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