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         struct completion 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;
  93         unsigned int len;
  94
  95         vb = virtqueue_get_buf(vq, &len);
  96         if (vb)
  97                 complete(&vb->acked);
  98 }
  99
 100 static void tell_host(struct virtio_balloon *vb, struct virtqueue *vq)
 101 {
 102         struct scatterlist sg;
 103
 104         sg_init_one(&sg, vb->pfns, sizeof(vb->pfns[0]) * vb->num_pfns);
 105
 106         init_completion(&vb->acked);
 107
 108         /* We should always be able to add one buffer to an empty queue. */
 109         if (virtqueue_add_buf(vq, &sg, 1, 0, vb, GFP_KERNEL) < 0)
 110                 BUG();
 111         virtqueue_kick(vq);
 112
 113         /* When host has read buffer, this completes via balloon_ack */
 114         wait_for_completion(&vb->acked);
 115 }
 116
 117 static void set_page_pfns(u32 pfns[], struct page *page)
 118 {
 119         unsigned int i;
 120
 121         /* Set balloon pfns pointing at this page.
 122          * Note that the first pfn points at start of the page. */
 123         for (i = 0; i < VIRTIO_BALLOON_PAGES_PER_PAGE; i++)
 124                 pfns[i] = page_to_balloon_pfn(page) + i;
 125 }
 126
 127 static void fill_balloon(struct virtio_balloon *vb, size_t num)
 128 {
 129         /* We can only do one array worth at a time. */
 130         num = min(num, ARRAY_SIZE(vb->pfns));
 131
 132         for (vb->num_pfns = 0; vb->num_pfns < num;
 133              vb->num_pfns += VIRTIO_BALLOON_PAGES_PER_PAGE) {
 134                 struct page *page = alloc_page(GFP_HIGHUSER | __GFP_NORETRY |
 135                                         __GFP_NOMEMALLOC | __GFP_NOWARN);
 136                 if (!page) {
 137                         if (printk_ratelimit())
 138                                 dev_printk(KERN_INFO, &vb->vdev->dev,
 139                                            "Out of puff! Can't get %zu pages\n",
 140                                            num);
 141                         /* Sleep for at least 1/5 of a second before retry. */
 142                         msleep(200);
 143                         break;
 144                 }
 145                 set_page_pfns(vb->pfns + vb->num_pfns, page);
 146                 vb->num_pages += VIRTIO_BALLOON_PAGES_PER_PAGE;
 147                 totalram_pages--;
 148                 list_add(&page->lru, &vb->pages);
 149         }
 150
 151         /* Didn't get any?  Oh well. */
 152         if (vb->num_pfns == 0)
 153                 return;
 154
 155         tell_host(vb, vb->inflate_vq);
 156 }
 157
 158 static void release_pages_by_pfn(const u32 pfns[], unsigned int num)
 159 {
 160         unsigned int i;
 161
 162         /* Find pfns pointing at start of each page, get pages and free them. */
 163         for (i = 0; i < num; i += VIRTIO_BALLOON_PAGES_PER_PAGE) {
 164                 __free_page(balloon_pfn_to_page(pfns[i]));
 165                 totalram_pages++;
 166         }
 167 }
 168
 169 static void leak_balloon(struct virtio_balloon *vb, size_t num)
 170 {
 171         struct page *page;
 172
 173         /* We can only do one array worth at a time. */
 174         num = min(num, ARRAY_SIZE(vb->pfns));
 175
 176         for (vb->num_pfns = 0; vb->num_pfns < num;
 177              vb->num_pfns += VIRTIO_BALLOON_PAGES_PER_PAGE) {
 178                 page = list_first_entry(&vb->pages, struct page, lru);
 179                 list_del(&page->lru);
 180                 set_page_pfns(vb->pfns + vb->num_pfns, page);
 181                 vb->num_pages -= VIRTIO_BALLOON_PAGES_PER_PAGE;
 182         }
 183
 184         /*
 185          * Note that if
 186          * virtio_has_feature(vdev, VIRTIO_BALLOON_F_MUST_TELL_HOST);
 187          * is true, we *have* to do it in this order
 188          */
 189         tell_host(vb, vb->deflate_vq);
 190         release_pages_by_pfn(vb->pfns, vb->num_pfns);
 191 }
 192
 193 static inline void update_stat(struct virtio_balloon *vb, int idx,
 194                                u16 tag, u64 val)
 195 {
 196         BUG_ON(idx >= VIRTIO_BALLOON_S_NR);
 197         vb->stats[idx].tag = tag;
 198         vb->stats[idx].val = val;
 199 }
 200
 201 #define pages_to_bytes(x) ((u64)(x) << PAGE_SHIFT)
 202
 203 static void update_balloon_stats(struct virtio_balloon *vb)
 204 {
 205         unsigned long events[NR_VM_EVENT_ITEMS];
 206         struct sysinfo i;
 207         int idx = 0;
 208
 209         all_vm_events(events);
 210         si_meminfo(&i);
 211
 212         update_stat(vb, idx++, VIRTIO_BALLOON_S_SWAP_IN,
 213                                 pages_to_bytes(events[PSWPIN]));
 214         update_stat(vb, idx++, VIRTIO_BALLOON_S_SWAP_OUT,
 215                                 pages_to_bytes(events[PSWPOUT]));
 216         update_stat(vb, idx++, VIRTIO_BALLOON_S_MAJFLT, events[PGMAJFAULT]);
 217         update_stat(vb, idx++, VIRTIO_BALLOON_S_MINFLT, events[PGFAULT]);
 218         update_stat(vb, idx++, VIRTIO_BALLOON_S_MEMFREE,
 219                                 pages_to_bytes(i.freeram));
 220         update_stat(vb, idx++, VIRTIO_BALLOON_S_MEMTOT,
 221                                 pages_to_bytes(i.totalram));
 222 }
 223
 224 /*
 225  * While most virtqueues communicate guest-initiated requests to the hypervisor,
 226  * the stats queue operates in reverse.  The driver initializes the virtqueue
 227  * with a single buffer.  From that point forward, all conversations consist of
 228  * a hypervisor request (a call to this function) which directs us to refill
 229  * the virtqueue with a fresh stats buffer.  Since stats collection can sleep,
 230  * we notify our kthread which does the actual work via stats_handle_request().
