drivers/virtio/virtio_balloon.c

   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/wait.h>
  18 #include <linux/mm.h>
  19 #include <linux/mount.h>
  20 #include <linux/magic.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)(PAGE_SIZE >> VIRTIO_BALLOON_PFN_SHIFT)
  28 #define VIRTIO_BALLOON_ARRAY_PFNS_MAX 256
  29 #define VIRTBALLOON_OOM_NOTIFY_PRIORITY 80
  30
  31 #define VIRTIO_BALLOON_FREE_PAGE_ALLOC_FLAG (__GFP_NORETRY | __GFP_NOWARN | \
  32                                              __GFP_NOMEMALLOC)
  33 /* The order of free page blocks to report to host */
  34 #define VIRTIO_BALLOON_FREE_PAGE_ORDER (MAX_ORDER - 1)
  35 /* The size of a free page block in bytes */
  36 #define VIRTIO_BALLOON_FREE_PAGE_SIZE \
  37         (1 << (VIRTIO_BALLOON_FREE_PAGE_ORDER + PAGE_SHIFT))
  38
  39 #ifdef CONFIG_BALLOON_COMPACTION
  40 static struct vfsmount *balloon_mnt;
  41 #endif
  42
  43 enum virtio_balloon_vq {
  44         VIRTIO_BALLOON_VQ_INFLATE,
  45         VIRTIO_BALLOON_VQ_DEFLATE,
  46         VIRTIO_BALLOON_VQ_STATS,
  47         VIRTIO_BALLOON_VQ_FREE_PAGE,
  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         /* To register a shrinker to shrink memory upon memory pressure */
 114         struct shrinker shrinker;
 115 };
 116
 117 static struct virtio_device_id id_table[] = {
 118         { VIRTIO_ID_BALLOON, VIRTIO_DEV_ANY_ID },
 119         { 0 },
 120 };
 121
 122 static u32 page_to_balloon_pfn(struct page *page)
 123 {
 124         unsigned long pfn = page_to_pfn(page);
 125
 126         BUILD_BUG_ON(PAGE_SHIFT < VIRTIO_BALLOON_PFN_SHIFT);
 127         /* Convert pfn from Linux page size to balloon page size. */
 128         return pfn * VIRTIO_BALLOON_PAGES_PER_PAGE;
 129 }
 130
 131 static void balloon_ack(struct virtqueue *vq)
 132 {
 133         struct virtio_balloon *vb = vq->vdev->priv;
 134
 135         wake_up(&vb->acked);
 136 }
 137
 138 static void tell_host(struct virtio_balloon *vb, struct virtqueue *vq)
 139 {
 140         struct scatterlist sg;
 141         unsigned int len;
 142
 143         sg_init_one(&sg, vb->pfns, sizeof(vb->pfns[0]) * vb->num_pfns);
 144
 145         /* We should always be able to add one buffer to an empty queue. */
 146         virtqueue_add_outbuf(vq, &sg, 1, vb, GFP_KERNEL);
 147         virtqueue_kick(vq);
 148
 149         /* When host has read buffer, this completes via balloon_ack */
 150         wait_event(vb->acked, virtqueue_get_buf(vq, &len));
 151
 152 }
 153
 154 static void set_page_pfns(struct virtio_balloon *vb,
 155                           __virtio32 pfns[], struct page *page)
 156 {
 157         unsigned int i;
 158
 159         /*
 160          * Set balloon pfns pointing at this page.
 161          * Note that the first pfn points at start of the page.
 162          */
 163         for (i = 0; i < VIRTIO_BALLOON_PAGES_PER_PAGE; i++)
 164                 pfns[i] = cpu_to_virtio32(vb->vdev,
 165                                           page_to_balloon_pfn(page) + i);
 166 }
 167
 168 static unsigned fill_balloon(struct virtio_balloon *vb, size_t num)
 169 {
 170         unsigned num_allocated_pages;
 171         unsigned num_pfns;
 172         struct page *page;
 173         LIST_HEAD(pages);
 174
 175         /* We can only do one array worth at a time. */
 176         num = min(num, ARRAY_SIZE(vb->pfns));
 177
 178         for (num_pfns = 0; num_pfns < num;
 179              num_pfns += VIRTIO_BALLOON_PAGES_PER_PAGE) {
 180                 struct page *page = balloon_page_alloc();
 181
 182                 if (!page) {
 183                         dev_info_ratelimited(&vb->vdev->dev,
 184                                              "Out of puff! Can't get %u pages\n",
 185                                              VIRTIO_BALLOON_PAGES_PER_PAGE);
 186                         /* Sleep for at least 1/5 of a second before retry. */
 187                         msleep(200);
 188                         break;
 189                 }
 190
 191                 balloon_page_push(&pages, page);
 192         }
 193
 194         mutex_lock(&vb->balloon_lock);
 195
 196         vb->num_pfns = 0;
 197
 198         while ((page = balloon_page_pop(&pages))) {
 199                 balloon_page_enqueue(&vb->vb_dev_info, page);
 200
 201                 set_page_pfns(vb, vb->pfns + vb->num_pfns, page);
 202                 vb->num_pages += VIRTIO_BALLOON_PAGES_PER_PAGE;
 203                 if (!virtio_has_feature(vb->vdev,
 204                                         VIRTIO_BALLOON_F_DEFLATE_ON_OOM))
 205                         adjust_managed_page_count(page, -1);
 206                 vb->num_pfns += VIRTIO_BALLOON_PAGES_PER_PAGE;
 207         }
 208
 209         num_allocated_pages = vb->num_pfns;
 210         /* Did we get any? */
 211         if (vb->num_pfns != 0)
