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 #include <linux/pseudo_fs.h>
  22
  23 /*
  24  * Balloon device works in 4K page units.  So each page is pointed to by
  25  * multiple balloon pages.  All memory counters in this driver are in balloon
  26  * page units.
  27  */
  28 #define VIRTIO_BALLOON_PAGES_PER_PAGE (unsigned)(PAGE_SIZE >> VIRTIO_BALLOON_PFN_SHIFT)
  29 #define VIRTIO_BALLOON_ARRAY_PFNS_MAX 256
  30 #define VIRTBALLOON_OOM_NOTIFY_PRIORITY 80
  31
  32 #define VIRTIO_BALLOON_FREE_PAGE_ALLOC_FLAG (__GFP_NORETRY | __GFP_NOWARN | \
  33                                              __GFP_NOMEMALLOC)
  34 /* The order of free page blocks to report to host */
  35 #define VIRTIO_BALLOON_FREE_PAGE_ORDER (MAX_ORDER - 1)
  36 /* The size of a free page block in bytes */
  37 #define VIRTIO_BALLOON_FREE_PAGE_SIZE \
  38         (1 << (VIRTIO_BALLOON_FREE_PAGE_ORDER + PAGE_SHIFT))
  39
  40 #ifdef CONFIG_BALLOON_COMPACTION
  41 static struct vfsmount *balloon_mnt;
  42 #endif
  43
  44 enum virtio_balloon_vq {
  45         VIRTIO_BALLOON_VQ_INFLATE,
  46         VIRTIO_BALLOON_VQ_DEFLATE,
  47         VIRTIO_BALLOON_VQ_STATS,
  48         VIRTIO_BALLOON_VQ_FREE_PAGE,
  49         VIRTIO_BALLOON_VQ_MAX
  50 };
  51
  52 enum virtio_balloon_config_read {
  53         VIRTIO_BALLOON_CONFIG_READ_CMD_ID = 0,
  54 };
  55
  56 struct virtio_balloon {
  57         struct virtio_device *vdev;
  58         struct virtqueue *inflate_vq, *deflate_vq, *stats_vq, *free_page_vq;
  59
  60         /* Balloon's own wq for cpu-intensive work items */
  61         struct workqueue_struct *balloon_wq;
  62         /* The free page reporting work item submitted to the balloon wq */
  63         struct work_struct report_free_page_work;
  64
  65         /* The balloon servicing is delegated to a freezable workqueue. */
  66         struct work_struct update_balloon_stats_work;
  67         struct work_struct update_balloon_size_work;
  68
  69         /* Prevent updating balloon when it is being canceled. */
  70         spinlock_t stop_update_lock;
  71         bool stop_update;
  72         /* Bitmap to indicate if reading the related config fields are needed */
  73         unsigned long config_read_bitmap;
  74
  75         /* The list of allocated free pages, waiting to be given back to mm */
  76         struct list_head free_page_list;
  77         spinlock_t free_page_list_lock;
  78         /* The number of free page blocks on the above list */
  79         unsigned long num_free_page_blocks;
  80         /*
  81          * The cmd id received from host.
  82          * Read it via virtio_balloon_cmd_id_received to get the latest value
  83          * sent from host.
  84          */
  85         u32 cmd_id_received_cache;
  86         /* The cmd id that is actively in use */
  87         __virtio32 cmd_id_active;
  88         /* Buffer to store the stop sign */
  89         __virtio32 cmd_id_stop;
  90
  91         /* Waiting for host to ack the pages we released. */
  92         wait_queue_head_t acked;
  93
  94         /* Number of balloon pages we've told the Host we're not using. */
  95         unsigned int num_pages;
  96         /*
  97          * The pages we've told the Host we're not using are enqueued
  98          * at vb_dev_info->pages list.
  99          * Each page on this list adds VIRTIO_BALLOON_PAGES_PER_PAGE
 100          * to num_pages above.
 101          */
 102         struct balloon_dev_info vb_dev_info;
 103
 104         /* Synchronize access/update to this struct virtio_balloon elements */
 105         struct mutex balloon_lock;
 106
 107         /* The array of pfns we tell the Host about. */
 108         unsigned int num_pfns;
 109         __virtio32 pfns[VIRTIO_BALLOON_ARRAY_PFNS_MAX];
 110
 111         /* Memory statistics */
 112         struct virtio_balloon_stat stats[VIRTIO_BALLOON_S_NR];
 113
 114         /* To register a shrinker to shrink memory upon memory pressure */
 115         struct shrinker shrinker;
 116 };
 117
 118 static struct virtio_device_id id_table[] = {
 119         { VIRTIO_ID_BALLOON, VIRTIO_DEV_ANY_ID },
 120         { 0 },
 121 };
 122
 123 static u32 page_to_balloon_pfn(struct page *page)
 124 {
 125         unsigned long pfn = page_to_pfn(page);
 126
 127         BUILD_BUG_ON(PAGE_SHIFT < VIRTIO_BALLOON_PFN_SHIFT);
 128         /* Convert pfn from Linux page size to balloon page size. */
 129         return pfn * VIRTIO_BALLOON_PAGES_PER_PAGE;
 130 }
 131
 132 static void balloon_ack(struct virtqueue *vq)
 133 {
 134         struct virtio_balloon *vb = vq->vdev->priv;
 135
 136         wake_up(&vb->acked);
 137 }
 138
 139 static void tell_host(struct virtio_balloon *vb, struct virtqueue *vq)
 140 {
 141         struct scatterlist sg;
 142         unsigned int len;
 143
 144         sg_init_one(&sg, vb->pfns, sizeof(vb->pfns[0]) * vb->num_pfns);
 145
 146         /* We should always be able to add one buffer to an empty queue. */
 147         virtqueue_add_outbuf(vq, &sg, 1, vb, GFP_KERNEL);
 148         virtqueue_kick(vq);
 149
 150         /* When host has read buffer, this completes via balloon_ack */
 151         wait_event(vb->acked, virtqueue_get_buf(vq, &len));
 152
 153 }
 154
 155 static void set_page_pfns(struct virtio_balloon *vb,
 156                           __virtio32 pfns[], struct page *page)
 157 {
 158         unsigned int i;
 159
 160         /*
 161          * Set balloon pfns pointing at this page.
