1 // SPDX-License-Identifier: GPL-2.0-or-later 2 /* 3 * Virtio balloon implementation, inspired by Dor Laor and Marcelo 4 * Tosatti's implementations. 5 * 6 * Copyright 2008 Rusty Russell IBM Corporation 7 */ 8 9 #include <linux/virtio.h> 10 #include <linux/virtio_balloon.h> 11 #include <linux/swap.h> 12 #include <linux/workqueue.h> 13 #include <linux/delay.h> 14 #include <linux/slab.h> 15 #include <linux/module.h> 16 #include <linux/balloon_compaction.h> 17 #include <linux/oom.h> 18 #include <linux/wait.h> 19 #include <linux/mm.h> 20 #include <linux/page_reporting.h> 21 22 /* 23 * Balloon device works in 4K page units. So each page is pointed to by 24 * multiple balloon pages. All memory counters in this driver are in balloon 25 * page units. 26 */ 27 #define VIRTIO_BALLOON_PAGES_PER_PAGE (unsigned int)(PAGE_SIZE >> VIRTIO_BALLOON_PFN_SHIFT) 28 #define VIRTIO_BALLOON_ARRAY_PFNS_MAX 256 29 /* Maximum number of (4k) pages to deflate on OOM notifications. */ 30 #define VIRTIO_BALLOON_OOM_NR_PAGES 256 31 #define VIRTIO_BALLOON_OOM_NOTIFY_PRIORITY 80 32 33 #define VIRTIO_BALLOON_FREE_PAGE_ALLOC_FLAG (__GFP_NORETRY | __GFP_NOWARN | \ 34 __GFP_NOMEMALLOC) 35 /* The order of free page blocks to report to host */ 36 #define VIRTIO_BALLOON_HINT_BLOCK_ORDER MAX_PAGE_ORDER 37 /* The size of a free page block in bytes */ 38 #define VIRTIO_BALLOON_HINT_BLOCK_BYTES \ 39 (1 << (VIRTIO_BALLOON_HINT_BLOCK_ORDER + PAGE_SHIFT)) 40 #define VIRTIO_BALLOON_HINT_BLOCK_PAGES (1 << VIRTIO_BALLOON_HINT_BLOCK_ORDER) 41 42 enum virtio_balloon_vq { 43 VIRTIO_BALLOON_VQ_INFLATE, 44 VIRTIO_BALLOON_VQ_DEFLATE, 45 VIRTIO_BALLOON_VQ_STATS, 46 VIRTIO_BALLOON_VQ_FREE_PAGE, 47 VIRTIO_BALLOON_VQ_REPORTING, 48 VIRTIO_BALLOON_VQ_MAX 49 }; 50 51 enum virtio_balloon_config_read { 52 VIRTIO_BALLOON_CONFIG_READ_CMD_ID = 0, 53 }; 54 55 struct virtio_balloon { 56 struct virtio_device *vdev; 57 struct virtqueue *inflate_vq, *deflate_vq, *stats_vq, *free_page_vq; 58 59 /* Balloon's own wq for cpu-intensive work items */ 60 struct workqueue_struct *balloon_wq; 61 /* The free page reporting work item submitted to the balloon wq */ 62 struct work_struct report_free_page_work; 63 64 /* The balloon servicing is delegated to a freezable workqueue. */ 65 struct work_struct update_balloon_stats_work; 66 struct work_struct update_balloon_size_work; 67 68 /* Prevent updating balloon when it is being canceled. */ 69 spinlock_t stop_update_lock; 70 bool stop_update; 71 /* Bitmap to indicate if reading the related config fields are needed */ 72 unsigned long config_read_bitmap; 73 74 /* The list of allocated free pages, waiting to be given back to mm */ 75 struct list_head free_page_list; 76 spinlock_t free_page_list_lock; 77 /* The number of free page blocks on the above list */ 78 unsigned long num_free_page_blocks; 79 /* 80 * The cmd id received from host. 81 * Read it via virtio_balloon_cmd_id_received to get the latest value 82 * sent from host. 83 */ 84 u32 cmd_id_received_cache; 85 /* The cmd id that is actively in use */ 86 __virtio32 cmd_id_active; 87 /* Buffer to store the stop sign */ 88 __virtio32 cmd_id_stop; 89 90 /* Waiting for host to ack the pages we released. */ 91 wait_queue_head_t acked; 92 93 /* Number of balloon pages we've told the Host we're not using. */ 94 unsigned int num_pages; 95 /* 96 * The pages we've told the Host we're not using are enqueued 97 * at vb_dev_info->pages list. 98 * Each page on this list adds VIRTIO_BALLOON_PAGES_PER_PAGE 99 * to num_pages above. 100 */ 101 struct balloon_dev_info vb_dev_info; 102 103 /* Synchronize access/update to this struct virtio_balloon elements */ 104 struct mutex balloon_lock; 105 106 /* The array of pfns we tell the Host about. */ 107 unsigned int num_pfns; 108 __virtio32 pfns[VIRTIO_BALLOON_ARRAY_PFNS_MAX]; 109 110 /* Memory statistics */ 111 struct virtio_balloon_stat stats[VIRTIO_BALLOON_S_NR]; 112 113 /* Shrinker to return free pages - VIRTIO_BALLOON_F_FREE_PAGE_HINT */ 114 struct shrinker *shrinker; 115 116 /* OOM notifier to deflate on OOM - VIRTIO_BALLOON_F_DEFLATE_ON_OOM */ 117 struct notifier_block oom_nb; 118 119 /* Free page reporting device */ 120 struct virtqueue *reporting_vq; 121 struct page_reporting_dev_info pr_dev_info; 122 123 /* State for keeping the wakeup_source active while adjusting the balloon */ 124 spinlock_t wakeup_lock; 125 bool processing_wakeup_event; 126 u32 wakeup_signal_mask; 127 }; 128 129 #define VIRTIO_BALLOON_WAKEUP_SIGNAL_ADJUST (1 << 0) 130 #define VIRTIO_BALLOON_WAKEUP_SIGNAL_STATS (1 << 1) 131 132 static const struct virtio_device_id id_table[] = { 133 { VIRTIO_ID_BALLOON, VIRTIO_DEV_ANY_ID }, 134 { 0 }, 135 }; 136 137 static u32 page_to_balloon_pfn(struct page *page) 138 { 139 unsigned long pfn = page_to_pfn(page); 140 141 BUILD_BUG_ON(PAGE_SHIFT < VIRTIO_BALLOON_PFN_SHIFT); 142 /* Convert pfn from