 212                 tell_host(vb, vb->inflate_vq);
 213         mutex_unlock(&vb->balloon_lock);
 214
 215         return num_allocated_pages;
 216 }
 217
 218 static void release_pages_balloon(struct virtio_balloon *vb,
 219                                  struct list_head *pages)
 220 {
 221         struct page *page, *next;
 222
 223         list_for_each_entry_safe(page, next, pages, lru) {
 224                 if (!virtio_has_feature(vb->vdev,
 225                                         VIRTIO_BALLOON_F_DEFLATE_ON_OOM))
 226                         adjust_managed_page_count(page, 1);
 227                 list_del(&page->lru);
 228                 put_page(page); /* balloon reference */
 229         }
 230 }
 231
 232 static unsigned leak_balloon(struct virtio_balloon *vb, size_t num)
 233 {
 234         unsigned num_freed_pages;
 235         struct page *page;
 236         struct balloon_dev_info *vb_dev_info = &vb->vb_dev_info;
 237         LIST_HEAD(pages);
 238
 239         /* We can only do one array worth at a time. */
 240         num = min(num, ARRAY_SIZE(vb->pfns));
 241
 242         mutex_lock(&vb->balloon_lock);
 243         /* We can't release more pages than taken */
 244         num = min(num, (size_t)vb->num_pages);
 245         for (vb->num_pfns = 0; vb->num_pfns < num;
 246              vb->num_pfns += VIRTIO_BALLOON_PAGES_PER_PAGE) {
 247                 page = balloon_page_dequeue(vb_dev_info);
 248                 if (!page)
 249                         break;
 250                 set_page_pfns(vb, vb->pfns + vb->num_pfns, page);
 251                 list_add(&page->lru, &pages);
 252                 vb->num_pages -= VIRTIO_BALLOON_PAGES_PER_PAGE;
 253         }
 254
 255         num_freed_pages = vb->num_pfns;
 256         /*
 257          * Note that if
 258          * virtio_has_feature(vdev, VIRTIO_BALLOON_F_MUST_TELL_HOST);
 259          * is true, we *have* to do it in this order
 260          */
 261         if (vb->num_pfns != 0)
 262                 tell_host(vb, vb->deflate_vq);
 263         release_pages_balloon(vb, &pages);
 264         mutex_unlock(&vb->balloon_lock);
 265         return num_freed_pages;
 266 }
 267
 268 static inline void update_stat(struct virtio_balloon *vb, int idx,
 269                                u16 tag, u64 val)
 270 {
 271         BUG_ON(idx >= VIRTIO_BALLOON_S_NR);
 272         vb->stats[idx].tag = cpu_to_virtio16(vb->vdev, tag);
 273         vb->stats[idx].val = cpu_to_virtio64(vb->vdev, val);
 274 }
 275
 276 #define pages_to_bytes(x) ((u64)(x) << PAGE_SHIFT)
 277
 278 static unsigned int update_balloon_stats(struct virtio_balloon *vb)
 279 {
 280         unsigned long events[NR_VM_EVENT_ITEMS];
 281         struct sysinfo i;
 282         unsigned int idx = 0;
 283         long available;
 284         unsigned long caches;
 285
 286         all_vm_events(events);
 287         si_meminfo(&i);
 288
 289         available = si_mem_available();
 290         caches = global_node_page_state(NR_FILE_PAGES);
 291
 292 #ifdef CONFIG_VM_EVENT_COUNTERS
 293         update_stat(vb, idx++, VIRTIO_BALLOON_S_SWAP_IN,
 294                                 pages_to_bytes(events[PSWPIN]));
 295         update_stat(vb, idx++, VIRTIO_BALLOON_S_SWAP_OUT,
 296                                 pages_to_bytes(events[PSWPOUT]));
 297         update_stat(vb, idx++, VIRTIO_BALLOON_S_MAJFLT, events[PGMAJFAULT]);
 298         update_stat(vb, idx++, VIRTIO_BALLOON_S_MINFLT, events[PGFAULT]);
 299 #ifdef CONFIG_HUGETLB_PAGE
 300         update_stat(vb, idx++, VIRTIO_BALLOON_S_HTLB_PGALLOC,
 301                     events[HTLB_BUDDY_PGALLOC]);
 302         update_stat(vb, idx++, VIRTIO_BALLOON_S_HTLB_PGFAIL,
 303                     events[HTLB_BUDDY_PGALLOC_FAIL]);
 304 #endif
 305 #endif
 306         update_stat(vb, idx++, VIRTIO_BALLOON_S_MEMFREE,
 307                                 pages_to_bytes(i.freeram));
 308         update_stat(vb, idx++, VIRTIO_BALLOON_S_MEMTOT,
 309                                 pages_to_bytes(i.totalram));
 310         update_stat(vb, idx++, VIRTIO_BALLOON_S_AVAIL,
 311                                 pages_to_bytes(available));
 312         update_stat(vb, idx++, VIRTIO_BALLOON_S_CACHES,
 313                                 pages_to_bytes(caches));
 314
 315         return idx;
 316 }
 317
 318 /*
 319  * While most virtqueues communicate guest-initiated requests to the hypervisor,
 320  * the stats queue operates in reverse.  The driver initializes the virtqueue
 321  * with a single buffer.  From that point forward, all conversations consist of
 322  * a hypervisor request (a call to this function) which directs us to refill
 323  * the virtqueue with a fresh stats buffer.  Since stats collection can sleep,
 324  * we delegate the job to a freezable workqueue that will do the actual work via
 325  * stats_handle_request().