 162          * Note that the first pfn points at start of the page.
 163          */
 164         for (i = 0; i < VIRTIO_BALLOON_PAGES_PER_PAGE; i++)
 165                 pfns[i] = cpu_to_virtio32(vb->vdev,
 166                                           page_to_balloon_pfn(page) + i);
 167 }
 168
 169 static unsigned fill_balloon(struct virtio_balloon *vb, size_t num)
 170 {
 171         unsigned num_allocated_pages;
 172         unsigned num_pfns;
 173         struct page *page;
 174         LIST_HEAD(pages);
 175
 176         /* We can only do one array worth at a time. */
 177         num = min(num, ARRAY_SIZE(vb->pfns));
 178
 179         for (num_pfns = 0; num_pfns < num;
 180              num_pfns += VIRTIO_BALLOON_PAGES_PER_PAGE) {
 181                 struct page *page = balloon_page_alloc();
 182
 183                 if (!page) {
 184                         dev_info_ratelimited(&vb->vdev->dev,
 185                                              "Out of puff! Can't get %u pages\n",
 186                                              VIRTIO_BALLOON_PAGES_PER_PAGE);
 187                         /* Sleep for at least 1/5 of a second before retry. */
 188                         msleep(200);
 189                         break;
 190                 }
 191
 192                 balloon_page_push(&pages, page);
 193         }
 194
 195         mutex_lock(&vb->balloon_lock);
 196
 197         vb->num_pfns = 0;
 198
 199         while ((page = balloon_page_pop(&pages))) {
 200                 balloon_page_enqueue(&vb->vb_dev_info, page);
 201
 202                 set_page_pfns(vb, vb->pfns + vb->num_pfns, page);
 203                 vb->num_pages += VIRTIO_BALLOON_PAGES_PER_PAGE;
 204                 if (!virtio_has_feature(vb->vdev,
 205                                         VIRTIO_BALLOON_F_DEFLATE_ON_OOM))
 206                         adjust_managed_page_count(page, -1);
 207                 vb->num_pfns += VIRTIO_BALLOON_PAGES_PER_PAGE;
 208         }
 209
 210         num_allocated_pages = vb->num_pfns;
 211         /* Did we get any? */
 212         if (vb->num_pfns != 0)
 213                 tell_host(vb, vb->inflate_vq);
 214         mutex_unlock(&vb->balloon_lock);
 215
 216         return num_allocated_pages;
 217 }
 218
 219 static void release_pages_balloon(struct virtio_balloon *vb,
 220                                  struct list_head *pages)
 221 {
 222         struct page *page, *next;
 223
 224         list_for_each_entry_safe(page, next, pages, lru) {
 225                 if (!virtio_has_feature(vb->vdev,
 226                                         VIRTIO_BALLOON_F_DEFLATE_ON_OOM))
 227                         adjust_managed_page_count(page, 1);
 228                 list_del(&page->lru);
 229                 put_page(page); /* balloon reference */
 230         }
 231 }
 232
 233 static unsigned leak_balloon(struct virtio_balloon *vb, size_t num)
 234 {
 235         unsigned num_freed_pages;
 236         struct page *page;
 237         struct balloon_dev_info *vb_dev_info = &vb->vb_dev_info;
 238         LIST_HEAD(pages);
 239
 240         /* We can only do one array worth at a time. */
 241         num = min(num, ARRAY_SIZE(vb->pfns));
 242
 243         mutex_lock(&vb->balloon_lock);
 244         /* We can't release more pages than taken */
 245         num = min(num, (size_t)vb->num_pages);
 246         for (vb->num_pfns = 0; vb->num_pfns < num;
 247              vb->num_pfns += VIRTIO_BALLOON_PAGES_PER_PAGE) {
 248                 page = balloon_page_dequeue(vb_dev_info);
 249                 if (!page)
 250                         break;
 251                 set_page_pfns(vb, vb->pfns + vb->num_pfns, page);
 252                 list_add(&page->lru, &pages);
 253                 vb->num_pages -= VIRTIO_BALLOON_PAGES_PER_PAGE;
 254         }
 255
 256         num_freed_pages = vb->num_pfns;
 257         /*
 258          * Note that if
 259          * virtio_has_feature(vdev, VIRTIO_BALLOON_F_MUST_TELL_HOST);
 260          * is true, we *have* to do it in this order
 261          */
 262         if (vb->num_pfns != 0)
 263                 tell_host(vb, vb->deflate_vq);
 264         release_pages_balloon(vb, &pages);
 265         mutex_unlock(&vb->balloon_lock);
 266         return num_freed_pages;
 267 }
 268
 269 static inline void update_stat(struct virtio_balloon *vb, int idx,
 270                                u16 tag, u64 val)
 271 {
 272         BUG_ON(idx >= VIRTIO_BALLOON_S_NR);
 273         vb->stats[idx].tag = cpu_to_virtio16(vb->vdev, tag);
 274         vb->stats[idx].val = cpu_to_virtio64(vb->vdev, val);
 275 }
 276