Linux page size to balloon page size. */ 143 return pfn * VIRTIO_BALLOON_PAGES_PER_PAGE; 144 } 145 146 static void start_wakeup_event(struct virtio_balloon *vb, u32 mask) 147 { 148 unsigned long flags; 149 150 spin_lock_irqsave(&vb->wakeup_lock, flags); 151 vb->wakeup_signal_mask |= mask; 152 if (!vb->processing_wakeup_event) { 153 vb->processing_wakeup_event = true; 154 pm_stay_awake(&vb->vdev->dev); 155 } 156 spin_unlock_irqrestore(&vb->wakeup_lock, flags); 157 } 158 159 static void process_wakeup_event(struct virtio_balloon *vb, u32 mask) 160 { 161 spin_lock_irq(&vb->wakeup_lock); 162 vb->wakeup_signal_mask &= ~mask; 163 spin_unlock_irq(&vb->wakeup_lock); 164 } 165 166 static void finish_wakeup_event(struct virtio_balloon *vb) 167 { 168 spin_lock_irq(&vb->wakeup_lock); 169 if (!vb->wakeup_signal_mask && vb->processing_wakeup_event) { 170 vb->processing_wakeup_event = false; 171 pm_relax(&vb->vdev->dev); 172 } 173 spin_unlock_irq(&vb->wakeup_lock); 174 } 175 176 static void balloon_ack(struct virtqueue *vq) 177 { 178 struct virtio_balloon *vb = vq->vdev->priv; 179 180 wake_up(&vb->acked); 181 } 182 183 static void tell_host(struct virtio_balloon *vb, struct virtqueue *vq) 184 { 185 struct scatterlist sg; 186 unsigned int len; 187 188 sg_init_one(&sg, vb->pfns, sizeof(vb->pfns[0]) * vb->num_pfns); 189 190 /* We should always be able to add one buffer to an empty queue. */ 191 virtqueue_add_outbuf(vq, &sg, 1, vb, GFP_KERNEL); 192 virtqueue_kick(vq); 193 194 /* When host has read buffer, this completes via balloon_ack */ 195 wait_event(vb->acked, virtqueue_get_buf(vq, &len)); 196 197 } 198 199 static int virtballoon_free_page_report(struct page_reporting_dev_info *pr_dev_info, 200 struct scatterlist *sg, unsigned int nents) 201 { 202 struct virtio_balloon *vb = 203 container_of(pr_dev_info, struct virtio_balloon, pr_dev_info); 204 struct virtqueue *vq = vb->reporting_vq; 205 unsigned int unused, err; 206 207 /* We should always be able to add these buffers to an empty queue. */ 208 err = virtqueue_add_inbuf(vq, sg, nents, vb, GFP_NOWAIT | __GFP_NOWARN); 209 210 /* 211 * In the extremely unlikely case that something has occurred and we 212 * are able to trigger an error we will simply display a warning 213 * and exit without actually processing the pages. 214 */ 215 if (WARN_ON_ONCE(err)) 216 return err; 217 218 virtqueue_kick(vq); 219 220 /* When host has read buffer, this completes via balloon_ack */ 221 wait_event(vb->acked, virtqueue_get_buf(vq, &unused)); 222 223 return 0; 224 } 225 226 static void set_page_pfns(struct virtio_balloon *vb, 227 __virtio32 pfns[], struct page *page) 228 { 229 unsigned int i; 230 231 BUILD_BUG_ON(VIRTIO_BALLOON_PAGES_PER_PAGE > VIRTIO_BALLOON_ARRAY_PFNS_MAX); 232 233 /* 234 * Set balloon pfns pointing at this page. 235 * Note that the first pfn points at start of the page. 236 */ 237 for (i = 0; i < VIRTIO_BALLOON_PAGES_PER_PAGE; i++) 238 pfns[i] = cpu_to_virtio32(vb->vdev, 239 page_to_balloon_pfn(page) + i); 240 } 241 242 static unsigned int fill_balloon(struct virtio_balloon *vb, size_t num) 243 { 244 unsigned int num_allocated_pages; 245 unsigned int num_pfns; 246 struct page *page; 247 LIST_HEAD(pages); 248 249 /* We can only do one array worth at a time. */ 250 num = min(num, ARRAY_SIZE(vb->pfns)); 251 252 for (num_pfns = 0; num_pfns < num; 253 num_pfns += VIRTIO_BALLOON_PAGES_PER_PAGE) { 254 struct page *page = balloon_page_alloc(); 255 256 if (!page) { 257 dev_info_ratelimited(&vb->vdev->dev, 258 "Out of puff! Can't get %u pages\n", 259 VIRTIO_BALLOON_PAGES_PER_PAGE); 260 /* Sleep for at least 1/5 of a second before retry. */ 261 msleep(200); 262 break; 263 } 264 265 balloon_page_push(&pages, page); 266 } 267 268 mutex_lock(&vb->balloon_lock); 269 270 vb->num_pfns = 0; 271 272 while ((page = balloon_page_pop(&pages))) { 273 balloon_page_enqueue(&vb->vb_dev_info, page); 274 275 set_page_pfns(vb, vb->pfns + vb->num_pfns, page); 276 vb->num_pages += VIRTIO_BALLOON_PAGES_PER_PAGE; 277 if (!virtio_has_feature(vb->vdev, 278 VIRTIO_BALLOON_F_DEFLATE_ON_OOM)) 279 adjust_managed_page_count(page, -1); 280 vb->num_pfns += VIRTIO_BALLOON_PAGES_PER_PAGE; 281 } 282 283 num_allocated_pages = vb->num_pfns; 284 /* Did we get any? */ 285 if (vb->num_pfns != 0) 286 tell_host(vb, vb->inflate_vq); 287 mutex_unlock(&vb->balloon_lock); 288 289 return num_allocated_pages; 290 } 291 292 static void release_pages_balloon(struct virtio_balloon *vb, 293 struct list_head *pages) 294 { 295 struct page *page, *next; 296 297 list_for_each_entry_safe(page, next, pages, lru) { 298 if (!virtio_has_feature(vb->vdev, 299 VIRTIO_BALLOON_F_DEFLATE_ON_OOM)) 300 adjust_managed_page_count(page, 1); 301 list_del(&page->lru); 302 put_page(page); /* balloon reference */ 303 } 304 } 305 306 static unsigned int leak_balloon(struct virtio_balloon *vb, size_t num) 