1 /* 2 * Virtio balloon implementation, inspired by Dor Laor and Marcelo 3 * Tosatti's implementations. 4 * 5 * Copyright 2008 Rusty Russell IBM Corporation 6 * 7 * This program is free software; you can redistribute it and/or modify 8 * it under the terms of the GNU General Public License as published by 9 * the Free Software Foundation; either version 2 of the License, or 10 * (at your option) any later version. 11 * 12 * This program is distributed in the hope that it will be useful, 13 * but WITHOUT ANY WARRANTY; without even the implied warranty of 14 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the 15 * GNU General Public License for more details. 16 * 17 * You should have received a copy of the GNU General Public License 18 * along with this program; if not, write to the Free Software 19 * Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA 20 */ 21 22 #include <linux/virtio.h> 23 #include <linux/virtio_balloon.h> 24 #include <linux/swap.h> 25 #include <linux/kthread.h> 26 #include <linux/freezer.h> 27 #include <linux/delay.h> 28 #include <linux/slab.h> 29 #include <linux/module.h> 30 #include <linux/balloon_compaction.h> 31 #include <linux/oom.h> 32 #include <linux/wait.h> 33 34 /* 35 * Balloon device works in 4K page units. So each page is pointed to by 36 * multiple balloon pages. All memory counters in this driver are in balloon 37 * page units. 38 */ 39 #define VIRTIO_BALLOON_PAGES_PER_PAGE (unsigned)(PAGE_SIZE >> VIRTIO_BALLOON_PFN_SHIFT) 40 #define VIRTIO_BALLOON_ARRAY_PFNS_MAX 256 41 #define OOM_VBALLOON_DEFAULT_PAGES 256 42 #define VIRTBALLOON_OOM_NOTIFY_PRIORITY 80 43 44 static int oom_pages = OOM_VBALLOON_DEFAULT_PAGES; 45 module_param(oom_pages, int, S_IRUSR | S_IWUSR); 46 MODULE_PARM_DESC(oom_pages, "pages to free on OOM"); 47 48 struct virtio_balloon { 49 struct virtio_device *vdev; 50 struct virtqueue *inflate_vq, *deflate_vq, *stats_vq; 51 52 /* Where the ballooning thread waits for config to change. */ 53 wait_queue_head_t config_change; 54 55 /* The thread servicing the balloon. */ 56 struct task_struct *thread; 57 58 /* Waiting for host to ack the pages we released. */ 59 wait_queue_head_t acked; 60 61 /* Number of balloon pages we've told the Host we're not using. */ 62 unsigned int num_pages; 63 /* 64 * The pages we've told the Host we're not using are enqueued 65 * at vb_dev_info->pages list. 66 * Each page on this list adds VIRTIO_BALLOON_PAGES_PER_PAGE 67 * to num_pages above. 68 */ 69 struct balloon_dev_info vb_dev_info; 70 71 /* Synchronize access/update to this struct virtio_balloon elements */ 72 struct mutex balloon_lock; 73 74 /* The array of pfns we tell the Host about. */ 75 unsigned int num_pfns; 76 u32 pfns[VIRTIO_BALLOON_ARRAY_PFNS_MAX]; 77 78 /* Memory statistics */ 79 int need_stats_update; 80 struct virtio_balloon_stat stats[VIRTIO_BALLOON_S_NR]; 81 82 /* To register callback in oom notifier call chain */ 83 struct notifier_block nb; 84 }; 85 86 static struct virtio_device_id id_table[] = { 87 { VIRTIO_ID_BALLOON, VIRTIO_DEV_ANY_ID }, 88 { 0 }, 89 }; 90 91 static u32 page_to_balloon_pfn(struct