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