307 { 308 unsigned int num_freed_pages; 309 struct page *page; 310 struct balloon_dev_info *vb_dev_info = &vb->vb_dev_info; 311 LIST_HEAD(pages); 312 313 /* We can only do one array worth at a time. */ 314 num = min(num, ARRAY_SIZE(vb->pfns)); 315 316 mutex_lock(&vb->balloon_lock); 317 /* We can't release more pages than taken */ 318 num = min(num, (size_t)vb->num_pages); 319 for (vb->num_pfns = 0; vb->num_pfns < num; 320 vb->num_pfns += VIRTIO_BALLOON_PAGES_PER_PAGE) { 321 page = balloon_page_dequeue(vb_dev_info); 322 if (!page) 323 break; 324 set_page_pfns(vb, vb->pfns + vb->num_pfns, page); 325 list_add(&page->lru, &pages); 326 vb->num_pages -= VIRTIO_BALLOON_PAGES_PER_PAGE; 327 } 328 329 num_freed_pages = vb->num_pfns; 330 /* 331 * Note that if 332 * virtio_has_feature(vdev, VIRTIO_BALLOON_F_MUST_TELL_HOST); 333 * is true, we *have* to do it in this order 334 */ 335 if (vb->num_pfns != 0) 336 tell_host(vb, vb->deflate_vq); 337 release_pages_balloon(vb, &pages); 338 mutex_unlock(&vb->balloon_lock); 339 return num_freed_pages; 340 } 341 342 static inline void update_stat(struct virtio_balloon *vb, int idx, 343 u16 tag, u64 val) 344 { 345 BUG_ON(idx >= VIRTIO_BALLOON_S_NR); 346 vb->stats[idx].tag = cpu_to_virtio16(vb->vdev, tag); 347 vb->stats[idx].val = cpu_to_virtio64(vb->vdev, val); 348 } 349 350 #define pages_to_bytes(x) ((u64)(x) << PAGE_SHIFT) 351 352 #ifdef CONFIG_VM_EVENT_COUNTERS 353 /* Return the number of entries filled by vm events */ 354 static inline unsigned int update_balloon_vm_stats(struct virtio_balloon *vb) 355 { 356 unsigned long events[NR_VM_EVENT_ITEMS]; 357 unsigned int idx = 0; 358 359 all_vm_events(events); 360 update_stat(vb, idx++, VIRTIO_BALLOON_S_SWAP_IN, 361 pages_to_bytes(events[PSWPIN])); 362 update_stat(vb, idx++, VIRTIO_BALLOON_S_SWAP_OUT, 363 pages_to_bytes(events[PSWPOUT])); 364 update_stat(vb, idx++, VIRTIO_BALLOON_S_MAJFLT, events[PGMAJFAULT]); 365 update_stat(vb, idx++, VIRTIO_BALLOON_S_MINFLT, events[PGFAULT]); 366 update_stat(vb, idx++, VIRTIO_BALLOON_S_OOM_KILL, events[OOM_KILL]); 367 368 #ifdef CONFIG_HUGETLB_PAGE 369 update_stat(vb, idx++, VIRTIO_BALLOON_S_HTLB_PGALLOC, 370 events[HTLB_BUDDY_PGALLOC]); 371 update_stat(vb, idx++, VIRTIO_BALLOON_S_HTLB_PGFAIL, 372 events[HTLB_BUDDY_PGALLOC_FAIL]); 373 #endif /* CONFIG_HUGETLB_PAGE */ 374 375 return idx; 376 } 377 #else /* CONFIG_VM_EVENT_COUNTERS */ 378 static inline unsigned int update_balloon_vm_stats(struct virtio_balloon *vb) 379 { 380 return 0; 381 } 382 #endif /* CONFIG_VM_EVENT_COUNTERS */ 383 384 static unsigned int update_balloon_stats(struct virtio_balloon *vb) 385 { 386 struct sysinfo i; 387 unsigned int idx; 388 long available; 389 unsigned long caches; 390 391 idx = update_balloon_vm_stats(vb); 392 393 si_meminfo(&i); 394 available = si_mem_available(); 395 caches = global_node_page_state(NR_FILE_PAGES); 396 update_stat(vb, idx++, VIRTIO_BALLOON_S_MEMFREE, 397 pages_to_bytes(i.freeram)); 398 update_stat(vb, idx++, VIRTIO_BALLOON_S_MEMTOT, 399 pages_to_bytes(i.totalram)); 400 update_stat(vb, idx++, VIRTIO_BALLOON_S_AVAIL, 401 pages_to_bytes(available)); 402 update_stat(vb, idx++, VIRTIO_BALLOON_S_CACHES, 403 pages_to_bytes(caches)); 404 405 return idx; 406 } 407 408 /* 409 * While most virtqueues communicate guest-initiated requests to the hypervisor, 410 * the stats queue operates in reverse. The driver initializes the virtqueue 411 * with a single buffer. From that point forward, all conversations consist of 412 * a hypervisor request (a call to this function) which directs us to refill 413 * the virtqueue with a fresh stats buffer. Since stats collection can sleep, 414 * we delegate the job to a freezable workqueue that will do the actual work via 415 * stats_handle_request(). 416 */ 417 static void stats_request(struct virtqueue *vq) 418 { 419 struct virtio_balloon *vb = vq->vdev->priv; 420 421 spin_lock(&vb->stop_update_lock); 422 if (!vb->stop_update) { 423 start_wakeup_event(vb, VIRTIO_BALLOON_WAKEUP_SIGNAL_STATS); 424 queue_work(system_freezable_wq, &vb->update_balloon_stats_work); 425 } 426 spin_unlock(&vb->stop_update_lock); 427 } 428 429 static void stats_handle_request(struct virtio_balloon *vb) 430 { 431 struct virtqueue *vq; 432 struct scatterlist sg; 433 unsigned int len, num_stats; 434 435 num_stats = update_balloon_stats(vb); 436 437 vq = vb->stats_vq; 438 if (!virtqueue_get_buf(vq, &len)) 439 return; 440 sg_init_one(&sg, vb->stats, sizeof(vb->stats[0]) * num_stats); 441 virtqueue_add_outbuf(vq, &sg, 1, vb, GFP_KERNEL); 442 virtqueue_kick(vq); 443 } 444 445 static inline s64 towards_target(struct virtio_balloon *vb) 446 { 447 s64 target; 448 u32 num_pages; 449 450 /* Legacy balloon config space is LE, unlike all other devices. */ 451 virtio_cread_le(vb->vdev, struct virtio_balloon_config, num_pages, 452 &num_pages); 453 454 /* 455 * Aligned up to guest page size to avoid inflating and deflating 456 * balloon endlessly. 