page *page) 92 { 93 unsigned long pfn = page_to_pfn(page); 94 95 BUILD_BUG_ON(PAGE_SHIFT < VIRTIO_BALLOON_PFN_SHIFT); 96 /* Convert pfn from Linux page size to balloon page size. */ 97 return pfn * VIRTIO_BALLOON_PAGES_PER_PAGE; 98 } 99 100 static struct page *balloon_pfn_to_page(u32 pfn) 101 { 102 BUG_ON(pfn % VIRTIO_BALLOON_PAGES_PER_PAGE); 103 return pfn_to_page(pfn / VIRTIO_BALLOON_PAGES_PER_PAGE); 104 } 105 106 static void balloon_ack(struct virtqueue *vq) 107 { 108 struct virtio_balloon *vb = vq->vdev->priv; 109 110 wake_up(&vb->acked); 111 } 112 113 static void tell_host(struct virtio_balloon *vb, struct virtqueue *vq) 114 { 115 struct scatterlist sg; 116 unsigned int len; 117 118 sg_init_one(&sg, vb->pfns, sizeof(vb->pfns[0]) * vb->num_pfns); 119 120 /* We should always be able to add one buffer to an empty queue. */ 121 virtqueue_add_outbuf(vq, &sg, 1, vb, GFP_KERNEL); 122 virtqueue_kick(vq); 123 124 /* When host has read buffer, this completes via balloon_ack */ 125 wait_event(vb->acked, virtqueue_get_buf(vq, &len)); 126 } 127 128 static void set_page_pfns(u32 pfns[], struct page *page) 129 { 130 unsigned int i; 131 132 /* Set balloon pfns pointing at this page. 133 * Note that the first pfn points at start of the page. */ 134 for (i = 0; i < VIRTIO_BALLOON_PAGES_PER_PAGE; i++) 135 pfns[i] = page_to_balloon_pfn(page) + i; 136 } 137 138 static void fill_balloon(struct virtio_balloon *vb, size_t num) 139 { 140 struct balloon_dev_info *vb_dev_info = &vb->vb_dev_info; 141 142 /* We can only do one array worth at a time. */ 143 num = min(num, ARRAY_SIZE(vb->pfns)); 144 145 mutex_lock(&vb->balloon_lock); 146 for (vb->num_pfns = 0; vb->num_pfns < num; 147 vb->num_pfns += VIRTIO_BALLOON_PAGES_PER_PAGE) { 148 struct page *page = balloon_page_enqueue(vb_dev_info); 149 150 if (!page) { 151 dev_info_ratelimited(&vb->vdev->dev, 152 "Out of puff! Can't get %u pages\n", 153 VIRTIO_BALLOON_PAGES_PER_PAGE); 154 /* Sleep for at least 1/5 of a second before retry. */ 155 msleep(200); 156 break; 157 } 158 set_page_pfns(vb->pfns + vb->num_pfns, page); 159 vb->num_pages += VIRTIO_BALLOON_PAGES_PER_PAGE; 160 adjust_managed_page_count(page, -1); 161 } 162 163 /* Did we get any? */ 164 if (vb->num_pfns != 0) 165 tell_host(vb, vb->inflate_vq); 166 mutex_unlock(&vb->balloon_lock); 167 } 168 169 static void release_pages_by_pfn(const u32 pfns[], unsigned int num) 170 { 171 unsigned int i; 172 173 /* Find pfns pointing at start of each page, get pages and free them. */ 174 for (i = 0; i < num; i += VIRTIO_BALLOON_PAGES_PER_PAGE) { 175 struct page *page = balloon_pfn_to_page(pfns[i]); 176 adjust_managed_page_count(page, 1); 177 put_page(page); /* balloon reference */ 178 } 179 } 180 181 static unsigned leak_balloon(struct virtio_balloon *vb, size_t num) 182 { 183 unsigned num_freed_pages; 184 struct page *page; 185 struct balloon_dev_info *vb_dev_info = &vb->vb_dev_info; 186 187 /* We can only do one array worth at a time. */ 188 num = min(num, ARRAY_SIZE(vb->pfns)); 189 190 mutex_lock(&vb->balloon_lock); 191 for (vb->num_pfns = 0; vb->num_pfns < num; 192 vb->num_pfns += VIRTIO_BALLOON_PAGES_PER_PAGE) { 193 page = balloon_page_dequeue(vb_dev_info); 194 if (!page) 195 break; 196 set_page_pfns(vb->pfns + vb->num_pfns, page); 197 vb->num_pages -= VIRTIO_BALLOON_PAGES_PER_PAGE; 198 } 199 200 num_freed_pages = vb->num_pfns; 201 /* 202 * Note that if 203 * virtio_has_feature(vdev, VIRTIO_BALLOON_F_MUST_TELL_HOST); 204 * is true, we *have* to do it in this order 205 */ 206 if (vb->num_pfns != 0) 207 tell_host(vb, vb->deflate_vq); 208 mutex_unlock(&vb->balloon_lock); 209 release_pages_by_pfn(vb->pfns, vb->num_pfns); 210 return num_freed_pages; 211 } 212 213 static inline void update_stat(struct virtio_balloon *vb, int idx, 214 u16 tag, u64 val) 215 { 216 BUG_ON(idx >= VIRTIO_BALLOON_S_NR); 217 vb->stats[idx].tag = tag; 218 vb->stats[idx].val = val; 219 } 220 221 #define pages_to_bytes(x) ((u64)(x) << PAGE_SHIFT) 222 223 static void update_balloon_stats(struct virtio_balloon *vb) 224 { 225 unsigned long events[NR_VM_EVENT_ITEMS]; 226 struct sysinfo i; 227 int idx = 0; 228 229 all_vm_events(events); 230 si_meminfo(&i); 231 232 update_stat(vb, idx++, VIRTIO_BALLOON_S_SWAP_IN, 233 pages_to_bytes(events[PSWPIN])); 234 update_stat(vb, idx++, VIRTIO_BALLOON_S_SWAP_OUT, 235 pages_to_bytes(events[PSWPOUT])); 236 update_stat(vb, idx++, VIRTIO_BALLOON_S_MAJFLT, events[PGMAJFAULT]); 237 update_stat(vb, idx++, VIRTIO_BALLOON_S_MINFLT, events[PGFAULT]); 238 update_stat(vb, idx++, VIRTIO_BALLOON_S_MEMFREE, 239 pages_to_bytes(i.freeram)); 240 update_stat(vb, idx++, VIRTIO_BALLOON_S_MEMTOT, 241 pages_to_bytes(i.totalram)); 242 } 243 244 /* 245 * While most virtqueues communicate guest-initiated requests to the hypervisor, 246 * the stats queue operates in reverse. The driver initializes the virtqueue 247 * with a single buffer. From that point forward, all conversations consist of 248 * a hypervisor request (a call to this function) which directs us to refill 249 * the virtqueue with a fresh stats buffer. Since stats collection can sleep, 250 * we notify our kthread which does the actual work via stats_handle_request(). 251 */ 252 static void stats_request(struct virtqueue *vq) 253 { 254 struct virtio_balloon *vb = vq->vdev->priv; 255 256 vb->need_stats_update = 1; 257 wake_up(&vb->config_change); 258 } 259 260 static void stats_handle_request(struct virtio_balloon *vb) 261 { 262 struct virtqueue *vq; 263 struct scatterlist sg; 264 unsigned int len; 265 266 vb->need_stats_update = 0; 267 update_balloon_stats(vb); 268 269 vq = vb->stats_vq; 270 if (!virtqueue_get_buf(vq, &len)) 271 return; 272 sg_init_one(&sg, vb->stats, sizeof(vb->stats)); 273 virtqueue_add_outbuf(vq, &sg, 1, vb, GFP_KERNEL); 274 virtqueue_kick(vq); 275 } 276 277 static void virtballoon_changed(struct virtio_device *vdev) 278 { 279 struct virtio_balloon *vb = vdev->priv; 280 281 wake_up(&vb->config_change); 282 } 283 284 static inline s64 towards_target(struct virtio_balloon *vb) 285 { 286 __le32 v; 287 s64 target; 288 289 virtio_cread(vb->vdev, struct virtio_balloon_config, num_pages, &v); 290 291 target = le32_to_cpu(v); 292 return target - vb->num_pages; 293 } 294 295 