 277 #define pages_to_bytes(x) ((u64)(x) << PAGE_SHIFT)
 278
 279 static unsigned int update_balloon_stats(struct virtio_balloon *vb)
 280 {
 281         unsigned long events[NR_VM_EVENT_ITEMS];
 282         struct sysinfo i;
 283         unsigned int idx = 0;
 284         long available;
 285         unsigned long caches;
 286
 287         all_vm_events(events);
 288         si_meminfo(&i);
 289
 290         available = si_mem_available();
 291         caches = global_node_page_state(NR_FILE_PAGES);
 292
 293 #ifdef CONFIG_VM_EVENT_COUNTERS
 294         update_stat(vb, idx++, VIRTIO_BALLOON_S_SWAP_IN,
 295                                 pages_to_bytes(events[PSWPIN]));
 296         update_stat(vb, idx++, VIRTIO_BALLOON_S_SWAP_OUT,
 297                                 pages_to_bytes(events[PSWPOUT]));
 298         update_stat(vb, idx++, VIRTIO_BALLOON_S_MAJFLT, events[PGMAJFAULT]);
 299         update_stat(vb, idx++, VIRTIO_BALLOON_S_MINFLT, events[PGFAULT]);
 300 #ifdef CONFIG_HUGETLB_PAGE
 301         update_stat(vb, idx++, VIRTIO_BALLOON_S_HTLB_PGALLOC,
 302                     events[HTLB_BUDDY_PGALLOC]);
 303         update_stat(vb, idx++, VIRTIO_BALLOON_S_HTLB_PGFAIL,
 304                     events[HTLB_BUDDY_PGALLOC_FAIL]);
 305 #endif
 306 #endif
 307         update_stat(vb, idx++, VIRTIO_BALLOON_S_MEMFREE,
 308                                 pages_to_bytes(i.freeram));
 309         update_stat(vb, idx++, VIRTIO_BALLOON_S_MEMTOT,
 310                                 pages_to_bytes(i.totalram));
 311         update_stat(vb, idx++, VIRTIO_BALLOON_S_AVAIL,
 312                                 pages_to_bytes(available));
 313         update_stat(vb, idx++, VIRTIO_BALLOON_S_CACHES,
 314                                 pages_to_bytes(caches));
 315
 316         return idx;
 317 }
 318
 319 /*
 320  * While most virtqueues communicate guest-initiated requests to the hypervisor,
 321  * the stats queue operates in reverse.  The driver initializes the virtqueue
 322  * with a single buffer.  From that point forward, all conversations consist of
 323  * a hypervisor request (a call to this function) which directs us to refill
 324  * the virtqueue with a fresh stats buffer.  Since stats collection can sleep,
 325  * we delegate the job to a freezable workqueue that will do the actual work via
 326  * stats_handle_request().
 327  */
 328 static void stats_request(struct virtqueue *vq)
 329 {
 330         struct virtio_balloon *vb = vq->vdev->priv;
 331
 332         spin_lock(&vb->stop_update_lock);
 333         if (!vb->stop_update)
 334                 queue_work(system_freezable_wq, &vb->update_balloon_stats_work);
 335         spin_unlock(&vb->stop_update_lock);
 336 }
 337
 338 static void stats_handle_request(struct virtio_balloon *vb)
 339 {
 340         struct virtqueue *vq;
 341         struct scatterlist sg;
 342         unsigned int len, num_stats;
 343
 344         num_stats = update_balloon_stats(vb);
 345
 346         vq = vb->stats_vq;
 347         if (!virtqueue_get_buf(vq, &len))
 348                 return;
 349         sg_init_one(&sg, vb->stats, sizeof(vb->stats[0]) * num_stats);
 350         virtqueue_add_outbuf(vq, &sg, 1, vb, GFP_KERNEL);
 351         virtqueue_kick(vq);
 352 }
 353
 354 static inline s64 towards_target(struct virtio_balloon *vb)
 355 {
 356         s64 target;
 357         u32 num_pages;
 358
 359         virtio_cread(vb->vdev, struct virtio_balloon_config, num_pages,
 360                      &num_pages);
 361
 362         /* Legacy balloon config space is LE, unlike all other devices. */
 363         if (!virtio_has_feature(vb->vdev, VIRTIO_F_VERSION_1))
 364                 num_pages = le32_to_cpu((__force __le32)num_pages);
 365
 366         target = num_pages;
 367         return target - vb->num_pages;
 368 }
 369
 370 /* Gives back @num_to_return blocks of free pages to mm. */
 371 static unsigned long return_free_pages_to_mm(struct virtio_balloon *vb,
 372                                              unsigned long num_to_return)
 373 {
 374         struct page *page;
 375         unsigned long num_returned;
 376
 377         spin_lock_irq(&vb->free_page_list_lock);
 378         for (num_returned = 0; num_returned < num_to_return; num_returned++) {
 379                 page = balloon_page_pop(&vb->free_page_list);
 380                 if (!page)
 381                         break;
 382                 free_pages((unsigned long)page_address(page),
 383                            VIRTIO_BALLOON_FREE_PAGE_ORDER);
 384         }
 385         vb->num_free_page_blocks -= num_returned;
 386         spin_unlock_irq(&vb->free_page_list_lock);