457 */ 458 target = ALIGN(num_pages, VIRTIO_BALLOON_PAGES_PER_PAGE); 459 return target - vb->num_pages; 460 } 461 462 /* Gives back @num_to_return blocks of free pages to mm. */ 463 static unsigned long return_free_pages_to_mm(struct virtio_balloon *vb, 464 unsigned long num_to_return) 465 { 466 struct page *page; 467 unsigned long num_returned; 468 469 spin_lock_irq(&vb->free_page_list_lock); 470 for (num_returned = 0; num_returned < num_to_return; num_returned++) { 471 page = balloon_page_pop(&vb->free_page_list); 472 if (!page) 473 break; 474 free_pages((unsigned long)page_address(page), 475 VIRTIO_BALLOON_HINT_BLOCK_ORDER); 476 } 477 vb->num_free_page_blocks -= num_returned; 478 spin_unlock_irq(&vb->free_page_list_lock); 479 480 return num_returned; 481 } 482 483 static void virtio_balloon_queue_free_page_work(struct virtio_balloon *vb) 484 { 485 if (!virtio_has_feature(vb->vdev, VIRTIO_BALLOON_F_FREE_PAGE_HINT)) 486 return; 487 488 /* No need to queue the work if the bit was already set. */ 489 if (test_and_set_bit(VIRTIO_BALLOON_CONFIG_READ_CMD_ID, 490 &vb->config_read_bitmap)) 491 return; 492 493 queue_work(vb->balloon_wq, &vb->report_free_page_work); 494 } 495 496 static void start_update_balloon_size(struct virtio_balloon *vb) 497 { 498 start_wakeup_event(vb, VIRTIO_BALLOON_WAKEUP_SIGNAL_ADJUST); 499 queue_work(system_freezable_wq, &vb->update_balloon_size_work); 500 } 501 502 static void virtballoon_changed(struct virtio_device *vdev) 503 { 504 struct virtio_balloon *vb = vdev->priv; 505 unsigned long flags; 506 507 spin_lock_irqsave(&vb->stop_update_lock, flags); 508 if (!vb->stop_update) { 509 start_update_balloon_size(vb); 510 virtio_balloon_queue_free_page_work(vb); 511 } 512 spin_unlock_irqrestore(&vb->stop_update_lock, flags); 513 } 514 515 static void update_balloon_size(struct virtio_balloon *vb) 516 { 517 u32 actual = vb->num_pages; 518 519 /* Legacy balloon config space is LE, unlike all other devices. */ 520 virtio_cwrite_le(vb->vdev, struct virtio_balloon_config, actual, 521 &actual); 522 } 523 524 static void update_balloon_stats_func(struct work_struct *work) 525 { 526 struct virtio_balloon *vb; 527 528 vb = container_of(work, struct virtio_balloon, 529 update_balloon_stats_work); 530 531 process_wakeup_event(vb, VIRTIO_BALLOON_WAKEUP_SIGNAL_STATS); 532 stats_handle_request(vb); 533 finish_wakeup_event(vb); 534 } 535 536 static void update_balloon_size_func(struct work_struct *work) 537 { 538 struct virtio_balloon *vb; 539 s64 diff; 540 541 vb = container_of(work, struct virtio_balloon, 542 update_balloon_size_work); 543 544 process_wakeup_event(vb, VIRTIO_BALLOON_WAKEUP_SIGNAL_ADJUST); 545 546 diff = towards_target(vb); 547 548 if (diff) { 549 if (diff > 0) 550 diff -= fill_balloon(vb, diff); 551 else 552 diff += leak_balloon(vb, -diff); 553 update_balloon_size(vb); 554 } 555 556 if (diff) 557 queue_work(system_freezable_wq, work); 558 else 559 finish_wakeup_event(vb); 560 } 561 562 static int init_vqs(struct virtio_balloon *vb) 563 { 564 struct virtqueue_info vqs_info[VIRTIO_BALLOON_VQ_MAX] = {}; 565 struct virtqueue *vqs[VIRTIO_BALLOON_VQ_MAX]; 566 int err; 567 568 /* 569 * Inflateq and deflateq are used unconditionally. The names[] 570 * will be NULL if the related feature is not enabled, which will 571 * cause no allocation for the corresponding virtqueue in find_vqs. 572 */ 573 vqs_info[VIRTIO_BALLOON_VQ_INFLATE].callback = balloon_ack; 574 vqs_info[VIRTIO_BALLOON_VQ_INFLATE].name = "inflate"; 575 vqs_info[VIRTIO_BALLOON_VQ_DEFLATE].callback = balloon_ack; 576 vqs_info[VIRTIO_BALLOON_VQ_DEFLATE].name = "deflate"; 577 578 if (virtio_has_feature(vb->vdev, VIRTIO_BALLOON_F_STATS_VQ)) { 579 vqs_info[VIRTIO_BALLOON_VQ_STATS].name = "stats"; 580 vqs_info[VIRTIO_BALLOON_VQ_STATS].callback = stats_request; 581 } 582 583 if (virtio_has_feature(vb->vdev, VIRTIO_BALLOON_F_FREE_PAGE_HINT)) 584 vqs_info[VIRTIO_BALLOON_VQ_FREE_PAGE].name = "free_page_vq"; 585 586 if (virtio_has_feature(vb->vdev, VIRTIO_BALLOON_F_REPORTING)) { 587 vqs_info[VIRTIO_BALLOON_VQ_REPORTING].name = "reporting_vq"; 588 vqs_info[VIRTIO_BALLOON_VQ_REPORTING].callback = balloon_ack; 589 } 590 591 err = virtio_find_vqs(vb->vdev, VIRTIO_BALLOON_VQ_MAX, vqs, 592 vqs_info, NULL); 593 if (err) 594 return err; 595 596 vb->inflate_vq = vqs[VIRTIO_BALLOON_VQ_INFLATE]; 597 vb->deflate_vq = vqs[VIRTIO_BALLOON_VQ_DEFLATE]; 598 if (virtio_has_feature(vb->vdev, VIRTIO_BALLOON_F_STATS_VQ)) { 599 struct scatterlist sg; 600 unsigned int num_stats; 601 vb->stats_vq = vqs[VIRTIO_BALLOON_VQ_STATS]; 602 603 /* 604 * Prime this virtqueue with one buffer so the hypervisor can 605 * use it to signal us later (it can't be broken yet!). 