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
  31 /*
  32  * Balloon device works in 4K page units.  So each page is pointed to by
  33  * multiple balloon pages.  All memory counters in this driver are in balloon
  34  * page units.
  35  */
  36 #define VIRTIO_BALLOON_PAGES_PER_PAGE (PAGE_SIZE >> VIRTIO_BALLOON_PFN_SHIFT)
  37
  38 struct virtio_balloon
  39 {
  40         struct virtio_device *vdev;
  41         struct virtqueue *inflate_vq, *deflate_vq, *stats_vq;
  42
  43         /* Where the ballooning thread waits for config to change. */
  44         wait_queue_head_t config_change;
  45
  46         /* The thread servicing the balloon. */
  47         struct task_struct *thread;
  48
  49         /* Waiting for host to ack the pages we released. */
  50         wait_queue_head_t acked;
  51
  52         /* Number of balloon pages we've told the Host we're not using. */
  53         unsigned int num_pages;
  54         /*
  55          * The pages we've told the Host we're not using.
  56          * Each page on this list adds VIRTIO_BALLOON_PAGES_PER_PAGE
  57          * to num_pages above.
  58          */
  59         struct list_head pages;
  60
  61         /* The array of pfns we tell the Host about. */
  62         unsigned int num_pfns;
  63         u32 pfns[256];
  64
  65         /* Memory statistics */
  66         int need_stats_update;
  67         struct virtio_balloon_stat stats[VIRTIO_BALLOON_S_NR];
  68 };
  69
  70 static struct virtio_device_id id_table[] = {
  71         { VIRTIO_ID_BALLOON, VIRTIO_DEV_ANY_ID },
  72         { 0 },
  73 };
  74
  75 static u32 page_to_balloon_pfn(struct page *page)
  76 {
  77         unsigned long pfn = page_to_pfn(page);
  78
  79         BUILD_BUG_ON(PAGE_SHIFT < VIRTIO_BALLOON_PFN_SHIFT);
  80         /* Convert pfn from Linux page size to balloon page size. */
  81         return pfn * VIRTIO_BALLOON_PAGES_PER_PAGE;
  82 }
  83
  84 static struct page *balloon_pfn_to_page(u32 pfn)
  85 {
  86         BUG_ON(pfn % VIRTIO_BALLOON_PAGES_PER_PAGE);
  87         return pfn_to_page(pfn / VIRTIO_BALLOON_PAGES_PER_PAGE);
  88 }
  89
  90 static void balloon_ack(struct virtqueue *vq)
  91 {
  92         struct virtio_balloon *vb = vq->vdev->priv;
  93
  94         wake_up(&vb->acked);
  95 }
  96
  97 static void tell_host(struct virtio_balloon *vb, struct virtqueue *vq)
  98 {
  99         struct scatterlist sg;
 100         unsigned int len;
 101
 102         sg_init_one(&sg, vb->pfns, sizeof(vb->pfns[0]) * vb->num_pfns);
 103
 104         /* We should always be able to add one buffer to an empty queue. */
 105         if (virtqueue_add_buf(vq, &sg, 1, 0, vb, GFP_KERNEL) < 0)
 106                 BUG();
 107         virtqueue_kick(vq);
 108
 109         /* When host has read buffer, this completes via balloon_ack */
 110         wait_event(vb->acked, virtqueue_get_buf(vq, &len));
 111 }
 112
 113 static void set_page_pfns(u32 pfns[], struct page *page)
 114 {
 115         unsigned int i;
 116
 117         /* Set balloon pfns pointing at this page.