static void update_balloon_size(struct virtio_balloon *vb) 296 { 297 __le32 actual = cpu_to_le32(vb->num_pages); 298 299 virtio_cwrite(vb->vdev, struct virtio_balloon_config, actual, 300 &actual); 301 } 302 303 /* 304 * virtballoon_oom_notify - release pages when system is under severe 305 * memory pressure (called from out_of_memory()) 306 * @self : notifier block struct 307 * @dummy: not used 308 * @parm : returned - number of freed pages 309 * 310 * The balancing of memory by use of the virtio balloon should not cause 311 * the termination of processes while there are pages in the balloon. 312 * If virtio balloon manages to release some memory, it will make the 313 * system return and retry the allocation that forced the OOM killer 314 * to run. 315 */ 316 static int virtballoon_oom_notify(struct notifier_block *self, 317 unsigned long dummy, void *parm) 318 { 319 struct virtio_balloon *vb; 320 unsigned long *freed; 321 unsigned num_freed_pages; 322 323 vb = container_of(self, struct virtio_balloon, nb); 324 if (!virtio_has_feature(vb->vdev, VIRTIO_BALLOON_F_DEFLATE_ON_OOM)) 325 return NOTIFY_OK; 326 327 freed = parm; 328 num_freed_pages = leak_balloon(vb, oom_pages); 329 update_balloon_size(vb); 330 *freed += num_freed_pages; 331 332 return NOTIFY_OK; 333 } 334 335 static int balloon(void *_vballoon) 336 { 337 struct virtio_balloon *vb = _vballoon; 338 DEFINE_WAIT_FUNC(wait, woken_wake_function); 339 340 set_freezable(); 341 while (!kthread_should_stop()) { 342 s64 diff; 343 344 try_to_freeze(); 345 346 add_wait_queue(&vb->config_change, &wait); 347 for (;;) { 348 if ((diff = towards_target(vb)) != 0 || 349 vb->need_stats_update || 350 kthread_should_stop() || 351 freezing(current)) 352 break; 353 wait_woken(&wait, TASK_INTERRUPTIBLE, MAX_SCHEDULE_TIMEOUT); 354 } 355 remove_wait_queue(&vb->config_change, &wait); 356 357 if (vb->need_stats_update) 358 stats_handle_request(vb); 359 if (diff > 0) 360 fill_balloon(vb, diff); 361 else if (diff < 0) 362 leak_balloon(vb, -diff); 363 update_balloon_size(vb); 364 365 /* 366 * For large balloon changes, we could spend a lot of time 367 * and always have work to do. Be nice if preempt disabled. 368 */ 369 cond_resched(); 370 } 371 return 0; 372 } 373 374 static int init_vqs(struct virtio_balloon *vb) 375 { 376 struct virtqueue *vqs[3]; 377 vq_callback_t *callbacks[] = { balloon_ack, balloon_ack, stats_request }; 378 const char *names[] = { "inflate", "deflate", "stats" }; 379 int err, nvqs; 380 381 /* 382 * We expect two virtqueues: inflate and deflate, and 383 * optionally stat. 384 */ 385 nvqs = virtio_has_feature(vb->vdev, VIRTIO_BALLOON_F_STATS_VQ) ? 3 : 2; 386 err = vb->vdev->config->find_vqs(vb->vdev, nvqs, vqs, callbacks, names); 387 if (err) 388 return err; 389 390 vb->inflate_vq = vqs[0]; 391 vb->deflate_vq = vqs[1]; 392 if (virtio_has_feature(vb->vdev, VIRTIO_BALLOON_F_STATS_VQ)) { 393 struct scatterlist sg; 394 vb->stats_vq = vqs[2]; 395 396 /* 397 * Prime this virtqueue with one buffer so the hypervisor can 398 * use it to signal us later (it can't be broken yet!). 