606 */ 607 num_stats = update_balloon_stats(vb); 608 609 sg_init_one(&sg, vb->stats, sizeof(vb->stats[0]) * num_stats); 610 err = virtqueue_add_outbuf(vb->stats_vq, &sg, 1, vb, 611 GFP_KERNEL); 612 if (err) { 613 dev_warn(&vb->vdev->dev, "%s: add stat_vq failed\n", 614 __func__); 615 return err; 616 } 617 virtqueue_kick(vb->stats_vq); 618 } 619 620 if (virtio_has_feature(vb->vdev, VIRTIO_BALLOON_F_FREE_PAGE_HINT)) 621 vb->free_page_vq = vqs[VIRTIO_BALLOON_VQ_FREE_PAGE]; 622 623 if (virtio_has_feature(vb->vdev, VIRTIO_BALLOON_F_REPORTING)) 624 vb->reporting_vq = vqs[VIRTIO_BALLOON_VQ_REPORTING]; 625 626 return 0; 627 } 628 629 static u32 virtio_balloon_cmd_id_received(struct virtio_balloon *vb) 630 { 631 if (test_and_clear_bit(VIRTIO_BALLOON_CONFIG_READ_CMD_ID, 632 &vb->config_read_bitmap)) { 633 /* Legacy balloon config space is LE, unlike all other devices. */ 634 virtio_cread_le(vb->vdev, struct virtio_balloon_config, 635 free_page_hint_cmd_id, 636 &vb->cmd_id_received_cache); 637 } 638 639 return vb->cmd_id_received_cache; 640 } 641 642 static int send_cmd_id_start(struct virtio_balloon *vb) 643 { 644 struct scatterlist sg; 645 struct virtqueue *vq = vb->free_page_vq; 646 int err, unused; 647 648 /* Detach all the used buffers from the vq */ 649 while (virtqueue_get_buf(vq, &unused)) 650 ; 651 652 vb->cmd_id_active = cpu_to_virtio32(vb->vdev, 653 virtio_balloon_cmd_id_received(vb)); 654 sg_init_one(&sg, &vb->cmd_id_active, sizeof(vb->cmd_id_active)); 655 err = virtqueue_add_outbuf(vq, &sg, 1, &vb->cmd_id_active, GFP_KERNEL); 656 if (!err) 657 virtqueue_kick(vq); 658 return err; 659 } 660 661 static int send_cmd_id_stop(struct virtio_balloon *vb) 662 { 663 struct scatterlist sg; 664 struct virtqueue *vq = vb->free_page_vq; 665 int err, unused; 666 667 /* Detach all the used buffers from the vq */ 668 while (virtqueue_get_buf(vq, &unused)) 669 ; 670 671 sg_init_one(&sg, &vb->cmd_id_stop, sizeof(vb->cmd_id_stop)); 672 err = virtqueue_add_outbuf(vq, &sg, 1, &vb->cmd_id_stop, GFP_KERNEL); 673 if (!err) 674 virtqueue_kick(vq); 675 return err; 676 } 677 678 static int get_free_page_and_send(struct virtio_balloon *vb) 679 { 680 struct virtqueue *vq = vb->free_page_vq; 681 struct page *page; 682 struct scatterlist sg; 683 int err, unused; 684 void *p; 685 686 /* Detach all the used buffers from the vq */ 687 while (virtqueue_get_buf(vq, &unused)) 688 ; 689 690 page = alloc_pages(VIRTIO_BALLOON_FREE_PAGE_ALLOC_FLAG, 691 VIRTIO_BALLOON_HINT_BLOCK_ORDER); 692 /* 693 * When the allocation returns NULL, it indicates that we have got all 694 * the possible free pages, so return -EINTR to stop. 695 */ 696 if (!page) 697 return -EINTR; 698 699 p = page_address(page); 700 sg_init_one(&sg, p, VIRTIO_BALLOON_HINT_BLOCK_BYTES); 701 /* There is always 1 entry reserved for the cmd id to use. */ 702 if (vq->num_free > 1) { 703 err = virtqueue_add_inbuf(vq, &sg, 1, p, GFP_KERNEL); 704 if (unlikely(err)) { 705 free_pages((unsigned long)p, 706 VIRTIO_BALLOON_HINT_BLOCK_ORDER); 707 return err; 708 } 709 virtqueue_kick(vq); 710 spin_lock_irq(&vb->free_page_list_lock); 711 balloon_page_push(&vb->free_page_list, page); 712 vb->num_free_page_blocks++; 713 spin_unlock_irq(&vb->free_page_list_lock); 714 } else { 715 /* 716 * The vq has no available entry to add this page block, so 717 * just free it. 718 */ 719 free_pages((unsigned long)p, VIRTIO_BALLOON_HINT_BLOCK_ORDER); 720 } 721 722 return 0; 723 } 724 725 static int send_free_pages(struct virtio_balloon *vb) 726 { 727 int err; 728 u32 cmd_id_active; 729 730 while (1) { 731 /* 732 * If a stop id or a new cmd id was just received from host, 733 * stop the reporting. 734 */ 735 cmd_id_active = virtio32_to_cpu(vb->vdev, vb->cmd_id_active); 736 if (unlikely(cmd_id_active != 737 virtio_balloon_cmd_id_received(vb))) 738 break; 739 740 /* 741 * The free page blocks are allocated and sent to host one by 742 * one. 743 */ 744 err = get_free_page_and_send(vb); 745 if (err == -EINTR) 746 break; 747 else if (unlikely(err)) 748 return err; 749 } 750 751 return 0; 752 } 753 754 static void virtio_balloon_report_free_page(struct virtio_balloon *vb) 755 { 756 int err; 757 struct device *dev = &vb->vdev->dev; 758 759 /* Start by sending the received cmd id to host with an outbuf. */ 760 err = send_cmd_id_start(vb); 761 if (unlikely(err)) 762 dev_err(dev, "Failed to send a start id, err = %d\n", err); 763 764 err = send_free_pages(vb); 765 if (unlikely(err)) 766 dev_err(dev, "Failed to send a free page, err = %d\n", err); 767 768 /* End by sending a stop id to host with an outbuf. */ 769 err = send_cmd_id_stop(vb); 770 if (unlikely(err)) 771 dev_err(dev, "Failed to send a stop id, err = %d\n", err); 772 } 773 774 static void report_free_page_func(struct work_struct *work) 775 { 776 struct virtio_balloon *vb = container_of(work, struct virtio_balloon, 777 report_free_page_work); 778 u32 cmd_id_received; 779 780 cmd_id_received = virtio_balloon_cmd_id_received(vb); 781 if (cmd_id_received == VIRTIO_BALLOON_CMD_ID_DONE) { 782 /* Pass ULONG_MAX to give back all the free pages */ 783 return_free_pages_to_mm(vb, ULONG_MAX); 784 } else if (cmd_id_received != VIRTIO_BALLOON_CMD_ID_STOP && 785 cmd_id_received != 786 virtio32_to_cpu(vb->vdev, vb->cmd_id_active)) { 787 virtio_balloon_report_free_page(vb); 788 } 789 } 790 791 #ifdef CONFIG_BALLOON_COMPACTION 792 /* 793 * virtballoon_migratepage - perform the balloon page migration on behalf of 794 * a compaction thread. (called under page lock) 795 * @vb_dev_info: the balloon device 796 * @newpage: page that will replace the isolated page after migration finishes. 