 118          * Note that the first pfn points at start of the page. */
 119         for (i = 0; i < VIRTIO_BALLOON_PAGES_PER_PAGE; i++)
 120                 pfns[i] = page_to_balloon_pfn(page) + i;
 121 }
 122
 123 static void fill_balloon(struct virtio_balloon *vb, size_t num)
 124 {
 125         /* We can only do one array worth at a time. */
 126         num = min(num, ARRAY_SIZE(vb->pfns));
 127
 128         for (vb->num_pfns = 0; vb->num_pfns < num;
 129              vb->num_pfns += VIRTIO_BALLOON_PAGES_PER_PAGE) {
 130                 struct page *page = alloc_page(GFP_HIGHUSER | __GFP_NORETRY |
 131                                         __GFP_NOMEMALLOC | __GFP_NOWARN);
 132                 if (!page) {
 133                         if (printk_ratelimit())
 134                                 dev_printk(KERN_INFO, &vb->vdev->dev,
 135                                            "Out of puff! Can't get %zu pages\n",
 136                                            num);
 137                         /* Sleep for at least 1/5 of a second before retry. */
 138                         msleep(200);
 139                         break;
 140                 }
 141                 set_page_pfns(vb->pfns + vb->num_pfns, page);
 142                 vb->num_pages += VIRTIO_BALLOON_PAGES_PER_PAGE;
 143                 totalram_pages--;
 144                 list_add(&page->lru, &vb->pages);
 145         }
 146
 147         /* Didn't get any?  Oh well. */
 148         if (vb->num_pfns == 0)
 149                 return;
 150
 151         tell_host(vb, vb->inflate_vq);
 152 }
 153
 154 static void release_pages_by_pfn(const u32 pfns[], unsigned int num)
 155 {
 156         unsigned int i;
 157
 158         /* Find pfns pointing at start of each page, get pages and free them. */
 159         for (i = 0; i < num; i += VIRTIO_BALLOON_PAGES_PER_PAGE) {
 160                 __free_page(balloon_pfn_to_page(pfns[i]));
 161                 totalram_pages++;
 162         }
 163 }
 164
 165 static void leak_balloon(struct virtio_balloon *vb, size_t num)
 166 {
 167         struct page *page;
 168
 169         /* We can only do one array worth at a time. */
 170         num = min(num, ARRAY_SIZE(vb->pfns));
 171
 172         for (vb->num_pfns = 0; vb->num_pfns < num;
 173              vb->num_pfns += VIRTIO_BALLOON_PAGES_PER_PAGE) {
 174                 page = list_first_entry(&vb->pages, struct page, lru);
 175                 list_del(&page->lru);
 176                 set_page_pfns(vb->pfns + vb->num_pfns, page);
 177                 vb->num_pages -= VIRTIO_BALLOON_PAGES_PER_PAGE;
 178         }
 179
 180         /*
 181          * Note that if
 182          * virtio_has_feature(vdev, VIRTIO_BALLOON_F_MUST_TELL_HOST);
 183          * is true, we *have* to do it in this order
 184          */
 185         tell_host(vb, vb->deflate_vq);
 186         release_pages_by_pfn(vb->pfns, vb->num_pfns);
 187 }
 188
 189 static inline void update_stat(struct virtio_balloon *vb, int idx,
 190                                u16 tag, u64 val)
 191 {
 192         BUG_ON(idx >= VIRTIO_BALLOON_S_NR);
 193         vb->stats[idx].tag = tag;
 194         vb->stats[idx].val = val;
 195 }
 196
 197 #define pages_to_bytes(x) ((u64)(x) << PAGE_SHIFT)
 198
 199 static void update_balloon_stats(struct virtio_balloon *vb)
 200 {
 201         unsigned long events[NR_VM_EVENT_ITEMS];
 202         struct sysinfo i;
 203         int idx = 0;
 204
 205         all_vm_events(events);
 206         si_meminfo(&i);
 207
 208         update_stat(vb, idx++, VIRTIO_BALLOON_S_SWAP_IN,
 209                                 pages_to_bytes(events[PSWPIN]));
 210         update_stat(vb, idx++, VIRTIO_BALLOON_S_SWAP_OUT,
 211                                 pages_to_bytes(events[PSWPOUT]));
 212         update_stat(vb, idx++, VIRTIO_BALLOON_S_MAJFLT, events[PGMAJFAULT]);
 213         update_stat(vb, idx++, VIRTIO_BALLOON_S_MINFLT, events[PGFAULT]);
 214         update_stat(vb, idx++, VIRTIO_BALLOON_S_MEMFREE,
 215                                 pages_to_bytes(i.freeram));
 216         update_stat(vb, idx++, VIRTIO_BALLOON_S_MEMTOT,
 217                                 pages_to_bytes(i.totalram));
 218 }
 219
 220 /*
 221  * While most virtqueues communicate guest-initiated requests to the hypervisor,
 222  * the stats queue operates in reverse.  The driver initializes the virtqueue
 223  * with a single buffer.  From that point forward, all conversations consist of
 224  * a hypervisor request (a call to this function) which directs us to refill
 225  * the virtqueue with a fresh stats buffer.  Since stats collection can sleep,
 226  * we notify our kthread which does the actual work via stats_handle_request().