 387
 388         return num_returned;
 389 }
 390
 391 static void virtio_balloon_queue_free_page_work(struct virtio_balloon *vb)
 392 {
 393         if (!virtio_has_feature(vb->vdev, VIRTIO_BALLOON_F_FREE_PAGE_HINT))
 394                 return;
 395
 396         /* No need to queue the work if the bit was already set. */
 397         if (test_and_set_bit(VIRTIO_BALLOON_CONFIG_READ_CMD_ID,
 398                              &vb->config_read_bitmap))
 399                 return;
 400
 401         queue_work(vb->balloon_wq, &vb->report_free_page_work);
 402 }
 403
 404 static void virtballoon_changed(struct virtio_device *vdev)
 405 {
 406         struct virtio_balloon *vb = vdev->priv;
 407         unsigned long flags;
 408
 409         spin_lock_irqsave(&vb->stop_update_lock, flags);
 410         if (!vb->stop_update) {
 411                 queue_work(system_freezable_wq,
 412                            &vb->update_balloon_size_work);
 413                 virtio_balloon_queue_free_page_work(vb);
 414         }
 415         spin_unlock_irqrestore(&vb->stop_update_lock, flags);
 416 }
 417
 418 static void update_balloon_size(struct virtio_balloon *vb)
 419 {
 420         u32 actual = vb->num_pages;
 421
 422         /* Legacy balloon config space is LE, unlike all other devices. */
 423         if (!virtio_has_feature(vb->vdev, VIRTIO_F_VERSION_1))
 424                 actual = (__force u32)cpu_to_le32(actual);
 425
 426         virtio_cwrite(vb->vdev, struct virtio_balloon_config, actual,
 427                       &actual);
 428 }
 429
 430 static void update_balloon_stats_func(struct work_struct *work)
 431 {
 432         struct virtio_balloon *vb;
 433
 434         vb = container_of(work, struct virtio_balloon,
 435                           update_balloon_stats_work);
 436         stats_handle_request(vb);
 437 }
 438
 439 static void update_balloon_size_func(struct work_struct *work)
 440 {
 441         struct virtio_balloon *vb;
 442         s64 diff;
 443
 444         vb = container_of(work, struct virtio_balloon,
 445                           update_balloon_size_work);
 446         diff = towards_target(vb);
 447
 448         if (!diff)
 449                 return;
 450
 451         if (diff > 0)
 452                 diff -= fill_balloon(vb, diff);
 453         else
 454                 diff += leak_balloon(vb, -diff);
 455         update_balloon_size(vb);
 456
 457         if (diff)
 458                 queue_work(system_freezable_wq, work);
 459 }
 460
 461 static int init_vqs(struct virtio_balloon *vb)
 462 {
 463         struct virtqueue *vqs[VIRTIO_BALLOON_VQ_MAX];
 464         vq_callback_t *callbacks[VIRTIO_BALLOON_VQ_MAX];
 465         const char *names[VIRTIO_BALLOON_VQ_MAX];
 466         int err;
 467
 468         /*
 469          * Inflateq and deflateq are used unconditionally. The names[]
 470          * will be NULL if the related feature is not enabled, which will
 471          * cause no allocation for the corresponding virtqueue in find_vqs.
 472          */
 473         callbacks[VIRTIO_BALLOON_VQ_INFLATE] = balloon_ack;
 474         names[VIRTIO_BALLOON_VQ_INFLATE] = "inflate";
 475         callbacks[VIRTIO_BALLOON_VQ_DEFLATE] = balloon_ack;
 476         names[VIRTIO_BALLOON_VQ_DEFLATE] = "deflate";
 477         names[VIRTIO_BALLOON_VQ_STATS] = NULL;
 478         names[VIRTIO_BALLOON_VQ_FREE_PAGE] = NULL;
 479
 480         if (virtio_has_feature(vb->vdev, VIRTIO_BALLOON_F_STATS_VQ)) {
 481                 names[VIRTIO_BALLOON_VQ_STATS] = "stats";
 482                 callbacks[VIRTIO_BALLOON_VQ_STATS] = stats_request;
 483         }
 484
 485         if (virtio_has_feature(vb->vdev, VIRTIO_BALLOON_F_FREE_PAGE_HINT)) {
 486                 names[VIRTIO_BALLOON_VQ_FREE_PAGE] = "free_page_vq";
 487                 callbacks[VIRTIO_BALLOON_VQ_FREE_PAGE] = NULL;
 488         }
 489
 490         err = vb->vdev->config->find_vqs(vb->vdev, VIRTIO_BALLOON_VQ_MAX,
 491                                          vqs, callbacks, names, NULL, NULL);
 492         if (err)
 493                 return err;
 494
 495         vb->inflate_vq = vqs[VIRTIO_BALLOON_VQ_INFLATE];
 496         vb->deflate_vq = vqs[VIRTIO_BALLOON_VQ_DEFLATE];
 497         if (virtio_has_feature(vb->vdev, VIRTIO_BALLOON_F_STATS_VQ)) {
 498                 struct scatterlist sg;
 499                 unsigned int num_stats;
 500                 vb->stats_vq = vqs[VIRTIO_BALLOON_VQ_STATS];
 501
 502                 /*
 503                  * Prime this virtqueue with one buffer so the hypervisor can
 504                  * use it to signal us later (it can't be broken yet!).