 326  */
 327 static void stats_request(struct virtqueue *vq)
 328 {
 329         struct virtio_balloon *vb = vq->vdev->priv;
 330
 331         spin_lock(&vb->stop_update_lock);
 332         if (!vb->stop_update)
 333                 queue_work(system_freezable_wq, &vb->update_balloon_stats_work);
 334         spin_unlock(&vb->stop_update_lock);
 335 }
 336
 337 static void stats_handle_request(struct virtio_balloon *vb)
 338 {
 339         struct virtqueue *vq;
 340         struct scatterlist sg;
 341         unsigned int len, num_stats;
 342
 343         num_stats = update_balloon_stats(vb);
 344
 345         vq = vb->stats_vq;
 346         if (!virtqueue_get_buf(vq, &len))
 347                 return;
 348         sg_init_one(&sg, vb->stats, sizeof(vb->stats[0]) * num_stats);
 349         virtqueue_add_outbuf(vq, &sg, 1, vb, GFP_KERNEL);
 350         virtqueue_kick(vq);
 351 }
 352
 353 static inline s64 towards_target(struct virtio_balloon *vb)
 354 {
 355         s64 target;
 356         u32 num_pages;
 357
 358         virtio_cread(vb->vdev, struct virtio_balloon_config, num_pages,
 359                      &num_pages);
 360
 361         /* Legacy balloon config space is LE, unlike all other devices. */
 362         if (!virtio_has_feature(vb->vdev, VIRTIO_F_VERSION_1))
 363                 num_pages = le32_to_cpu((__force __le32)num_pages);
 364
 365         target = num_pages;
 366         return target - vb->num_pages;
 367 }
 368
 369 /* Gives back @num_to_return blocks of free pages to mm. */
 370 static unsigned long return_free_pages_to_mm(struct virtio_balloon *vb,
 371                                              unsigned long num_to_return)
 372 {
 373         struct page *page;
 374         unsigned long num_returned;
 375
 376         spin_lock_irq(&vb->free_page_list_lock);
 377         for (num_returned = 0; num_returned < num_to_return; num_returned++) {
 378                 page = balloon_page_pop(&vb->free_page_list);
 379                 if (!page)
 380                         break;
 381                 free_pages((unsigned long)page_address(page),
 382                            VIRTIO_BALLOON_FREE_PAGE_ORDER);
 383         }
 384         vb->num_free_page_blocks -= num_returned;
 385         spin_unlock_irq(&vb->free_page_list_lock);
 386
 387         return num_returned;
 388 }
 389
 390 static void virtio_balloon_queue_free_page_work(struct virtio_balloon *vb)
 391 {
 392         if (!virtio_has_feature(vb->vdev, VIRTIO_BALLOON_F_FREE_PAGE_HINT))
 393                 return;
 394
 395         /* No need to queue the work if the bit was already set. */
 396         if (test_and_set_bit(VIRTIO_BALLOON_CONFIG_READ_CMD_ID,
 397                              &vb->config_read_bitmap))
 398                 return;
 399
 400         queue_work(vb->balloon_wq, &vb->report_free_page_work);
 401 }
 402
 403 static void virtballoon_changed(struct virtio_device *vdev)
 404 {
 405         struct virtio_balloon *vb = vdev->priv;
 406         unsigned long flags;
 407
 408         spin_lock_irqsave(&vb->stop_update_lock, flags);
 409         if (!vb->stop_update) {
 410                 queue_work(system_freezable_wq,
 411                            &vb->update_balloon_size_work);
 412                 virtio_balloon_queue_free_page_work(vb);
 413         }
 414         spin_unlock_irqrestore(&vb->stop_update_lock, flags);
 415 }
 416
 417 static void update_balloon_size(struct virtio_balloon *vb)
 418 {
 419         u32 actual = vb->num_pages;
 420
 421         /* Legacy balloon config space is LE, unlike all other devices. */
 422         if (!virtio_has_feature(vb->vdev, VIRTIO_F_VERSION_1))
 423                 actual = (__force u32)cpu_to_le32(actual);
 424
 425         virtio_cwrite(vb->vdev, struct virtio_balloon_config, actual,
 426                       &actual);
 427 }
 428
 429 static void update_balloon_stats_func(struct work_struct *work)
 430 {
 431         struct virtio_balloon *vb;
 432
 433         vb = container_of(work, struct virtio_balloon,
 434                           update_balloon_stats_work);
 435         stats_handle_request(vb);
 436 }
 437
 438 static void update_balloon_size_func(struct work_struct *work)
 439 {
 440         struct virtio_balloon *vb;
 441         s64 diff;
 442
 443         vb = container_of(work, struct virtio_balloon,
 444                           update_balloon_size_work);
 445         diff = towards_target(vb);
 446
 447         if (!diff)
 448                 return;
 449
 450         if (diff > 0)
 451                 diff -= fill_balloon(vb, diff);
 452         else
 453                 diff += leak_balloon(vb, -diff);
 454         update_balloon_size(vb);
 455
 456         if (diff)
 457                 queue_work(system_freezable_wq, work);
 458 }
 459
 460 static int init_vqs(struct virtio_balloon *vb)
 461 {
 462         struct virtqueue *vqs[VIRTIO_BALLOON_VQ_MAX];
 463         vq_callback_t *callbacks[VIRTIO_BALLOON_VQ_MAX];
 464         const char *names[VIRTIO_BALLOON_VQ_MAX];
 465         int err;
 466
 467         /*
 468          * Inflateq and deflateq are used unconditionally. The names[]
 469          * will be NULL if the related feature is not enabled, which will
 470          * cause no allocation for the corresponding virtqueue in find_vqs.
