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 #include <asm/e820.h>
  54
  55 #include <asm/xen/hypervisor.h>
  56 #include <asm/xen/hypercall.h>
  57
  58 #include <xen/xen.h>
  59 #include <xen/interface/xen.h>
  60 #include <xen/interface/memory.h>
  61 #include <xen/xenbus.h>
  62 #include <xen/features.h>
  63 #include <xen/page.h>
  64
  65 #define PAGES2KB(_p) ((_p)<<(PAGE_SHIFT-10))
  66
  67 #define BALLOON_CLASS_NAME "xen_memory"
  68
  69 struct balloon_stats {
  70         /* We aim for 'current allocation' == 'target allocation'. */
  71         unsigned long current_pages;
  72         unsigned long target_pages;
  73         /*
  74          * Drivers may alter the memory reservation independently, but they
  75          * must inform the balloon driver so we avoid hitting the hard limit.
  76          */
  77         unsigned long driver_pages;
  78         /* Number of pages in high- and low-memory balloons. */
  79         unsigned long balloon_low;
  80         unsigned long balloon_high;
  81 };
  82
  83 static DEFINE_MUTEX(balloon_mutex);
  84
  85 static struct sys_device balloon_sysdev;
  86
  87 static int register_balloon(struct sys_device *sysdev);
  88
  89 static struct balloon_stats balloon_stats;
  90
  91 /* We increase/decrease in batches which fit in a page */
  92 static unsigned long frame_list[PAGE_SIZE / sizeof(unsigned long)];
  93
  94 #ifdef CONFIG_HIGHMEM
  95 #define inc_totalhigh_pages() (totalhigh_pages++)
  96 #define dec_totalhigh_pages() (totalhigh_pages--)
  97 #else
  98 #define inc_totalhigh_pages() do {} while(0)
  99 #define dec_totalhigh_pages() do {} while(0)
 100 #endif
 101
 102 /* List of ballooned pages, threaded through the mem_map array. */
 103 static LIST_HEAD(ballooned_pages);
 104
 105 /* Main work function, always executed in process context. */
 106 static void balloon_process(struct work_struct *work);
 107 static DECLARE_WORK(balloon_worker, balloon_process);
 108 static struct timer_list balloon_timer;
 109
 110 /* When ballooning out (allocating memory to return to Xen) we don't really
 111    want the kernel to try too hard since that can trigger the oom killer. */
 112 #define GFP_BALLOON \
 113         (GFP_HIGHUSER | __GFP_NOWARN | __GFP_NORETRY | __GFP_NOMEMALLOC)
 114
 115 static void scrub_page(struct page *page)
 116 {
 117 #ifdef CONFIG_XEN_SCRUB_PAGES
 118         clear_highpage(page);
 119 #endif
 120 }
 121
 122 /* balloon_append: add the given page to the balloon. */
 123 static void __balloon_append(struct page *page)
 124 {
 125         /* Lowmem is re-populated first, so highmem pages go at list tail. */
 126         if (PageHighMem(page)) {
 127                 list_add_tail(&page->lru, &ballooned_pages);
 128                 balloon_stats.balloon_high++;
 129                 dec_totalhigh_pages();
 130         } else {
 131                 list_add(&page->lru, &ballooned_pages);
 132                 balloon_stats.balloon_low++;
 133         }
 134 }
 135
 136 static void balloon_append(struct page *page)
 137 {
 138         __balloon_append(page);
 139         totalram_pages--;
 140 }
 141
 142 /* balloon_retrieve: rescue a page from the balloon, if it is not empty. */
 143 static struct page *balloon_retrieve(void)
 144 {
 145         struct page *page;
 146
 147         if (list_empty(&ballooned_pages))
 148                 return NULL;
 149
 150         page = list_entry(ballooned_pages.next, struct page, lru);
 151         list_del(&page->lru);
 152
 153         if (PageHighMem(page)) {
 154                 balloon_stats.balloon_high--;
 155                 inc_totalhigh_pages();
 156         }
 157         else
 158                 balloon_stats.balloon_low--;
 159
 160         totalram_pages++;
 161
 162         return page;
 163 }
 164
 165 static struct page *balloon_first_page(void)
 166 {
 167         if (list_empty(&ballooned_pages))
 168                 return NULL;
 169         return list_entry(ballooned_pages.next, struct page, lru);
 170 }
 171
 172 static struct page *balloon_next_page(struct page *page)
 173 {
 174         struct list_head *next = page->lru.next;
 175         if (next == &ballooned_pages)
 176                 return NULL;
 177         return list_entry(next, struct page, lru);
 178 }
 179
 180 static void balloon_alarm(unsigned long unused)
 181 {
 182         schedule_work(&balloon_worker);
 183 }
 184
 185 static unsigned long current_target(void)
 186 {
 187         unsigned long target = balloon_stats.target_pages;
 188
 189         target = min(target,