 505                  */
 506                 num_stats = update_balloon_stats(vb);
 507
 508                 sg_init_one(&sg, vb->stats, sizeof(vb->stats[0]) * num_stats);
 509                 err = virtqueue_add_outbuf(vb->stats_vq, &sg, 1, vb,
 510                                            GFP_KERNEL);
 511                 if (err) {
 512                         dev_warn(&vb->vdev->dev, "%s: add stat_vq failed\n",
 513                                  __func__);
 514                         return err;
 515                 }
 516                 virtqueue_kick(vb->stats_vq);
 517         }
 518
 519         if (virtio_has_feature(vb->vdev, VIRTIO_BALLOON_F_FREE_PAGE_HINT))
 520                 vb->free_page_vq = vqs[VIRTIO_BALLOON_VQ_FREE_PAGE];
 521
 522         return 0;
 523 }
 524
 525 static u32 virtio_balloon_cmd_id_received(struct virtio_balloon *vb)
 526 {
 527         if (test_and_clear_bit(VIRTIO_BALLOON_CONFIG_READ_CMD_ID,
 528                                &vb->config_read_bitmap))
 529                 virtio_cread(vb->vdev, struct virtio_balloon_config,
 530                              free_page_report_cmd_id,
 531                              &vb->cmd_id_received_cache);
 532
 533         return vb->cmd_id_received_cache;
 534 }
 535
 536 static int send_cmd_id_start(struct virtio_balloon *vb)
 537 {
 538         struct scatterlist sg;
 539         struct virtqueue *vq = vb->free_page_vq;
 540         int err, unused;
 541
 542         /* Detach all the used buffers from the vq */
 543         while (virtqueue_get_buf(vq, &unused))
 544                 ;
 545
 546         vb->cmd_id_active = virtio32_to_cpu(vb->vdev,
 547                                         virtio_balloon_cmd_id_received(vb));
 548         sg_init_one(&sg, &vb->cmd_id_active, sizeof(vb->cmd_id_active));
 549         err = virtqueue_add_outbuf(vq, &sg, 1, &vb->cmd_id_active, GFP_KERNEL);
 550         if (!err)
 551                 virtqueue_kick(vq);
 552         return err;
 553 }
 554
 555 static int send_cmd_id_stop(struct virtio_balloon *vb)
 556 {
 557         struct scatterlist sg;
 558         struct virtqueue *vq = vb->free_page_vq;
 559         int err, unused;
 560
 561         /* Detach all the used buffers from the vq */
 562         while (virtqueue_get_buf(vq, &unused))
 563                 ;
 564
 565         sg_init_one(&sg, &vb->cmd_id_stop, sizeof(vb->cmd_id_stop));
 566         err = virtqueue_add_outbuf(vq, &sg, 1, &vb->cmd_id_stop, GFP_KERNEL);
 567         if (!err)
 568                 virtqueue_kick(vq);
 569         return err;
 570 }
 571
 572 static int get_free_page_and_send(struct virtio_balloon *vb)
 573 {
 574         struct virtqueue *vq = vb->free_page_vq;
 575         struct page *page;
 576         struct scatterlist sg;
 577         int err, unused;
 578         void *p;
 579
 580         /* Detach all the used buffers from the vq */
 581         while (virtqueue_get_buf(vq, &unused))
 582                 ;
 583
 584         page = alloc_pages(VIRTIO_BALLOON_FREE_PAGE_ALLOC_FLAG,
 585                            VIRTIO_BALLOON_FREE_PAGE_ORDER);
 586         /*
 587          * When the allocation returns NULL, it indicates that we have got all
 588          * the possible free pages, so return -EINTR to stop.
 589          */
 590         if (!page)
 591                 return -EINTR;
 592
 593         p = page_address(page);
 594         sg_init_one(&sg, p, VIRTIO_BALLOON_FREE_PAGE_SIZE);
 595         /* There is always 1 entry reserved for the cmd id to use. */
 596         if (vq->num_free > 1) {
 597                 err = virtqueue_add_inbuf(vq, &sg, 1, p, GFP_KERNEL);
 598                 if (unlikely(err)) {
 599                         free_pages((unsigned long)p,
 600                                    VIRTIO_BALLOON_FREE_PAGE_ORDER);
 601                         return err;
 602                 }
 603                 virtqueue_kick(vq);
 604                 spin_lock_irq(&vb->free_page_list_lock);
 605                 balloon_page_push(&vb->free_page_list, page);
 606                 vb->num_free_page_blocks++;
 607                 spin_unlock_irq(&vb->free_page_list_lock);
 608         } else {
 609                 /*
 610                  * The vq has no available entry to add this page block, so
 611                  * just free it.
 612                  */
 613                 free_pages((unsigned long)p, VIRTIO_BALLOON_FREE_PAGE_ORDER);
 614         }
 615
 616         return 0;
 617 }
 618
 619 static int send_free_pages(struct virtio_balloon *vb)
 620 {
 621         int err;
 622         u32 cmd_id_active;
 623
 624         while (1) {
 625                 /*
 626                  * If a stop id or a new cmd id was just received from host,
 627                  * stop the reporting.
 628                  */
 629                 cmd_id_active = virtio32_to_cpu(vb->vdev, vb->cmd_id_active);
 630                 if (unlikely(cmd_id_active !=
 631                              virtio_balloon_cmd_id_received(vb)))
 632                         break;
 633
 634                 /*
 635                  * The free page blocks are allocated and sent to host one by
 636                  * one.
 637                  */
 638                 err = get_free_page_and_send(vb);
 639                 if (err == -EINTR)
 640                         break;
 641                 else if (unlikely(err))
 642                         return err;
 643         }
 644
 645         return 0;
 646 }
 647
 648 static void virtio_balloon_report_free_page(struct virtio_balloon *vb)
 649 {
 650         int err;
 651         struct device *dev = &vb->vdev->dev;
 652
 653         /* Start by sending the received cmd id to host with an outbuf. */
 654         err = send_cmd_id_start(vb);
 655         if (unlikely(err))
 656                 dev_err(dev, "Failed to send a start id, err = %d\n", err);
 657
 658         err = send_free_pages(vb);
 659         if (unlikely(err))
 660                 dev_err(dev, "Failed to send a free page, err = %d\n", err);
 661
 662         /* End by sending a stop id to host with an outbuf. */
 663         err = send_cmd_id_stop(vb);
 664         if (unlikely(err))
 665                 dev_err(dev, "Failed to send a stop id, err = %d\n", err);
 666 }
 667
 668 static void report_free_page_func(struct work_struct *work)
 669 {
 670         struct virtio_balloon *vb = container_of(work, struct virtio_balloon,
 671                                                  report_free_page_work);
 672         u32 cmd_id_received;
 673
 674         cmd_id_received = virtio_balloon_cmd_id_received(vb);
 675         if (cmd_id_received == VIRTIO_BALLOON_CMD_ID_DONE) {
 676                 /* Pass ULONG_MAX to give back all the free pages */
 677                 return_free_pages_to_mm(vb, ULONG_MAX);
 678         } else if (cmd_id_received != VIRTIO_BALLOON_CMD_ID_STOP &&
 679                    cmd_id_received !=
 680                    virtio32_to_cpu(vb->vdev, vb->cmd_id_active)) {
 681                 virtio_balloon_report_free_page(vb);
 682         }
 683 }
 684
 685 #ifdef CONFIG_BALLOON_COMPACTION
 686 /*
 687  * virtballoon_migratepage - perform the balloon page migration on behalf of
 688  *                           a compation thread.     (called under page lock)
 689  * @vb_dev_info: the balloon device
 690  * @newpage: page that will replace the isolated page after migration finishes.