 471          */
 472         callbacks[VIRTIO_BALLOON_VQ_INFLATE] = balloon_ack;
 473         names[VIRTIO_BALLOON_VQ_INFLATE] = "inflate";
 474         callbacks[VIRTIO_BALLOON_VQ_DEFLATE] = balloon_ack;
 475         names[VIRTIO_BALLOON_VQ_DEFLATE] = "deflate";
 476         names[VIRTIO_BALLOON_VQ_STATS] = NULL;
 477         names[VIRTIO_BALLOON_VQ_FREE_PAGE] = NULL;
 478
 479         if (virtio_has_feature(vb->vdev, VIRTIO_BALLOON_F_STATS_VQ)) {
 480                 names[VIRTIO_BALLOON_VQ_STATS] = "stats";
 481                 callbacks[VIRTIO_BALLOON_VQ_STATS] = stats_request;
 482         }
 483
 484         if (virtio_has_feature(vb->vdev, VIRTIO_BALLOON_F_FREE_PAGE_HINT)) {
 485                 names[VIRTIO_BALLOON_VQ_FREE_PAGE] = "free_page_vq";
 486                 callbacks[VIRTIO_BALLOON_VQ_FREE_PAGE] = NULL;
 487         }
 488
 489         err = vb->vdev->config->find_vqs(vb->vdev, VIRTIO_BALLOON_VQ_MAX,
 490                                          vqs, callbacks, names, NULL, NULL);
 491         if (err)
 492                 return err;
 493
 494         vb->inflate_vq = vqs[VIRTIO_BALLOON_VQ_INFLATE];
 495         vb->deflate_vq = vqs[VIRTIO_BALLOON_VQ_DEFLATE];
 496         if (virtio_has_feature(vb->vdev, VIRTIO_BALLOON_F_STATS_VQ)) {
 497                 struct scatterlist sg;
 498                 unsigned int num_stats;
 499                 vb->stats_vq = vqs[VIRTIO_BALLOON_VQ_STATS];
 500
 501                 /*
 502                  * Prime this virtqueue with one buffer so the hypervisor can
 503                  * use it to signal us later (it can't be broken yet!).
 504                  */
 505                 num_stats = update_balloon_stats(vb);
 506
 507                 sg_init_one(&sg, vb->stats, sizeof(vb->stats[0]) * num_stats);
 508                 err = virtqueue_add_outbuf(vb->stats_vq, &sg, 1, vb,
 509                                            GFP_KERNEL);
 510                 if (err) {
 511                         dev_warn(&vb->vdev->dev, "%s: add stat_vq failed\n",
 512                                  __func__);
 513                         return err;
 514                 }
 515                 virtqueue_kick(vb->stats_vq);
 516         }
 517
 518         if (virtio_has_feature(vb->vdev, VIRTIO_BALLOON_F_FREE_PAGE_HINT))
 519                 vb->free_page_vq = vqs[VIRTIO_BALLOON_VQ_FREE_PAGE];
 520
 521         return 0;
 522 }
 523
 524 static u32 virtio_balloon_cmd_id_received(struct virtio_balloon *vb)
 525 {
 526         if (test_and_clear_bit(VIRTIO_BALLOON_CONFIG_READ_CMD_ID,
 527                                &vb->config_read_bitmap))
 528                 virtio_cread(vb->vdev, struct virtio_balloon_config,
 529                              free_page_report_cmd_id,
 530                              &vb->cmd_id_received_cache);
 531
 532         return vb->cmd_id_received_cache;
 533 }
 534
 535 static int send_cmd_id_start(struct virtio_balloon *vb)
 536 {
 537         struct scatterlist sg;
 538         struct virtqueue *vq = vb->free_page_vq;
 539         int err, unused;
 540
 541         /* Detach all the used buffers from the vq */
 542         while (virtqueue_get_buf(vq, &unused))
 543                 ;
 544
 545         vb->cmd_id_active = virtio32_to_cpu(vb->vdev,
 546                                         virtio_balloon_cmd_id_received(vb));
 547         sg_init_one(&sg, &vb->cmd_id_active, sizeof(vb->cmd_id_active));
 548         err = virtqueue_add_outbuf(vq, &sg, 1, &vb->cmd_id_active, GFP_KERNEL);
 549         if (!err)
 550                 virtqueue_kick(vq);
 551         return err;
 552 }
 553
 554 static int send_cmd_id_stop(struct virtio_balloon *vb)
 555 {
 556         struct scatterlist sg;
 557         struct virtqueue *vq = vb->free_page_vq;
 558         int err, unused;
 559
 560         /* Detach all the used buffers from the vq */
 561         while (virtqueue_get_buf(vq, &unused))
 562                 ;
 563
 564         sg_init_one(&sg, &vb->cmd_id_stop, sizeof(vb->cmd_id_stop));
 565         err = virtqueue_add_outbuf(vq, &sg, 1, &vb->cmd_id_stop, GFP_KERNEL);
 566         if (!err)
 567                 virtqueue_kick(vq);
 568         return err;
 569 }
 570
 571 static int get_free_page_and_send(struct virtio_balloon *vb)
 572 {
 573         struct virtqueue *vq = vb->free_page_vq;
 574         struct page *page;
 575         struct scatterlist sg;
 576         int err, unused;
 577         void *p;
 578
 579         /* Detach all the used buffers from the vq */
 580         while (virtqueue_get_buf(vq, &unused))
 581                 ;
 582
 583         page = alloc_pages(VIRTIO_BALLOON_FREE_PAGE_ALLOC_FLAG,
 584                            VIRTIO_BALLOON_FREE_PAGE_ORDER);
 585         /*
 586          * When the allocation returns NULL, it indicates that we have got all
 587          * the possible free pages, so return -EINTR to stop.