 190                      balloon_stats.current_pages +
 191                      balloon_stats.balloon_low +
 192                      balloon_stats.balloon_high);
 193
 194         return target;
 195 }
 196
 197 static int increase_reservation(unsigned long nr_pages)
 198 {
 199         unsigned long  pfn, i;
 200         struct page   *page;
 201         long           rc;
 202         struct xen_memory_reservation reservation = {
 203                 .address_bits = 0,
 204                 .extent_order = 0,
 205                 .domid        = DOMID_SELF
 206         };
 207
 208         if (nr_pages > ARRAY_SIZE(frame_list))
 209                 nr_pages = ARRAY_SIZE(frame_list);
 210
 211         page = balloon_first_page();
 212         for (i = 0; i < nr_pages; i++) {
 213                 BUG_ON(page == NULL);
 214                 frame_list[i] = page_to_pfn(page);
 215                 page = balloon_next_page(page);
 216         }
 217
 218         set_xen_guest_handle(reservation.extent_start, frame_list);
 219         reservation.nr_extents = nr_pages;
 220         rc = HYPERVISOR_memory_op(XENMEM_populate_physmap, &reservation);
 221         if (rc < 0)
 222                 goto out;
 223
 224         for (i = 0; i < rc; i++) {
 225                 page = balloon_retrieve();
 226                 BUG_ON(page == NULL);
 227
 228                 pfn = page_to_pfn(page);
 229                 BUG_ON(!xen_feature(XENFEAT_auto_translated_physmap) &&
 230                        phys_to_machine_mapping_valid(pfn));
 231
 232                 set_phys_to_machine(pfn, frame_list[i]);
 233
 234                 /* Link back into the page tables if not highmem. */
 235                 if (pfn < max_low_pfn) {
 236                         int ret;
 237                         ret = HYPERVISOR_update_va_mapping(
 238                                 (unsigned long)__va(pfn << PAGE_SHIFT),
 239                                 mfn_pte(frame_list[i], PAGE_KERNEL),
 240                                 0);
 241                         BUG_ON(ret);
 242                 }
 243
 244                 /* Relinquish the page back to the allocator. */
 245                 ClearPageReserved(page);
 246                 init_page_count(page);
 247                 __free_page(page);
 248         }
 249
 250         balloon_stats.current_pages += rc;
 251
 252  out:
 253         return rc < 0 ? rc : rc != nr_pages;
 254 }
 255
 256 static int decrease_reservation(unsigned long nr_pages)
 257 {
 258         unsigned long  pfn, i;
 259         struct page   *page;
 260         int            need_sleep = 0;
 261         int ret;
 262         struct xen_memory_reservation reservation = {
 263                 .address_bits = 0,
 264                 .extent_order = 0,
 265                 .domid        = DOMID_SELF
 266         };
 267
 268         if (nr_pages > ARRAY_SIZE(frame_list))
 269                 nr_pages = ARRAY_SIZE(frame_list);
 270
 271         for (i = 0; i < nr_pages; i++) {
 272                 if ((page = alloc_page(GFP_BALLOON)) == NULL) {
 273                         nr_pages = i;
 274                         need_sleep = 1;
 275                         break;
 276                 }
 277
 278                 pfn = page_to_pfn(page);
 279                 frame_list[i] = pfn_to_mfn(pfn);
 280
 281                 scrub_page(page);
 282
 283                 if (!PageHighMem(page)) {
 284                         ret = HYPERVISOR_update_va_mapping(
 285                                 (unsigned long)__va(pfn << PAGE_SHIFT),
 286                                 __pte_ma(0), 0);
 287                         BUG_ON(ret);
 288                 }
 289
 290         }
 291
 292         /* Ensure that ballooned highmem pages don't have kmaps. */
 293         kmap_flush_unused();
 294         flush_tlb_all();
 295
 296         /* No more mappings: invalidate P2M and add to balloon. */
 297         for (i = 0; i < nr_pages; i++) {
 298                 pfn = mfn_to_pfn(frame_list[i]);
 299                 set_phys_to_machine(pfn, INVALID_P2M_ENTRY);
 300                 balloon_append(pfn_to_page(pfn));
 301         }
 302
 303         set_xen_guest_handle(reservation.extent_start, frame_list);
 304         reservation.nr_extents   = nr_pages;
 305         ret = HYPERVISOR_memory_op(XENMEM_decrease_reservation, &reservation);
 306         BUG_ON(ret != nr_pages);
 307
 308         balloon_stats.current_pages -= nr_pages;
 309
 310         return need_sleep;
 311 }
 312
 313 /*
 314  * We avoid multiple worker processes conflicting via the balloon mutex.