399 */ 400 sg_init_one(&sg, vb->stats, sizeof vb->stats); 401 if (virtqueue_add_outbuf(vb->stats_vq, &sg, 1, vb, GFP_KERNEL) 402 < 0) 403 BUG(); 404 virtqueue_kick(vb->stats_vq); 405 } 406 return 0; 407 } 408 409 #ifdef CONFIG_BALLOON_COMPACTION 410 /* 411 * virtballoon_migratepage - perform the balloon page migration on behalf of 412 * a compation thread. (called under page lock) 413 * @vb_dev_info: the balloon device 414 * @newpage: page that will replace the isolated page after migration finishes. 415 * @page : the isolated (old) page that is about to be migrated to newpage. 416 * @mode : compaction mode -- not used for balloon page migration. 417 * 418 * After a ballooned page gets isolated by compaction procedures, this is the 419 * function that performs the page migration on behalf of a compaction thread 420 * The page migration for virtio balloon is done in a simple swap fashion which 421 * follows these two macro steps: 422 * 1) insert newpage into vb->pages list and update the host about it; 423 * 2) update the host about the old page removed from vb->pages list; 424 * 425 * This function preforms the balloon page migration task. 426 * Called through balloon_mapping->a_ops->migratepage 427 */ 428 static int virtballoon_migratepage(struct balloon_dev_info *vb_dev_info, 429 struct page *newpage, struct page *page, enum migrate_mode mode) 430 { 431 struct virtio_balloon *vb = container_of(vb_dev_info, 432 struct virtio_balloon, vb_dev_info); 433 unsigned long flags; 434 435 /* 436 * In order to avoid lock contention while migrating pages concurrently 437 * to leak_balloon() or fill_balloon() we just give up the balloon_lock 438 * this turn, as it is easier to retry the page migration later. 439 * This also prevents fill_balloon() getting stuck into a mutex 440 * recursion in the case it ends up triggering memory compaction 441 * while it is attempting to inflate the ballon. 442 */ 443 if (!mutex_trylock(&vb->balloon_lock)) 444 return -EAGAIN; 445 446 get_page(newpage); /* balloon reference */ 447 448 /* balloon's page migration 1st step -- inflate "newpage" */ 449 spin_lock_irqsave(&vb_dev_info->pages_lock, flags); 450 balloon_page_insert(vb_dev_info, newpage); 451 vb_dev_info->isolated_pages--; 452 __count_vm_event(BALLOON_MIGRATE); 453 spin_unlock_irqrestore(&vb_dev_info->pages_lock, flags); 454 vb->num_pfns = VIRTIO_BALLOON_PAGES_PER_PAGE; 455 set_page_pfns(vb->pfns, newpage); 456 tell_host(vb, vb->inflate_vq); 457 458 /* balloon's page migration 2nd step -- deflate "page" */ 459 balloon_page_delete(page); 460 vb->num_pfns = VIRTIO_BALLOON_PAGES_PER_PAGE; 461 set_page_pfns(vb->pfns, page); 462 tell_host(vb, vb->deflate_vq); 463 464 mutex_unlock(&vb->balloon_lock); 465 466 put_page(page); /* balloon reference */ 467 468 return MIGRATEPAGE_SUCCESS; 469 } 470 #endif /* CONFIG_BALLOON_COMPACTION */ 471 472 static int virtballoon_probe(struct virtio_device *vdev) 473 { 474 struct virtio_balloon *vb; 475 int err; 476 477 if (!vdev->config->get) { 478 dev_err(&vdev->dev, "%s failure: config access disabled\n", 479 __func__); 480 return -EINVAL; 481 } 482 483 vdev->priv = vb = kmalloc(sizeof(*vb), GFP_KERNEL); 484 if (!vb) { 485 err = -ENOMEM; 486 goto out; 487 } 488 489 vb->num_pages = 0; 490 mutex_init(&vb->balloon_lock); 491 init_waitqueue_head(&vb->config_change); 492 init_waitqueue_head(&vb->acked); 493 vb->vdev = vdev; 494 vb->need_stats_update = 0; 495 496 balloon_devinfo_init(&vb->vb_dev_info); 497 #ifdef CONFIG_BALLOON_COMPACTION 498 vb->vb_dev_info.migratepage = virtballoon_migratepage; 499 #endif 500 501 err = init_vqs(vb); 502 if (err) 503 goto out_free_vb; 504 505 vb->nb.notifier_call = virtballoon_oom_notify; 506 vb->nb.priority = VIRTBALLOON_OOM_NOTIFY_PRIORITY; 507 err = register_oom_notifier(&vb->nb); 508 if (err < 0) 509 goto out_oom_notify; 510 511 virtio_device_ready(vdev); 512 513 vb->thread = kthread_run(balloon, vb, "vballoon"); 514 if (IS_ERR(vb->thread)) { 515 err = PTR_ERR(vb->thread); 516 goto out_del_vqs; 517 } 518 519 return 0; 520 521 out_del_vqs: 522 unregister_oom_notifier(&vb->nb); 523 out_oom_notify: 524 vdev->config->del_vqs(vdev); 525 out_free_vb: 526 kfree(vb); 527 out: 528 return err; 529 } 530 531 static void remove_common(struct virtio_balloon *vb) 532 { 533 /* There might be pages left in the balloon: free them. */ 534 while (vb->num_pages) 535 leak_balloon(vb, vb->num_pages); 536 update_balloon_size(vb); 537 538 /* Now we reset the device so we can clean up the queues. */ 539 vb->vdev->config->reset(vb->vdev); 540 541 vb->vdev->config->del_vqs(vb->vdev); 542 } 543 544 static void virtballoon_remove(struct virtio_device *vdev) 545 { 546 struct virtio_balloon *vb = vdev->priv; 547 548 unregister_oom_notifier(&vb->nb); 549 kthread_stop(vb->thread); 550 remove_common(vb); 551 kfree(vb); 552 } 553 554 #ifdef CONFIG_PM_SLEEP 555 static int virtballoon_freeze(struct virtio_device *vdev) 556 { 557 struct virtio_balloon *vb = vdev->priv; 558 559 /* 560 * The kthread is already frozen by the PM core before this 561 * function is called. 562 */ 563 564 remove_common(vb); 565 return 0; 566 } 567 568 static int virtballoon_restore(struct virtio_device *vdev) 569 { 570 struct virtio_balloon *vb = vdev->priv; 571 int ret; 572 573 ret = init_vqs(vdev->priv); 574 if (ret) 575 return ret; 576 577 virtio_device_ready(vdev); 578 579 fill_balloon(vb, towards_target(vb)); 580 update_balloon_size(vb); 581 return 0; 582 } 583 #endif 584 585 static unsigned int features[] = { 586 VIRTIO_BALLOON_F_MUST_TELL_HOST, 587 VIRTIO_BALLOON_F_STATS_VQ, 588 VIRTIO_BALLOON_F_DEFLATE_ON_OOM, 589 }; 590 591 static struct virtio_driver virtio_balloon_driver = { 592 .feature_table = features, 593 .feature_table_size = ARRAY_SIZE(features), 594 .driver.name = KBUILD_MODNAME, 595 .driver.owner = THIS_MODULE, 596 .id_table = id_table, 597 .probe = virtballoon_probe, 598 .remove = virtballoon_remove, 599 .config_changed = virtballoon_changed, 600 #ifdef CONFIG_PM_SLEEP 601 .freeze = virtballoon_freeze, 602 .restore = virtballoon_restore, 603 #endif 604 }; 605 606 module_virtio_driver(virtio_balloon_driver); 607 MODULE_DEVICE_TABLE(virtio, id_table); 608 MODULE_DESCRIPTION("Virtio balloon driver"); 609 MODULE_LICENSE("GPL"); 610