloon_set_new_target(target_bytes >> PAGE_SHIFT);
 500
 501         return count;
 502 }
 503
 504 static SYSDEV_ATTR(target_kb, S_IRUGO | S_IWUSR,
 505                    show_target_kb, store_target_kb);
 506
 507
 508 static ssize_t show_target(struct sys_device *dev, struct sysdev_attribute *attr,
 509                               char *buf)
 510 {
 511         return sprintf(buf, "%llu\n",
 512                        (unsigned long long)balloon_stats.target_pages
 513                        << PAGE_SHIFT);
 514 }
 515
 516 static ssize_t store_target(struct sys_device *dev,
 517                             struct sysdev_attribute *attr,
 518                             const char *buf,
 519                             size_t count)
 520 {
 521         char *endchar;
 522         unsigned long long target_bytes;
 523
 524         if (!capable(CAP_SYS_ADMIN))
 525                 return -EPERM;
 526
 527         target_bytes = memparse(buf, &endchar);
 528
 529         balloon_set_new_target(target_bytes >> PAGE_SHIFT);
 530
 531         return count;
 532 }
 533
 534 static SYSDEV_ATTR(target, S_IRUGO | S_IWUSR,
 535                    show_target, store_target);
 536
 537
 538 static struct sysdev_attribute *balloon_attrs[] = {
 539         &attr_target_kb,
 540         &attr_target,
 541 };
 542
 543 static struct attribute *balloon_info_attrs[] = {
 544         &attr_current_kb.attr,
 545         &attr_low_kb.attr,
 546         &attr_high_kb.attr,
 547         &attr_hard_limit_kb.attr,
 548         &attr_driver_kb.attr,
 549         NULL
 550 };
 551
 552 static struct attribute_group balloon_info_group = {
 553         .name = "info",
 554         .attrs = balloon_info_attrs,
 555 };
 556
 557 static struct sysdev_class balloon_sysdev_class = {
 558         .name = BALLOON_CLASS_NAME,
 559 };
 560
 561 static int register_balloon(struct sys_device *sysdev)
 562 {
 563         int i, error;
 564
 565         error = sysdev_class_register(&balloon_sysdev_class);
 566         if (error)
 567                 return error;
 568
 569         sysdev->id = 0;
 570         sysdev->cls = &balloon_sysdev_class;
 571
 572         error = sysdev_register(sysdev);
 573         if (error) {
 574                 sysdev_class_unregister(&balloon_sysdev_class);
 575                 return error;
 576         }
 577
 578         for (i = 0; i < ARRAY_SIZE(balloon_attrs); i++) {
 579                 error = sysdev_create_file(sysdev, balloon_attrs[i]);
 580                 if (error)
 581                         goto fail;
 582         }
 583
 584         error = sysfs_create_group(&sysdev->kobj, &balloon_info_group);
 585         if (error)
 586                 goto fail;
 587
 588         return 0;
 589
 590  fail:
 591         while (--i >= 0)
 592                 sysdev_remove_file(sysdev, balloon_attrs[i]);
 593         sysdev_unregister(sysdev);
 594         sysdev_class_unregister(&balloon_sysdev_class);
 595         return error;
 596 }
 597
 598 MODULE_LICENSE("GPL");