 691  * @page   : the isolated (old) page that is about to be migrated to newpage.
 692  * @mode   : compaction mode -- not used for balloon page migration.
 693  *
 694  * After a ballooned page gets isolated by compaction procedures, this is the
 695  * function that performs the page migration on behalf of a compaction thread
 696  * The page migration for virtio balloon is done in a simple swap fashion which
 697  * follows these two macro steps:
 698  *  1) insert newpage into vb->pages list and update the host about it;
 699  *  2) update the host about the old page removed from vb->pages list;
 700  *
 701  * This function preforms the balloon page migration task.
 702  * Called through balloon_mapping->a_ops->migratepage
 703  */
 704 static int virtballoon_migratepage(struct balloon_dev_info *vb_dev_info,
 705                 struct page *newpage, struct page *page, enum migrate_mode mode)
 706 {
 707         struct virtio_balloon *vb = container_of(vb_dev_info,
 708                         struct virtio_balloon, vb_dev_info);
 709         unsigned long flags;
 710
 711         /*
 712          * In order to avoid lock contention while migrating pages concurrently
 713          * to leak_balloon() or fill_balloon() we just give up the balloon_lock
 714          * this turn, as it is easier to retry the page migration later.
 715          * This also prevents fill_balloon() getting stuck into a mutex
 716          * recursion in the case it ends up triggering memory compaction
 717          * while it is attempting to inflate the ballon.
 718          */
 719         if (!mutex_trylock(&vb->balloon_lock))
 720                 return -EAGAIN;
 721
 722         get_page(newpage); /* balloon reference */
 723
 724         /* balloon's page migration 1st step  -- inflate "newpage" */
 725         spin_lock_irqsave(&vb_dev_info->pages_lock, flags);
 726         balloon_page_insert(vb_dev_info, newpage);
 727         vb_dev_info->isolated_pages--;
 728         __count_vm_event(BALLOON_MIGRATE);
 729         spin_unlock_irqrestore(&vb_dev_info->pages_lock, flags);
 730         vb->num_pfns = VIRTIO_BALLOON_PAGES_PER_PAGE;
 731         set_page_pfns(vb, vb->pfns, newpage);
 732         tell_host(vb, vb->inflate_vq);
 733
 734         /* balloon's page migration 2nd step -- deflate "page" */
 735         spin_lock_irqsave(&vb_dev_info->pages_lock, flags);
 736         balloon_page_delete(page);
 737         spin_unlock_irqrestore(&vb_dev_info->pages_lock, flags);
 738         vb->num_pfns = VIRTIO_BALLOON_PAGES_PER_PAGE;
 739         set_page_pfns(vb, vb->pfns, page);
 740         tell_host(vb, vb->deflate_vq);
 741
 742         mutex_unlock(&vb->balloon_lock);
 743
 744         put_page(page); /* balloon reference */
 745
 746         return MIGRATEPAGE_SUCCESS;
 747 }
 748
 749 static int balloon_init_fs_context(struct fs_context *fc)
 750 {
 751         return init_pseudo(fc, BALLOON_KVM_MAGIC) ? 0 : -ENOMEM;
 752 }
 753
 754 static struct file_system_type balloon_fs = {
 755         .name           = "balloon-kvm",
 756         .init_fs_context = balloon_init_fs_context,
 757         .kill_sb        = kill_anon_super,
 758 };
 759
 760 #endif /* CONFIG_BALLOON_COMPACTION */
 761
 762 static unsigned long shrink_free_pages(struct virtio_balloon *vb,
 763                                        unsigned long pages_to_free)
 764 {
 765         unsigned long blocks_to_free, blocks_freed;
 766
 767         pages_to_free = round_up(pages_to_free,
 768                                  1 << VIRTIO_BALLOON_FREE_PAGE_ORDER);
 769         blocks_to_free = pages_to_free >> VIRTIO_BALLOON_FREE_PAGE_ORDER;
 770         blocks_freed = return_free_pages_to_mm(vb, blocks_to_free);
 771
 772         return blocks_freed << VIRTIO_BALLOON_FREE_PAGE_ORDER;
 773 }
 774
 775 static unsigned long shrink_balloon_pages(struct virtio_balloon *vb,
 776                                           unsigned long pages_to_free)
 777 {
 778         unsigned long pages_freed = 0;
 779
 780         /*
 781          * One invocation of leak_balloon can deflate at most
 782          * VIRTIO_BALLOON_ARRAY_PFNS_MAX balloon pages, so we call it
 783          * multiple times to deflate pages till reaching pages_to_free.