 227  */
 228 static void stats_request(struct virtqueue *vq)
 229 {
 230         struct virtio_balloon *vb = vq->vdev->priv;
 231
 232         vb->need_stats_update = 1;
 233         wake_up(&vb->config_change);
 234 }
 235
 236 static void stats_handle_request(struct virtio_balloon *vb)
 237 {
 238         struct virtqueue *vq;
 239         struct scatterlist sg;
 240         unsigned int len;
 241
 242         vb->need_stats_update = 0;
 243         update_balloon_stats(vb);
 244
 245         vq = vb->stats_vq;
 246         if (!virtqueue_get_buf(vq, &len))
 247                 return;
 248         sg_init_one(&sg, vb->stats, sizeof(vb->stats));
 249         if (virtqueue_add_buf(vq, &sg, 1, 0, vb, GFP_KERNEL) < 0)
 250                 BUG();
 251         virtqueue_kick(vq);
 252 }
 253
 254 static void virtballoon_changed(struct virtio_device *vdev)
 255 {
 256         struct virtio_balloon *vb = vdev->priv;
 257
 258         wake_up(&vb->config_change);
 259 }
 260
 261 static inline s64 towards_target(struct virtio_balloon *vb)
 262 {
 263         __le32 v;
 264         s64 target;
 265
 266         vb->vdev->config->get(vb->vdev,
 267                               offsetof(struct virtio_balloon_config, num_pages),
 268                               &v, sizeof(v));
 269         target = le32_to_cpu(v);
 270         return target - vb->num_pages;
 271 }
 272
 273 static void update_balloon_size(struct virtio_balloon *vb)
 274 {
 275         __le32 actual = cpu_to_le32(vb->num_pages);
 276
 277         vb->vdev->config->set(vb->vdev,
 278                               offsetof(struct virtio_balloon_config, actual),
 279                               &actual, sizeof(actual));
 280 }
 281
 282 static int balloon(void *_vballoon)
 283 {
 284         struct virtio_balloon *vb = _vballoon;
 285
 286         set_freezable();
 287         while (!kthread_should_stop()) {
 288                 s64 diff;
 289
 290                 try_to_freeze();
 291                 wait_event_interruptible(vb->config_change,
 292                                          (diff = towards_target(vb)) != 0
 293                                          || vb->need_stats_update
 294                                          || kthread_should_stop()
 295                                          || freezing(current));
 296                 if (vb->need_stats_update)
 297                         stats_handle_request(vb);
 298                 if (diff > 0)
 299                         fill_balloon(vb, diff);
 300                 else if (diff < 0)
 301                         leak_balloon(vb, -diff);
 302                 update_balloon_size(vb);
 303         }
 304         return 0;
 305 }
 306
 307 static int init_vqs(struct virtio_balloon *vb)
 308 {
 309         struct virtqueue *vqs[3];
 310         vq_callback_t *callbacks[] = { balloon_ack, balloon_ack, stats_request };
 311         const char *names[] = { "inflate", "deflate", "stats" };
 312         int err, nvqs;
 313
 314         /*
 315          * We expect two virtqueues: inflate and deflate, and
 316          * optionally stat.
 317          */
 318         nvqs = virtio_has_feature(vb->vdev, VIRTIO_BALLOON_F_STATS_VQ) ? 3 : 2;
 319         err = vb->vdev->config->find_vqs(vb->vdev, nvqs, vqs, callbacks, names);
 320         if (err)
 321                 return err;
 322
 323         vb->inflate_vq = vqs[0];
 324         vb->deflate_vq = vqs[1];
 325         if (virtio_has_feature(vb->vdev, VIRTIO_BALLOON_F_STATS_VQ)) {
 326                 struct scatterlist sg;
 327                 vb->stats_vq = vqs[2];
 328
 329                 /*
 330                  * Prime this virtqueue with one buffer so the hypervisor can
 331                  * use it to signal us later.