797 * @page : the isolated (old) page that is about to be migrated to newpage. 798 * @mode : compaction mode -- not used for balloon page migration. 799 * 800 * After a ballooned page gets isolated by compaction procedures, this is the 801 * function that performs the page migration on behalf of a compaction thread 802 * The page migration for virtio balloon is done in a simple swap fashion which 803 * follows these two macro steps: 804 * 1) insert newpage into vb->pages list and update the host about it; 805 * 2) update the host about the old page removed from vb->pages list; 806 * 807 * This function preforms the balloon page migration task. 808 * Called through movable_operations->migrate_page 809 */ 810 static int virtballoon_migratepage(struct balloon_dev_info *vb_dev_info, 811 struct page *newpage, struct page *page, enum migrate_mode mode) 812 { 813 struct virtio_balloon *vb = container_of(vb_dev_info, 814 struct virtio_balloon, vb_dev_info); 815 unsigned long flags; 816 817 /* 818 * In order to avoid lock contention while migrating pages concurrently 819 * to leak_balloon() or fill_balloon() we just give up the balloon_lock 820 * this turn, as it is easier to retry the page migration later. 821 * This also prevents fill_balloon() getting stuck into a mutex 822 * recursion in the case it ends up triggering memory compaction 823 * while it is attempting to inflate the ballon. 824 */ 825 if (!mutex_trylock(&vb->balloon_lock)) 826 return -EAGAIN; 827 828 get_page(newpage); /* balloon reference */ 829 830 /* 831 * When we migrate a page to a different zone and adjusted the 832 * managed page count when inflating, we have to fixup the count of 833 * both involved zones. 834 */ 835 if (!virtio_has_feature(vb->vdev, VIRTIO_BALLOON_F_DEFLATE_ON_OOM) && 836 page_zone(page) != page_zone(newpage)) { 837 adjust_managed_page_count(page, 1); 838 adjust_managed_page_count(newpage, -1); 839 } 840 841 /* balloon's page migration 1st step -- inflate "newpage" */ 842 spin_lock_irqsave(&vb_dev_info->pages_lock, flags); 843 balloon_page_insert(vb_dev_info, newpage); 844 vb_dev_info->isolated_pages--; 845 __count_vm_event(BALLOON_MIGRATE); 846 spin_unlock_irqrestore(&vb_dev_info->pages_lock, flags); 847 vb->num_pfns = VIRTIO_BALLOON_PAGES_PER_PAGE; 848 set_page_pfns(vb, vb->pfns, newpage); 849 tell_host(vb, vb->inflate_vq); 850 851 /* balloon's page migration 2nd step -- deflate "page" */ 852 spin_lock_irqsave(&vb_dev_info->pages_lock, flags); 853 balloon_page_delete(page); 854 spin_unlock_irqrestore(&vb_dev_info->pages_lock, flags); 855 vb->num_pfns = VIRTIO_BALLOON_PAGES_PER_PAGE; 856 set_page_pfns(vb, vb->pfns, page); 857 tell_host(vb, vb->deflate_vq); 858 859 mutex_unlock(&vb->balloon_lock); 860 861 put_page(page); /* balloon reference */ 862 863 return MIGRATEPAGE_SUCCESS; 864 } 865 #endif /* CONFIG_BALLOON_COMPACTION */ 866 867 static unsigned long shrink_free_pages(struct virtio_balloon *vb, 868 unsigned long pages_to_free) 869 { 870 unsigned long blocks_to_free, blocks_freed; 871 872 pages_to_free = round_up(pages_to_free, 873 VIRTIO_BALLOON_HINT_BLOCK_PAGES); 874 blocks_to_free = pages_to_free / VIRTIO_BALLOON_HINT_BLOCK_PAGES; 875 blocks_freed = return_free_pages_to_mm(vb, blocks_to_free); 876 877 return blocks_freed * VIRTIO_BALLOON_HINT_BLOCK_PAGES; 878 } 879 880 static unsigned long virtio_balloon_shrinker_scan(struct shrinker *shrinker, 881 struct shrink_control *sc) 882 { 883 struct virtio_balloon *vb = shrinker->private_data; 884 885 return shrink_free_pages(vb, sc->nr_to_scan); 886 } 887 888 static unsigned long virtio_balloon_shrinker_count(struct shrinker *shrinker, 889 struct shrink_control *sc) 890 { 891 struct virtio_balloon *vb = shrinker->private_data; 892 893 return vb->num_free_page_blocks * VIRTIO_BALLOON_HINT_BLOCK_PAGES; 894 } 895 896 static int virtio_balloon_oom_notify(struct notifier_block *nb, 897 unsigned long dummy, void *parm) 898 { 899 struct virtio_balloon *vb = container_of(nb, 900 struct virtio_balloon, oom_nb); 901 unsigned long *freed = parm; 902 903 *freed += leak_balloon(vb, VIRTIO_BALLOON_OOM_NR_PAGES) / 904 VIRTIO_BALLOON_PAGES_PER_PAGE; 