 588          */
 589         if (!page)
 590                 return -EINTR;
 591
 592         p = page_address(page);
 593         sg_init_one(&sg, p, VIRTIO_BALLOON_FREE_PAGE_SIZE);
 594         /* There is always 1 entry reserved for the cmd id to use. */
 595         if (vq->num_free > 1) {
 596                 err = virtqueue_add_inbuf(vq, &sg, 1, p, GFP_KERNEL);
 597                 if (unlikely(err)) {
 598                         free_pages((unsigned long)p,
 599                                    VIRTIO_BALLOON_FREE_PAGE_ORDER);
 600                         return err;
 601                 }
 602                 virtqueue_kick(vq);
 603                 spin_lock_irq(&vb->free_page_list_lock);
 604                 balloon_page_push(&vb->free_page_list, page);
 605                 vb->num_free_page_blocks++;
 606                 spin_unlock_irq(&vb->free_page_list_lock);
 607         } else {
 608                 /*
 609                  * The vq has no available entry to add this page block, so
 610                  * just free it.
 611                  */
 612                 free_pages((unsigned long)p, VIRTIO_BALLOON_FREE_PAGE_ORDER);
 613         }
 614
 615         return 0;
 616 }
 617
 618 static int send_free_pages(struct virtio_balloon *vb)
 619 {
 620         int err;
 621         u32 cmd_id_active;
 622
 623         while (1) {
 624                 /*
 625                  * If a stop id or a new cmd id was just received from host,
 626                  * stop the reporting.
 627                  */
 628                 cmd_id_active = virtio32_to_cpu(vb->vdev, vb->cmd_id_active);
 629                 if (unlikely(cmd_id_active !=
 630                              virtio_balloon_cmd_id_received(vb)))
 631                         break;
 632
 633                 /*
 634                  * The free page blocks are allocated and sent to host one by
 635                  * one.
 636                  */
 637                 err = get_free_page_and_send(vb);
 638                 if (err == -EINTR)
 639                         break;
 640                 else if (unlikely(err))
 641                         return err;
 642         }
 643
 644         return 0;
 645 }
 646
 647 static void virtio_balloon_report_free_page(struct virtio_balloon *vb)
 648 {
 649         int err;
 650         struct device *dev = &vb->vdev->dev;
 651
 652         /* Start by sending the received cmd id to host with an outbuf. */
 653         err = send_cmd_id_start(vb);
 654         if (unlikely(err))
 655                 dev_err(dev, "Failed to send a start id, err = %d\n", err);
 656
 657         err = send_free_pages(vb);
 658         if (unlikely(err))
 659                 dev_err(dev, "Failed to send a free page, err = %d\n", err);
 660
 661         /* End by sending a stop id to host with an outbuf. */
 662         err = send_cmd_id_stop(vb);
 663         if (unlikely(err))
 664                 dev_err(dev, "Failed to send a stop id, err = %d\n", err);
 665 }
 666
 667 static void report_free_page_func(struct work_struct *work)
 668 {
 669         struct virtio_balloon *vb = container_of(work, struct virtio_balloon,
 670                                                  report_free_page_work);
 671         u32 cmd_id_received;
 672
 673         cmd_id_received = virtio_balloon_cmd_id_received(vb);
 674         if (cmd_id_received == VIRTIO_BALLOON_CMD_ID_DONE) {
 675                 /* Pass ULONG_MAX to give back all the free pages */
 676                 return_free_pages_to_mm(vb, ULONG_MAX);
 677         } else if (cmd_id_received != VIRTIO_BALLOON_CMD_ID_STOP &&
 678                    cmd_id_received !=
 679                    virtio32_to_cpu(vb->vdev, vb->cmd_id_active)) {
 680                 virtio_balloon_report_free_page(vb);
 681         }
 682 }
 683
 684 #ifdef CONFIG_BALLOON_COMPACTION
 685 /*
 686  * virtballoon_migratepage - perform the balloon page migration on behalf of
 687  *                           a compation thread.     (called under page lock)
 688  * @vb_dev_info: the balloon device
 689  * @newpage: page that will replace the isolated page after migration finishes.
 690  * @page   : the isolated (old) page that is about to be migrated to newpage.
 691  * @mode   : compaction mode -- not used for balloon page migration.