 784          */
 785         while (vb->num_pages && pages_to_free) {
 786                 pages_freed += leak_balloon(vb, pages_to_free) /
 787                                         VIRTIO_BALLOON_PAGES_PER_PAGE;
 788                 pages_to_free -= pages_freed;
 789         }
 790         update_balloon_size(vb);
 791
 792         return pages_freed;
 793 }
 794
 795 static unsigned long virtio_balloon_shrinker_scan(struct shrinker *shrinker,
 796                                                   struct shrink_control *sc)
 797 {
 798         unsigned long pages_to_free, pages_freed = 0;
 799         struct virtio_balloon *vb = container_of(shrinker,
 800                                         struct virtio_balloon, shrinker);
 801
 802         pages_to_free = sc->nr_to_scan * VIRTIO_BALLOON_PAGES_PER_PAGE;
 803
 804         if (virtio_has_feature(vb->vdev, VIRTIO_BALLOON_F_FREE_PAGE_HINT))
 805                 pages_freed = shrink_free_pages(vb, pages_to_free);
 806
 807         if (pages_freed >= pages_to_free)
 808                 return pages_freed;
 809
 810         pages_freed += shrink_balloon_pages(vb, pages_to_free - pages_freed);
 811
 812         return pages_freed;
 813 }
 814
 815 static unsigned long virtio_balloon_shrinker_count(struct shrinker *shrinker,
 816                                                    struct shrink_control *sc)
 817 {
 818         struct virtio_balloon *vb = container_of(shrinker,
 819                                         struct virtio_balloon, shrinker);
 820         unsigned long count;
 821
 822         count = vb->num_pages / VIRTIO_BALLOON_PAGES_PER_PAGE;
 823         count += vb->num_free_page_blocks >> VIRTIO_BALLOON_FREE_PAGE_ORDER;
 824
 825         return count;
 826 }
 827
 828 static void virtio_balloon_unregister_shrinker(struct virtio_balloon *vb)
 829 {
 830         unregister_shrinker(&vb->shrinker);
 831 }
 832
 833 static int virtio_balloon_register_shrinker(struct virtio_balloon *vb)
 834 {
 835         vb->shrinker.scan_objects = virtio_balloon_shrinker_scan;
 836         vb->shrinker.count_objects = virtio_balloon_shrinker_count;
 837         vb->shrinker.seeks = DEFAULT_SEEKS;
 838
 839         return register_shrinker(&vb->shrinker);
 840 }
 841
 842 static int virtballoon_probe(struct virtio_device *vdev)
 843 {
 844         struct virtio_balloon *vb;
 845         __u32 poison_val;
 846         int err;
 847
 848         if (!vdev->config->get) {
 849                 dev_err(&vdev->dev, "%s failure: config access disabled\n",
 850                         __func__);
 851                 return -EINVAL;
 852         }
 853
 854         vdev->priv = vb = kzalloc(sizeof(*vb), GFP_KERNEL);
 855         if (!vb) {
 856                 err = -ENOMEM;
 857                 goto out;
 858         }
 859
 860         INIT_WORK(&vb->update_balloon_stats_work, update_balloon_stats_func);
 861         INIT_WORK(&vb->update_balloon_size_work, update_balloon_size_func);
 862         spin_lock_init(&vb->stop_update_lock);
 863         mutex_init(&vb->balloon_lock);
 864         init_waitqueue_head(&vb->acked);
 865         vb->vdev = vdev;
 866
 867         balloon_devinfo_init(&vb->vb_dev_info);
 868
 869         err = init_vqs(vb);
 870         if (err)
 871                 goto out_free_vb;
 872
 873 #ifdef CONFIG_BALLOON_COMPACTION
 874         balloon_mnt = kern_mount(&balloon_fs);
 875         if (IS_ERR(balloon_mnt)) {
 876                 err = PTR_ERR(balloon_mnt);
 877                 goto out_del_vqs;
 878         }
 879
 880         vb->vb_dev_info.migratepage = virtballoon_migratepage;
 881         vb->vb_dev_info.inode = alloc_anon_inode(balloon_mnt->mnt_sb);
 882         if (IS_ERR(vb->vb_dev_info.inode)) {
 883                 err = PTR_ERR(vb->vb_dev_info.inode);
 884                 kern_unmount(balloon_mnt);
 885                 goto out_del_vqs;
 886         }
 887         vb->vb_dev_info.inode->i_mapping->a_ops = &balloon_aops;
 888 #endif
 889         if (virtio_has_feature(vdev, VIRTIO_BALLOON_F_FREE_PAGE_HINT)) {
 890                 /*
 891                  * There is always one entry reserved for cmd id, so the ring
 892                  * size needs to be at least two to report free page hints.
 893                  */
 894                 if (virtqueue_get_vring_size(vb->free_page_vq) < 2) {
 895                         err = -ENOSPC;
 896                         goto out_del_vqs;
 897                 }
 898                 vb->balloon_wq = alloc_workqueue("balloon-wq",
 899                                         WQ_FREEZABLE | WQ_CPU_INTENSIVE, 0);
 900                 if (!vb->balloon_wq) {
 901                         err = -ENOMEM;
 902                         goto out_del_vqs;
 903                 }
 904                 INIT_WORK(&vb->report_free_page_work, report_free_page_func);
 905                 vb->cmd_id_received_cache = VIRTIO_BALLOON_CMD_ID_STOP;
 906                 vb->cmd_id_active = cpu_to_virtio32(vb->vdev,
 907                                                   VIRTIO_BALLOON_CMD_ID_STOP);
 908                 vb->cmd_id_stop = cpu_to_virtio32(vb->vdev,
 909                                                   VIRTIO_BALLOON_CMD_ID_STOP);
 910                 spin_lock_init(&vb->free_page_list_lock);
 911                 INIT_LIST_HEAD(&vb->free_page_list);
 912                 if (virtio_has_feature(vdev, VIRTIO_BALLOON_F_PAGE_POISON)) {
 913                         memset(&poison_val, PAGE_POISON, sizeof(poison_val));
 914                         virtio_cwrite(vb->vdev, struct virtio_balloon_config,
 915                                       poison_val, &poison_val);
 916                 }
 917         }
 918         /*
 919          * We continue to use VIRTIO_BALLOON_F_DEFLATE_ON_OOM to decide if a
 920          * shrinker needs to be registered to relieve memory pressure.
