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