drivers/virtio/virtio_balloon.c

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