 315  * We may of course race updates of the target counts (which are protected
 316  * by the balloon lock), or with changes to the Xen hard limit, but we will
 317  * recover from these in time.
 318  */
 319 static void balloon_process(struct work_struct *work)
 320 {
 321         int need_sleep = 0;
 322         long credit;
 323
 324         mutex_lock(&balloon_mutex);
 325
 326         do {
 327                 credit = current_target() - balloon_stats.current_pages;
 328                 if (credit > 0)
 329                         need_sleep = (increase_reservation(credit) != 0);
 330                 if (credit < 0)
 331                         need_sleep = (decrease_reservation(-credit) != 0);
 332
 333 #ifndef CONFIG_PREEMPT
 334                 if (need_resched())
 335                         schedule();
 336 #endif
 337         } while ((credit != 0) && !need_sleep);
 338
 339         /* Schedule more work if there is some still to be done. */
 340         if (current_target() != balloon_stats.current_pages)
 341                 mod_timer(&balloon_timer, jiffies + HZ);
 342
 343         mutex_unlock(&balloon_mutex);
 344 }
 345
 346 /* Resets the Xen limit, sets new target, and kicks off processing. */
 347 static void balloon_set_new_target(unsigned long target)
 348 {
 349         /* No need for lock. Not read-modify-write updates. */
 350         balloon_stats.target_pages = target;
 351         schedule_work(&balloon_worker);
 352 }
 353
 354 static struct xenbus_watch target_watch =
 355 {
 356         .node = "memory/target"
 357 };
 358
 359 /* React to a change in the target key */
 360 static void watch_target(struct xenbus_watch *watch,
 361                          const char **vec, unsigned int len)
 362 {
 363         unsigned long long new_target;
 364         int err;
 365
 366         err = xenbus_scanf(XBT_NIL, "memory", "target", "%llu", &new_target);
 367         if (err != 1) {
 368                 /* This is ok (for domain0 at least) - so just return */
 369                 return;
 370         }
 371
 372         /* The given memory/target value is in KiB, so it needs converting to
 373          * pages. PAGE_SHIFT converts bytes to pages, hence PAGE_SHIFT - 10.
 374          */
 375         balloon_set_new_target(new_target >> (PAGE_SHIFT - 10));
 376 }
 377
 378 static int balloon_init_watcher(struct notifier_block *notifier,
 379                                 unsigned long event,
 380                                 void *data)
 381 {
 382         int err;
 383
 384         err = register_xenbus_watch(&target_watch);
 385         if (err)
 386                 printk(KERN_ERR "Failed to set balloon watcher\n");
 387
 388         return NOTIFY_DONE;
 389 }
 390
 391 static struct notifier_block xenstore_notifier;
 392
 393 static int __init balloon_init(void)
 394 {
 395         unsigned long pfn, extra_pfn_end;
 396         struct page *page;
 397
 398         if (!xen_pv_domain())
 399                 return -ENODEV;
 400
 401         pr_info("xen_balloon: Initialising balloon driver.\n");
 402
 403         balloon_stats.current_pages = min(xen_start_info->nr_pages, max_pfn);
 404         balloon_stats.target_pages  = balloon_stats.current_pages;
 405         balloon_stats.balloon_low   = 0;
 406         balloon_stats.balloon_high  = 0;
 407         balloon_stats.driver_pages  = 0UL;
 408
 409         init_timer(&balloon_timer);
 410         balloon_timer.data = 0;
 411         balloon_timer.function = balloon_alarm;
 412
 413         register_balloon(&balloon_sysdev);
 414
 415         /* Initialise the balloon with excess memory space. */
 416         extra_pfn_end = min(e820_end_of_ram_pfn(),
 417                             (unsigned long)PFN_DOWN(xen_extra_mem_start + xen_extra_mem_size));
 418         for (pfn = PFN_UP(xen_extra_mem_start);
 419              pfn < extra_pfn_end;
 420              pfn++) {
 421                 page = pfn_to_page(pfn);
 422                 /* totalram_pages doesn't include the boot-time
 423                    balloon extension, so don't subtract from it. */
 424                 __balloon_append(page);
 425         }
 426
 427         target_watch.callback = watch_target;
 428         xenstore_notifier.notifier_call = balloon_init_watcher;
 429
 430         register_xenstore_notifier(&xenstore_notifier);
 431
 432         return 0;
 433 }
 434
 435 subsys_initcall(balloon_init);
 436
 437 static void balloon_exit(void)
 438 {
 439     /* XXX - release balloon here */
 440     return;
 441 }
 442
 443 module_exit(balloon_exit);
 444