905 update_balloon_size(vb); 906 907 return NOTIFY_OK; 908 } 909 910 static void virtio_balloon_unregister_shrinker(struct virtio_balloon *vb) 911 { 912 shrinker_free(vb->shrinker); 913 } 914 915 static int virtio_balloon_register_shrinker(struct virtio_balloon *vb) 916 { 917 vb->shrinker = shrinker_alloc(0, "virtio-balloon"); 918 if (!vb->shrinker) 919 return -ENOMEM; 920 921 vb->shrinker->scan_objects = virtio_balloon_shrinker_scan; 922 vb->shrinker->count_objects = virtio_balloon_shrinker_count; 923 vb->shrinker->private_data = vb; 924 925 shrinker_register(vb->shrinker); 926 927 return 0; 928 } 929 930 static int virtballoon_probe(struct virtio_device *vdev) 931 { 932 struct virtio_balloon *vb; 933 int err; 934 935 if (!vdev->config->get) { 936 dev_err(&vdev->dev, "%s failure: config access disabled\n", 937 __func__); 938 return -EINVAL; 939 } 940 941 vdev->priv = vb = kzalloc(sizeof(*vb), GFP_KERNEL); 942 if (!vb) { 943 err = -ENOMEM; 944 goto out; 945 } 946 947 INIT_WORK(&vb->update_balloon_stats_work, update_balloon_stats_func); 948 INIT_WORK(&vb->update_balloon_size_work, update_balloon_size_func); 949 spin_lock_init(&vb->stop_update_lock); 950 mutex_init(&vb->balloon_lock); 951 init_waitqueue_head(&vb->acked); 952 vb->vdev = vdev; 953 954 balloon_devinfo_init(&vb->vb_dev_info); 955 956 err = init_vqs(vb); 957 if (err) 958 goto out_free_vb; 959 960 #ifdef CONFIG_BALLOON_COMPACTION 961 vb->vb_dev_info.migratepage = virtballoon_migratepage; 962 #endif 963 if (virtio_has_feature(vdev, VIRTIO_BALLOON_F_FREE_PAGE_HINT)) { 964 /* 965 * There is always one entry reserved for cmd id, so the ring 966 * size needs to be at least two to report free page hints. 967 */ 968 if (virtqueue_get_vring_size(vb->free_page_vq) < 2) { 969 err = -ENOSPC; 970 goto out_del_vqs; 971 } 972 vb->balloon_wq = alloc_workqueue("balloon-wq", 973 WQ_FREEZABLE | WQ_CPU_INTENSIVE, 0); 974 if (!vb->balloon_wq) { 975 err = -ENOMEM; 976 goto out_del_vqs; 977 } 978 INIT_WORK(&vb->report_free_page_work, report_free_page_func); 979 vb->cmd_id_received_cache = VIRTIO_BALLOON_CMD_ID_STOP; 980 vb->cmd_id_active = cpu_to_virtio32(vb->vdev, 981 VIRTIO_BALLOON_CMD_ID_STOP); 982 vb->cmd_id_stop = cpu_to_virtio32(vb->vdev, 983 VIRTIO_BALLOON_CMD_ID_STOP); 984 spin_lock_init(&vb->free_page_list_lock); 985 INIT_LIST_HEAD(&vb->free_page_list); 986 /* 987 * We're allowed to reuse any free pages, even if they are 988 * still to be processed by the host. 989 */ 990 err = virtio_balloon_register_shrinker(vb); 991 if (err) 992 goto out_del_balloon_wq; 993 } 994 995 if (virtio_has_feature(vb->vdev, VIRTIO_BALLOON_F_DEFLATE_ON_OOM)) { 996 vb->oom_nb.notifier_call = virtio_balloon_oom_notify; 997 vb->oom_nb.priority = VIRTIO_BALLOON_OOM_NOTIFY_PRIORITY; 998 err = register_oom_notifier(&vb->oom_nb); 999 if (err < 0) 1000 goto out_unregister_shrinker; 1001 } 1002 1003 if (virtio_has_feature(vdev, VIRTIO_BALLOON_F_PAGE_POISON)) { 1004 /* Start with poison val of 0 representing general init */ 1005 __u32 poison_val = 0; 1006 1007 /* 1008 * Let the hypervisor know that we are expecting a 1009 * specific value to be written back in balloon pages. 1010 * 1011 * If the PAGE_POISON value was larger than a byte we would 1012 * need to byte swap poison_val here to guarantee it is 1013 * little-endian. However for now it is a single byte so we 1014 * can pass it as-is. 1015 */ 1016 if (!want_init_on_free()) 1017 memset(&poison_val, PAGE_POISON, sizeof(poison_val)); 1018 1019 virtio_cwrite_le(vb->vdev, struct virtio_balloon_config, 1020 poison_val, &poison_val); 1021 } 1022 1023 vb->pr_dev_info.report = virtballoon_free_page_report; 1024 if (virtio_has_feature(vb->vdev, VIRTIO_BALLOON_F_REPORTING)) { 1025 unsigned int capacity; 1026 1027 capacity = virtqueue_get_vring_size(vb->reporting_vq); 1028 if (capacity < PAGE_REPORTING_CAPACITY) { 1029 err = -ENOSPC; 1030 goto out_unregister_oom; 1031 } 1032 1033 /* 1034 * The default page reporting order is @pageblock_order, which 1035 * corresponds to 512MB in size on ARM64 when 64KB base page 1036 * size is used. The page reporting won't be triggered if the 1037 * freeing page can't come up with a free area like that huge. 1038 * So we specify the page reporting order to 5, corresponding 1039 * to 2MB. It helps to avoid THP splitting if 4KB base page 1040 * size is used by host. 1041 * 1042 * Ideally, the page reporting order is selected based on the 1043 * host's base page size. However, it needs more work to report 1044 * that value. The hard-coded order would be fine currently. 