 692  *
 693  * After a ballooned page gets isolated by compaction procedures, this is the
 694  * function that performs the page migration on behalf of a compaction thread
 695  * The page migration for virtio balloon is done in a simple swap fashion which
 696  * follows these two macro steps:
 697  *  1) insert newpage into vb->pages list and update the host about it;
 698  *  2) update the host about the old page removed from vb->pages list;
 699  *
 700  * This function preforms the balloon page migration task.
 701  * Called through balloon_mapping->a_ops->migratepage
 702  */
 703 static int virtballoon_migratepage(struct balloon_dev_info *vb_dev_info,
 704                 struct page *newpage, struct page *page, enum migrate_mode mode)
 705 {
 706         struct virtio_balloon *vb = container_of(vb_dev_info,
 707                         struct virtio_balloon, vb_dev_info);
 708         unsigned long flags;
 709
 710         /*
 711          * In order to avoid lock contention while migrating pages concurrently
 712          * to leak_balloon() or fill_balloon() we just give up the balloon_lock
 713          * this turn, as it is easier to retry the page migration later.
 714          * This also prevents fill_balloon() getting stuck into a mutex
 715          * recursion in the case it ends up triggering memory compaction
 716          * while it is attempting to inflate the ballon.
 717          */
 718         if (!mutex_trylock(&vb->balloon_lock))
 719                 return -EAGAIN;
 720
 721         get_page(newpage); /* balloon reference */
 722
 723         /* balloon's page migration 1st step  -- inflate "newpage" */
 724         spin_lock_irqsave(&vb_dev_info->pages_lock, flags);
 725         balloon_page_insert(vb_dev_info, newpage);
 726         vb_dev_info->isolated_pages--;
 727         __count_vm_event(BALLOON_MIGRATE);
 728         spin_unlock_irqrestore(&vb_dev_info->pages_lock, flags);
 729         vb->num_pfns = VIRTIO_BALLOON_PAGES_PER_PAGE;
 730         set_page_pfns(vb, vb->pfns, newpage);
 731         tell_host(vb, vb->inflate_vq);
 732
 733         /* balloon's page migration 2nd step -- deflate "page" */
 734         spin_lock_irqsave(&vb_dev_info->pages_lock, flags);
 735         balloon_page_delete(page);
 736         spin_unlock_irqrestore(&vb_dev_info->pages_lock, flags);
 737         vb->num_pfns = VIRTIO_BALLOON_PAGES_PER_PAGE;
 738         set_page_pfns(vb, vb->pfns, page);
 739         tell_host(vb, vb->deflate_vq);
 740
 741         mutex_unlock(&vb->balloon_lock);
 742
 743         put_page(page); /* balloon reference */
 744
 745         return MIGRATEPAGE_SUCCESS;
 746 }
 747
 748 static struct dentry *balloon_mount(struct file_system_type *fs_type,
 749                 int flags, const char *dev_name, void *data)
 750 {
 751         static const struct dentry_operations ops = {
 752                 .d_dname = simple_dname,
 753         };
 754
 755         return mount_pseudo(fs_type, "balloon-kvm:", NULL, &ops,
 756                                 BALLOON_KVM_MAGIC);
 757 }
 758
 759 static struct file_system_type balloon_fs = {
 760         .name           = "balloon-kvm",
 761         .mount          = balloon_mount,
 762         .kill_sb        = kill_anon_super,
 763 };
 764
 765 #endif /* CONFIG_BALLOON_COMPACTION */
 766
 767 static unsigned long shrink_free_pages(struct virtio_balloon *vb,
 768                                        unsigned long pages_to_free)
 769 {
 770         unsigned long blocks_to_free, blocks_freed;
 771
 772         pages_to_free = round_up(pages_to_free,
 773                                  1 << VIRTIO_BALLOON_FREE_PAGE_ORDER);
 774         blocks_to_free = pages_to_free >> VIRTIO_BALLOON_FREE_PAGE_ORDER;
 775         blocks_freed = return_free_pages_to_mm(vb, blocks_to_free);
 776
 777         return blocks_freed << VIRTIO_BALLOON_FREE_PAGE_ORDER;
 778 }
 779
 780 static unsigned long shrink_balloon_pages(struct virtio_balloon *vb,
 781                                           unsigned long pages_to_free)
 782 {
 783         unsigned long pages_freed = 0;
 784
 785         /*
 786          * One invocation of leak_balloon can deflate at most
 787          * VIRTIO_BALLOON_ARRAY_PFNS_MAX balloon pages, so we call it
 788          * multiple times to deflate pages till reaching pages_to_free.