 921          */
 922         if (virtio_has_feature(vb->vdev, VIRTIO_BALLOON_F_DEFLATE_ON_OOM)) {
 923                 err = virtio_balloon_register_shrinker(vb);
 924                 if (err)
 925                         goto out_del_balloon_wq;
 926         }
 927         virtio_device_ready(vdev);
 928
 929         if (towards_target(vb))
 930                 virtballoon_changed(vdev);
 931         return 0;
 932
 933 out_del_balloon_wq:
 934         if (virtio_has_feature(vdev, VIRTIO_BALLOON_F_FREE_PAGE_HINT))
 935                 destroy_workqueue(vb->balloon_wq);
 936 out_del_vqs:
 937         vdev->config->del_vqs(vdev);
 938 out_free_vb:
 939         kfree(vb);
 940 out:
 941         return err;
 942 }
 943
 944 static void remove_common(struct virtio_balloon *vb)
 945 {
 946         /* There might be pages left in the balloon: free them. */
 947         while (vb->num_pages)
 948                 leak_balloon(vb, vb->num_pages);
 949         update_balloon_size(vb);
 950
 951         /* Now we reset the device so we can clean up the queues. */
 952         vb->vdev->config->reset(vb->vdev);
 953
 954         vb->vdev->config->del_vqs(vb->vdev);
 955 }
 956
 957 static void virtballoon_remove(struct virtio_device *vdev)
 958 {
 959         struct virtio_balloon *vb = vdev->priv;
 960
 961         if (virtio_has_feature(vb->vdev, VIRTIO_BALLOON_F_DEFLATE_ON_OOM))
 962                 virtio_balloon_unregister_shrinker(vb);
 963         spin_lock_irq(&vb->stop_update_lock);
 964         vb->stop_update = true;
 965         spin_unlock_irq(&vb->stop_update_lock);
 966         cancel_work_sync(&vb->update_balloon_size_work);
 967         cancel_work_sync(&vb->update_balloon_stats_work);
 968
 969         if (virtio_has_feature(vdev, VIRTIO_BALLOON_F_FREE_PAGE_HINT)) {
 970                 cancel_work_sync(&vb->report_free_page_work);
 971                 destroy_workqueue(vb->balloon_wq);
 972         }
 973
 974         remove_common(vb);
 975 #ifdef CONFIG_BALLOON_COMPACTION
 976         if (vb->vb_dev_info.inode)
 977                 iput(vb->vb_dev_info.inode);
 978
 979         kern_unmount(balloon_mnt);
 980 #endif
 981         kfree(vb);
 982 }
 983
 984 #ifdef CONFIG_PM_SLEEP
 985 static int virtballoon_freeze(struct virtio_device *vdev)
 986 {
 987         struct virtio_balloon *vb = vdev->priv;
 988
 989         /*
 990          * The workqueue is already frozen by the PM core before this
 991          * function is called.
 992          */
 993         remove_common(vb);
 994         return 0;
 995 }
 996
 997 static int virtballoon_restore(struct virtio_device *vdev)
 998 {
 999         struct virtio_balloon *vb = vdev->priv;
1000         int ret;
1001
1002         ret = init_vqs(vdev->priv);
1003         if (ret)
1004                 return ret;
1005
1006         virtio_device_ready(vdev);
1007
1008         if (towards_target(vb))
1009                 virtballoon_changed(vdev);
1010         update_balloon_size(vb);
1011         return 0;
1012 }
1013 #endif
1014
1015 static int virtballoon_validate(struct virtio_device *vdev)
1016 {
1017         if (!page_poisoning_enabled())
1018                 __virtio_clear_bit(vdev, VIRTIO_BALLOON_F_PAGE_POISON);
1019
1020         __virtio_clear_bit(vdev, VIRTIO_F_IOMMU_PLATFORM);
1021         return 0;
1022 }
1023
1024 static unsigned int features[] = {
1025         VIRTIO_BALLOON_F_MUST_TELL_HOST,
1026         VIRTIO_BALLOON_F_STATS_VQ,
1027         VIRTIO_BALLOON_F_DEFLATE_ON_OOM,
1028         VIRTIO_BALLOON_F_FREE_PAGE_HINT,
1029         VIRTIO_BALLOON_F_PAGE_POISON,
1030 };
1031
1032 static struct virtio_driver virtio_balloon_driver = {
1033         .feature_table = features,
1034         .feature_table_size = ARRAY_SIZE(features),
1035         .driver.name =  KBUILD_MODNAME,
1036         .driver.owner = THIS_MODULE,
1037         .id_table =     id_table,
1038         .validate =     virtballoon_validate,
1039         .probe =        virtballoon_probe,
1040         .remove =       virtballoon_remove,
1041         .config_changed = virtballoon_changed,
1042 #ifdef CONFIG_PM_SLEEP
1043         .freeze =       virtballoon_freeze,
1044         .restore =      virtballoon_restore,
1045 #endif
1046 };
1047
1048 module_virtio_driver(virtio_balloon_driver);
1049 MODULE_DEVICE_TABLE(virtio, id_table);
1050 MODULE_DESCRIPTION("Virtio balloon driver");
1051 MODULE_LICENSE("GPL");