1045 */ 1046 #if defined(CONFIG_ARM64) && defined(CONFIG_ARM64_64K_PAGES) 1047 vb->pr_dev_info.order = 5; 1048 #endif 1049 1050 err = page_reporting_register(&vb->pr_dev_info); 1051 if (err) 1052 goto out_unregister_oom; 1053 } 1054 1055 spin_lock_init(&vb->wakeup_lock); 1056 1057 /* 1058 * The virtio balloon itself can't wake up the device, but it is 1059 * responsible for processing wakeup events passed up from the transport 1060 * layer. Wakeup sources don't support nesting/chaining calls, so we use 1061 * our own wakeup source to ensure wakeup events are properly handled 1062 * without trampling on the transport layer's wakeup source. 1063 */ 1064 device_set_wakeup_capable(&vb->vdev->dev, true); 1065 1066 virtio_device_ready(vdev); 1067 1068 if (towards_target(vb)) 1069 virtballoon_changed(vdev); 1070 return 0; 1071 1072 out_unregister_oom: 1073 if (virtio_has_feature(vb->vdev, VIRTIO_BALLOON_F_DEFLATE_ON_OOM)) 1074 unregister_oom_notifier(&vb->oom_nb); 1075 out_unregister_shrinker: 1076 if (virtio_has_feature(vb->vdev, VIRTIO_BALLOON_F_FREE_PAGE_HINT)) 1077 virtio_balloon_unregister_shrinker(vb); 1078 out_del_balloon_wq: 1079 if (virtio_has_feature(vdev, VIRTIO_BALLOON_F_FREE_PAGE_HINT)) 1080 destroy_workqueue(vb->balloon_wq); 1081 out_del_vqs: 1082 vdev->config->del_vqs(vdev); 1083 out_free_vb: 1084 kfree(vb); 1085 out: 1086 return err; 1087 } 1088 1089 static void remove_common(struct virtio_balloon *vb) 1090 { 1091 /* There might be pages left in the balloon: free them. */ 1092 while (vb->num_pages) 1093 leak_balloon(vb, vb->num_pages); 1094 update_balloon_size(vb); 1095 1096 /* There might be free pages that are being reported: release them. */ 1097 if (virtio_has_feature(vb->vdev, VIRTIO_BALLOON_F_FREE_PAGE_HINT)) 1098 return_free_pages_to_mm(vb, ULONG_MAX); 1099 1100 /* Now we reset the device so we can clean up the queues. */ 1101 virtio_reset_device(vb->vdev); 1102 1103 vb->vdev->config->del_vqs(vb->vdev); 1104 } 1105 1106 static void virtballoon_remove(struct virtio_device *vdev) 1107 { 1108 struct virtio_balloon *vb = vdev->priv; 1109 1110 if (virtio_has_feature(vb->vdev, VIRTIO_BALLOON_F_REPORTING)) 1111 page_reporting_unregister(&vb->pr_dev_info); 1112 if (virtio_has_feature(vb->vdev, VIRTIO_BALLOON_F_DEFLATE_ON_OOM)) 1113 unregister_oom_notifier(&vb->oom_nb); 1114 if (virtio_has_feature(vb->vdev, VIRTIO_BALLOON_F_FREE_PAGE_HINT)) 1115 virtio_balloon_unregister_shrinker(vb); 1116 spin_lock_irq(&vb->stop_update_lock); 1117 vb->stop_update = true; 1118 spin_unlock_irq(&vb->stop_update_lock); 1119 cancel_work_sync(&vb->update_balloon_size_work); 1120 cancel_work_sync(&vb->update_balloon_stats_work); 1121 1122 if (virtio_has_feature(vdev, VIRTIO_BALLOON_F_FREE_PAGE_HINT)) { 1123 cancel_work_sync(&vb->report_free_page_work); 1124 destroy_workqueue(vb->balloon_wq); 1125 } 1126 1127 remove_common(vb); 1128 kfree(vb); 1129 } 1130 1131 #ifdef CONFIG_PM_SLEEP 1132 static int virtballoon_freeze(struct virtio_device *vdev) 1133 { 1134 struct virtio_balloon *vb = vdev->priv; 1135 1136 /* 1137 * The workqueue is already frozen by the PM core before this 1138 * function is called. 1139 */ 1140 remove_common(vb); 1141 return 0; 1142 } 1143 1144 static int virtballoon_restore(struct virtio_device *vdev) 1145 { 1146 struct virtio_balloon *vb = vdev->priv; 1147 int ret; 1148 1149 ret = init_vqs(vdev->priv); 1150 if (ret) 1151 return ret; 1152 1153 virtio_device_ready(vdev); 1154 1155 if (towards_target(vb)) 1156 virtballoon_changed(vdev); 1157 update_balloon_size(vb); 1158 return 0; 1159 } 1160 #endif 1161 1162 static int virtballoon_validate(struct virtio_device *vdev) 1163 { 1164 /* 1165 * Inform the hypervisor that our pages are poisoned or 1166 * initialized. If we cannot do that then we should disable 1167 * page reporting as it could potentially change the contents 1168 * of our free pages. 1169 */ 1170 if (!want_init_on_free() && !page_poisoning_enabled_static()) 1171 __virtio_clear_bit(vdev, VIRTIO_BALLOON_F_PAGE_POISON); 1172 else if (!virtio_has_feature(vdev, VIRTIO_BALLOON_F_PAGE_POISON)) 1173 __virtio_clear_bit(vdev, VIRTIO_BALLOON_F_REPORTING); 1174 1175 __virtio_clear_bit(vdev, VIRTIO_F_ACCESS_PLATFORM); 1176 return 0; 1177 } 1178 1179 static unsigned int features[] = { 1180 VIRTIO_BALLOON_F_MUST_TELL_HOST, 1181 VIRTIO_BALLOON_F_STATS_VQ, 1182 VIRTIO_BALLOON_F_DEFLATE_ON_OOM, 1183 VIRTIO_BALLOON_F_FREE_PAGE_HINT, 1184 VIRTIO_BALLOON_F_PAGE_POISON, 1185 VIRTIO_BALLOON_F_REPORTING, 1186 }; 1187 1188 static struct virtio_driver virtio_balloon_driver = { 1189 .feature_table = features, 1190 .feature_table_size = ARRAY_SIZE(features), 1191 .driver.name = KBUILD_MODNAME, 1192 .id_table = id_table, 1193 .validate = virtballoon_validate, 1194 .probe = virtballoon_probe, 1195 .remove = virtballoon_remove, 1196 .config_changed = virtballoon_changed, 1197 #ifdef CONFIG_PM_SLEEP 1198 .freeze = virtballoon_freeze, 1199 .restore = virtballoon_restore, 1200 #endif 1201 }; 1202 1203 module_virtio_driver(virtio_balloon_driver); 1204 MODULE_DEVICE_TABLE(virtio, id_table); 1205 MODULE_DESCRIPTION("Virtio balloon driver"); 1206 MODULE_LICENSE("GPL"); 1207