 789          */
 790         while (vb->num_pages && pages_to_free) {
 791                 pages_freed += leak_balloon(vb, pages_to_free) /
 792                                         VIRTIO_BALLOON_PAGES_PER_PAGE;
 793                 pages_to_free -= pages_freed;
 794         }
 795         update_balloon_size(vb);
 796
 797         return pages_freed;
 798 }
 799
 800 static unsigned long virtio_balloon_shrinker_scan(struct shrinker *shrinker,
 801                                                   struct shrink_control *sc)
 802 {
 803         unsigned long pages_to_free, pages_freed = 0;
 804         struct virtio_balloon *vb = container_of(shrinker,
 805                                         struct virtio_balloon, shrinker);
 806
 807         pages_to_free = sc->nr_to_scan * VIRTIO_BALLOON_PAGES_PER_PAGE;
 808
 809         if (virtio_has_feature(vb->vdev, VIRTIO_BALLOON_F_FREE_PAGE_HINT))
 810                 pages_freed = shrink_free_pages(vb, pages_to_free);
 811
 812         if (pages_freed >= pages_to_free)
 813                 return pages_freed;
 814
 815         pages_freed += shrink_balloon_pages(vb, pages_to_free - pages_freed);
 816
 817         return pages_freed;
 818 }
 819
 820 static unsigned long virtio_balloon_shrinker_count(struct shrinker *shrinker,
 821                                                    struct shrink_control *sc)
 822 {
 823         struct virtio_balloon *vb = container_of(shrinker,
 824                                         struct virtio_balloon, shrinker);
 825         unsigned long count;
 826
 827         count = vb->num_pages / VIRTIO_BALLOON_PAGES_PER_PAGE;
 828         count += vb->num_free_page_blocks >> VIRTIO_BALLOON_FREE_PAGE_ORDER;
 829
 830         return count;
 831 }
 832
 833 static void virtio_balloon_unregister_shrinker(struct virtio_balloon *vb)
 834 {
 835         unregister_shrinker(&vb->shrinker);
 836 }
 837
 838 static int virtio_balloon_register_shrinker(struct virtio_balloon *vb)
 839 {
 840         vb->shrinker.scan_objects = virtio_balloon_shrinker_scan;
 841         vb->shrinker.count_objects = virtio_balloon_shrinker_count;
 842         vb->shrinker.seeks = DEFAULT_SEEKS;
 843
 844         return register_shrinker(&vb->shrinker);
 845 }
 846
 847 static int virtballoon_probe(struct virtio_device *vdev)
 848 {
 849         struct virtio_balloon *vb;
 850         __u32 poison_val;
 851         int err;
 852
 853         if (!vdev->config->get) {
 854                 dev_err(&vdev->dev, "%s failure: config access disabled\n",
 855                         __func__);
 856                 return -EINVAL;
 857         }
 858
 859         vdev->priv = vb = kzalloc(sizeof(*vb), GFP_KERNEL);
 860         if (!vb) {
 861                 err = -ENOMEM;
 862                 goto out;
 863         }
 864
 865         INIT_WORK(&vb->update_balloon_stats_work, update_balloon_stats_func);
 866         INIT_WORK(&vb->update_balloon_size_work, update_balloon_size_func);
 867         spin_lock_init(&vb->stop_update_lock);
 868         mutex_init(&vb->balloon_lock);
 869         init_waitqueue_head(&vb->acked);
 870         vb->vdev = vdev;
 871
 872         balloon_devinfo_init(&vb->vb_dev_info);
 873
 874         err = init_vqs(vb);
 875         if (err)
 876                 goto out_free_vb;
 877
 878 #ifdef CONFIG_BALLOON_COMPACTION
 879         balloon_mnt = kern_mount(&balloon_fs);
 880         if (IS_ERR(balloon_mnt)) {
 881                 err = PTR_ERR(balloon_mnt);
 882                 goto out_del_vqs;
 883         }
 884
 885         vb->vb_dev_info.migratepage = virtballoon_migratepage;
 886         vb->vb_dev_info.inode = alloc_anon_inode(balloon_mnt->mnt_sb);
 887         if (IS_ERR(vb->vb_dev_info.inode)) {
 888                 err = PTR_ERR(vb->vb_dev_info.inode);
 889                 kern_unmount(balloon_mnt);
 890                 goto out_del_vqs;
 891         }
 892         vb->vb_dev_info.inode->i_mapping->a_ops = &balloon_aops;
 893 #endif
 894         if (virtio_has_feature(vdev, VIRTIO_BALLOON_F_FREE_PAGE_HINT)) {
 895                 /*
 896                  * There is always one entry reserved for cmd id, so the ring
 897                  * size needs to be at least two to report free page hints.
 898                  */
 899                 if (virtqueue_get_vring_size(vb->free_page_vq) < 2) {
 900                         err = -ENOSPC;
 901                         goto out_del_vqs;
 902                 }
 903                 vb->balloon_wq = alloc_workqueue("balloon-wq",
 904                                         WQ_FREEZABLE | WQ_CPU_INTENSIVE, 0);
 905                 if (!vb->balloon_wq) {
 906                         err = -ENOMEM;
 907                         goto out_del_vqs;
 908                 }
 909                 INIT_WORK(&vb->report_free_page_work, report_free_page_func);
 910                 vb->cmd_id_received_cache = VIRTIO_BALLOON_CMD_ID_STOP;
 911                 vb->cmd_id_active = cpu_to_virtio32(vb->vdev,
 912                                                   VIRTIO_BALLOON_CMD_ID_STOP);
 913                 vb->cmd_id_stop = cpu_to_virtio32(vb->vdev,
 914                                                   VIRTIO_BALLOON_CMD_ID_STOP);
 915                 spin_lock_init(&vb->free_page_list_lock);
 916                 INIT_LIST_HEAD(&vb->free_page_list);
 917                 if (virtio_has_feature(vdev, VIRTIO_BALLOON_F_PAGE_POISON)) {
 918                         memset(&poison_val, PAGE_POISON, sizeof(poison_val));
 919                         virtio_cwrite(vb->vdev, struct virtio_balloon_config,
 920                                       poison_val, &poison_val);
 921                 }
 922         }
 923         /*
 924          * We continue to use VIRTIO_BALLOON_F_DEFLATE_ON_OOM to decide if a
 925          * shrinker needs to be registered to relieve memory pressure.