 332                  */
 333                 sg_init_one(&sg, vb->stats, sizeof vb->stats);
 334                 if (virtqueue_add_buf(vb->stats_vq, &sg, 1, 0, vb, GFP_KERNEL)
 335                     < 0)
 336                         BUG();
 337                 virtqueue_kick(vb->stats_vq);
 338         }
 339         return 0;
 340 }
 341
 342 static int virtballoon_probe(struct virtio_device *vdev)
 343 {
 344         struct virtio_balloon *vb;
 345         int err;
 346
 347         vdev->priv = vb = kmalloc(sizeof(*vb), GFP_KERNEL);
 348         if (!vb) {
 349                 err = -ENOMEM;
 350                 goto out;
 351         }
 352
 353         INIT_LIST_HEAD(&vb->pages);
 354         vb->num_pages = 0;
 355         init_waitqueue_head(&vb->config_change);
 356         init_waitqueue_head(&vb->acked);
 357         vb->vdev = vdev;
 358         vb->need_stats_update = 0;
 359
 360         err = init_vqs(vb);
 361         if (err)
 362                 goto out_free_vb;
 363
 364         vb->thread = kthread_run(balloon, vb, "vballoon");
 365         if (IS_ERR(vb->thread)) {
 366                 err = PTR_ERR(vb->thread);
 367                 goto out_del_vqs;
 368         }
 369
 370         return 0;
 371
 372 out_del_vqs:
 373         vdev->config->del_vqs(vdev);
 374 out_free_vb:
 375         kfree(vb);
 376 out:
 377         return err;
 378 }
 379
 380 static void remove_common(struct virtio_balloon *vb)
 381 {
 382         /* There might be pages left in the balloon: free them. */
 383         while (vb->num_pages)
 384                 leak_balloon(vb, vb->num_pages);
 385         update_balloon_size(vb);
 386
 387         /* Now we reset the device so we can clean up the queues. */
 388         vb->vdev->config->reset(vb->vdev);
 389
 390         vb->vdev->config->del_vqs(vb->vdev);
 391 }
 392
 393 static void __devexit virtballoon_remove(struct virtio_device *vdev)
 394 {
 395         struct virtio_balloon *vb = vdev->priv;
 396
 397         kthread_stop(vb->thread);
 398         remove_common(vb);
 399         kfree(vb);
 400 }
 401
 402 #ifdef CONFIG_PM
 403 static int virtballoon_freeze(struct virtio_device *vdev)
 404 {
 405         struct virtio_balloon *vb = vdev->priv;
 406
 407         /*
 408          * The kthread is already frozen by the PM core before this
 409          * function is called.
 410          */
 411
 412         remove_common(vb);
 413         return 0;
 414 }
 415
 416 static int virtballoon_restore(struct virtio_device *vdev)
 417 {
 418         struct virtio_balloon *vb = vdev->priv;
 419         int ret;
 420
 421         ret = init_vqs(vdev->priv);
 422         if (ret)
 423                 return ret;
 424
 425         fill_balloon(vb, towards_target(vb));
 426         update_balloon_size(vb);
 427         return 0;
 428 }
 429 #endif
 430
 431 static unsigned int features[] = {
 432         VIRTIO_BALLOON_F_MUST_TELL_HOST,
 433         VIRTIO_BALLOON_F_STATS_VQ,
 434 };
 435
 436 static struct virtio_driver virtio_balloon_driver = {
 437         .feature_table = features,
 438         .feature_table_size = ARRAY_SIZE(features),
 439         .driver.name =  KBUILD_MODNAME,
 440         .driver.owner = THIS_MODULE,
 441         .id_table =     id_table,
 442         .probe =        virtballoon_probe,
 443         .remove =       __devexit_p(virtballoon_remove),
 444         .config_changed = virtballoon_changed,
 445 #ifdef CONFIG_PM
 446         .freeze =       virtballoon_freeze,
 447         .restore =      virtballoon_restore,
 448 #endif
 449 };
 450
 451 static int __init init(void)
 452 {
 453         return register_virtio_driver(&virtio_balloon_driver);
 454 }
 455
 456 static void __exit fini(void)
 457 {
 458         unregister_virtio_driver(&virtio_balloon_driver);
 459 }
 460 module_init(init);
 461 module_exit(fini);
 462
 463 MODULE_DEVICE_TABLE(virtio, id_table);
 464 MODULE_DESCRIPTION("Virtio balloon driver");
 465 MODULE_LICENSE("GPL");