 445 #define BALLOON_SHOW(name, format, args...)                             \
 446         static ssize_t show_##name(struct sys_device *dev,              \
 447                                    struct sysdev_attribute *attr,       \
 448                                    char *buf)                           \
 449         {                                                               \
 450                 return sprintf(buf, format, ##args);                    \
 451         }                                                               \
 452         static SYSDEV_ATTR(name, S_IRUGO, show_##name, NULL)
 453
 454 BALLOON_SHOW(current_kb, "%lu\n", PAGES2KB(balloon_stats.current_pages));
 455 BALLOON_SHOW(low_kb, "%lu\n", PAGES2KB(balloon_stats.balloon_low));
 456 BALLOON_SHOW(high_kb, "%lu\n", PAGES2KB(balloon_stats.balloon_high));
 457 BALLOON_SHOW(driver_kb, "%lu\n", PAGES2KB(balloon_stats.driver_pages));
 458
 459 static ssize_t show_target_kb(struct sys_device *dev, struct sysdev_attribute *attr,
 460                               char *buf)
 461 {
 462         return sprintf(buf, "%lu\n", PAGES2KB(balloon_stats.target_pages));
 463 }
 464
 465 static ssize_t store_target_kb(struct sys_device *dev,
 466                                struct sysdev_attribute *attr,
 467                                const char *buf,
 468                                size_t count)
 469 {
 470         char *endchar;
 471         unsigned long long target_bytes;
 472
 473         if (!capable(CAP_SYS_ADMIN))
 474                 return -EPERM;
 475
 476         target_bytes = simple_strtoull(buf, &endchar, 0) * 1024;
 477
 478         balloon_set_new_target(target_bytes >> PAGE_SHIFT);
 479
 480         return count;
 481 }
 482
 483 static SYSDEV_ATTR(target_kb, S_IRUGO | S_IWUSR,
 484                    show_target_kb, store_target_kb);
 485
 486
 487 static ssize_t show_target(struct sys_device *dev, struct sysdev_attribute *attr,
 488                               char *buf)
 489 {
 490         return sprintf(buf, "%llu\n",
 491                        (unsigned long long)balloon_stats.target_pages
 492                        << PAGE_SHIFT);
 493 }
 494
 495 static ssize_t store_target(struct sys_device *dev,
 496                             struct sysdev_attribute *attr,
 497                             const char *buf,
 498                             size_t count)
 499 {
 500         char *endchar;
 501         unsigned long long target_bytes;
 502
 503         if (!capable(CAP_SYS_ADMIN))
 504                 return -EPERM;
 505
 506         target_bytes = memparse(buf, &endchar);
 507
 508         balloon_set_new_target(target_bytes >> PAGE_SHIFT);
 509
 510         return count;
 511 }
 512
 513 static SYSDEV_ATTR(target, S_IRUGO | S_IWUSR,
 514                    show_target, store_target);
 515
 516
 517 static struct sysdev_attribute *balloon_attrs[] = {
 518         &attr_target_kb,
 519         &attr_target,
 520 };
 521
 522 static struct attribute *balloon_info_attrs[] = {
 523         &attr_current_kb.attr,
 524         &attr_low_kb.attr,
 525         &attr_high_kb.attr,
 526         &attr_driver_kb.attr,
 527         NULL
 528 };
 529
 530 static struct attribute_group balloon_info_group = {
 531         .name = "info",
 532         .attrs = balloon_info_attrs,
 533 };
 534
 535 static struct sysdev_class balloon_sysdev_class = {
 536         .name = BALLOON_CLASS_NAME,
 537 };
 538
 539 static int register_balloon(struct sys_device *sysdev)
 540 {
 541         int i, error;
 542
 543         error = sysdev_class_register(&balloon_sysdev_class);
 544         if (error)
 545                 return error;
 546
 547         sysdev->id = 0;
 548         sysdev->cls = &balloon_sysdev_class;
 549
 550         error = sysdev_register(sysdev);
 551         if (error) {
 552                 sysdev_class_unregister(&balloon_sysdev_class);
 553                 return error;
 554         }
 555
 556         for (i = 0; i < ARRAY_SIZE(balloon_attrs); i++) {
 557                 error = sysdev_create_file(sysdev, balloon_attrs[i]);
 558                 if (error)
 559                         goto fail;
 560         }
 561
 562         error = sysfs_create_group(&sysdev->kobj, &balloon_info_group);
 563         if (error)
 564                 goto fail;
 565
 566         return 0;
 567
 568  fail:
 569         while (--i >= 0)
 570                 sysdev_remove_file(sysdev, balloon_attrs[i]);
 571         sysdev_unregister(sysdev);
 572         sysdev_class_unregister(&balloon_sysdev_class);
 573         return error;
 574 }
 575
 576 MODULE_LICENSE("GPL");