 926          */
 927         if (virtio_has_feature(vb->vdev, VIRTIO_BALLOON_F_DEFLATE_ON_OOM)) {
 928                 err = virtio_balloon_register_shrinker(vb);
 929                 if (err)
 930                         goto out_del_balloon_wq;
 931         }
 932         virtio_device_ready(vdev);
 933
 934         if (towards_target(vb))
 935                 virtballoon_changed(vdev);
 936         return 0;
 937
 938 out_del_balloon_wq:
 939         if (virtio_has_feature(vdev, VIRTIO_BALLOON_F_FREE_PAGE_HINT))
 940                 destroy_workqueue(vb->balloon_wq);
 941 out_del_vqs:
 942         vdev->config->del_vqs(vdev);
 943 out_free_vb:
 944         kfree(vb);
 945 out:
 946         return err;
 947 }
 948
 949 static void remove_common(struct virtio_balloon *vb)
 950 {
 951         /* There might be pages left in the balloon: free them. */
 952         while (vb->num_pages)
 953                 leak_balloon(vb, vb->num_pages);
 954         update_balloon_size(vb);
 955
 956         /* Now we reset the device so we can clean up the queues. */
 957         vb->vdev->config->reset(vb->vdev);
 958
 959         vb->vdev->config->del_vqs(vb->vdev);
 960 }
 961
 962 static void virtballoon_remove(struct virtio_device *vdev)
 963 {
 964         struct virtio_balloon *vb = vdev->priv;
 965
 966         if (virtio_has_feature(vb->vdev, VIRTIO_BALLOON_F_DEFLATE_ON_OOM))
 967                 virtio_balloon_unregister_shrinker(vb);
 968         spin_lock_irq(&vb->stop_update_lock);
 969         vb->stop_update = true;
 970         spin_unlock_irq(&vb->stop_update_lock);
 971         cancel_work_sync(&vb->update_balloon_size_work);
 972         cancel_work_sync(&vb->update_balloon_stats_work);
 973
 974         if (virtio_has_feature(vdev, VIRTIO_BALLOON_F_FREE_PAGE_HINT)) {
 975                 cancel_work_sync(&vb->report_free_page_work);
 976                 destroy_workqueue(vb->balloon_wq);
 977         }
 978
 979         remove_common(vb);
 980 #ifdef CONFIG_BALLOON_COMPACTION
 981         if (vb->vb_dev_info.inode)
 982                 iput(vb->vb_dev_info.inode);
 983
 984         kern_unmount(balloon_mnt);
 985 #endif
 986         kfree(vb);
 987 }
 988
 989 #ifdef CONFIG_PM_SLEEP
 990 static int virtballoon_freeze(struct virtio_device *vdev)
 991 {
 992         struct virtio_balloon *vb = vdev->priv;
 993
 994         /*
 995          * The workqueue is already frozen by the PM core before this
 996          * function is called.
 997          */
 998         remove_common(vb);
 999         return 0;
1000 }
1001
1002 static int virtballoon_restore(struct virtio_device *vdev)
1003 {
1004         struct virtio_balloon *vb = vdev->priv;
1005         int ret;
1006
1007         ret = init_vqs(vdev->priv);
1008         if (ret)
1009                 return ret;
1010
1011         virtio_device_ready(vdev);
1012
1013         if (towards_target(vb))
1014                 virtballoon_changed(vdev);
1015         update_balloon_size(vb);
1016         return 0;
1017 }
1018 #endif
1019
1020 static int virtballoon_validate(struct virtio_device *vdev)
1021 {
1022         if (!page_poisoning_enabled())
1023                 __virtio_clear_bit(vdev, VIRTIO_BALLOON_F_PAGE_POISON);
1024
1025         __virtio_clear_bit(vdev, VIRTIO_F_IOMMU_PLATFORM);
1026         return 0;
1027 }
1028
1029 static unsigned int features[] = {
1030         VIRTIO_BALLOON_F_MUST_TELL_HOST,
1031         VIRTIO_BALLOON_F_STATS_VQ,
1032         VIRTIO_BALLOON_F_DEFLATE_ON_OOM,
1033         VIRTIO_BALLOON_F_FREE_PAGE_HINT,
1034         VIRTIO_BALLOON_F_PAGE_POISON,
1035 };
1036
1037 static struct virtio_driver virtio_balloon_driver = {
1038         .feature_table = features,
1039         .feature_table_size = ARRAY_SIZE(features),
1040         .driver.name =  KBUILD_MODNAME,
1041         .driver.owner = THIS_MODULE,
1042         .id_table =     id_table,
1043         .validate =     virtballoon_validate,
1044         .probe =        virtballoon_probe,
1045         .remove =       virtballoon_remove,
1046         .config_changed = virtballoon_changed,
1047 #ifdef CONFIG_PM_SLEEP
1048         .freeze =       virtballoon_freeze,
1049         .restore =      virtballoon_restore,
1050 #endif
1051 };
1052
1053 module_virtio_driver(virtio_balloon_driver);
1054 MODULE_DEVICE_TABLE(virtio, id_table);
1055 MODULE_DESCRIPTION("Virtio balloon driver");
1056 MODULE_LICENSE("GPL");