 231  */
 232 static void stats_request(struct virtqueue *vq)
 233 {
 234         struct virtio_balloon *vb;
 235         unsigned int len;
 236
 237         vb = virtqueue_get_buf(vq, &len);
 238         if (!vb)
 239                 return;
 240         vb->need_stats_update = 1;
 241         wake_up(&vb->config_change);
 242 }
 243
 244 static void stats_handle_request(struct virtio_balloon *vb)
 245 {
 246         struct virtqueue *vq;
 247         struct scatterlist sg;
 248
 249         vb->need_stats_update = 0;
 250         update_balloon_stats(vb);
 251
 252         vq = vb->stats_vq;
 253         sg_init_one(&sg, vb->stats, sizeof(vb->stats));
 254         if (virtqueue_add_buf(vq, &sg, 1, 0, vb, GFP_KERNEL) < 0)
 255                 BUG();
 256         virtqueue_kick(vq);
 257 }
 258
 259 static void virtballoon_changed(struct virtio_device *vdev)
 260 {
 261         struct virtio_balloon *vb = vdev->priv;
 262
 263         wake_up(&vb->config_change);
 264 }
 265
 266 static inline s64 towards_target(struct virtio_balloon *vb)
 267 {
 268         __le32 v;
 269         s64 target;
 270
 271         vb->vdev->config->get(vb->vdev,
 272                               offsetof(struct virtio_balloon_config, num_pages),
 273                               &v, sizeof(v));
 274         target = le32_to_cpu(v);
 275         return target - vb->num_pages;
 276 }
 277
 278 static void update_balloon_size(struct virtio_balloon *vb)
 279 {
 280         __le32 actual = cpu_to_le32(vb->num_pages);
 281
 282         vb->vdev->config->set(vb->vdev,
 283                               offsetof(struct virtio_balloon_config, actual),
 284                               &actual, sizeof(actual));
 285 }
 286
 287 static int balloon(void *_vballoon)
 288 {
 289         struct virtio_balloon *vb = _vballoon;
 290
 291         set_freezable();
 292         while (!kthread_should_stop()) {
 293                 s64 diff;
 294
 295                 try_to_freeze();
 296                 wait_event_interruptible(vb->config_change,
 297                                          (diff = towards_target(vb)) != 0
 298                                          || vb->need_stats_update
 299                                          || kthread_should_stop()
 300                                          || freezing(current));
 301                 if (vb->need_stats_update)
 302                         stats_handle_request(vb);
 303                 if (diff > 0)
 304                         fill_balloon(vb, diff);
 305                 else if (diff < 0)
 306                         leak_balloon(vb, -diff);
 307                 update_balloon_size(vb);
 308         }
 309         return 0;
 310 }
 311
 312 static int init_vqs(struct virtio_balloon *vb)
 313 {
 314         struct virtqueue *vqs[3];
 315         vq_callback_t *callbacks[] = { balloon_ack, balloon_ack, stats_request };
 316         const char *names[] = { "inflate", "deflate", "stats" };
 317         int err, nvqs;
 318
 319         /*
 320          * We expect two virtqueues: inflate and deflate, and
 321          * optionally stat.
 322          */
 323         nvqs = virtio_has_feature(vb->vdev, VIRTIO_BALLOON_F_STATS_VQ) ? 3 : 2;
 324         err = vb->vdev->config->find_vqs(vb->vdev, nvqs, vqs, callbacks, names);
 325         if (err)
 326                 return err;
 327
 328         vb->inflate_vq = vqs[0];
 329         vb->deflate_vq = vqs[1];
 330         if (virtio_has_feature(vb->vdev, VIRTIO_BALLOON_F_STATS_VQ)) {
 331                 struct scatterlist sg;
 332                 vb->stats_vq = vqs[2];
 333
 334                 /*
 335                  * Prime this virtqueue with one buffer so the hypervisor can
 336                  * use it to signal us later.
 337                  */
 338                 sg_init_one(&sg, vb->stats, sizeof vb->stats);
 339                 if (virtqueue_add_buf(vb->stats_vq, &sg, 1, 0, vb, GFP_KERNEL)
 340                     < 0)
 341                         BUG();
 342                 virtqueue_kick(vb->stats_vq);
 343         }
 344         return 0;
 345 }
 346
 347 static int virtballoon_probe(struct virtio_device *vdev)
 348 {
 349         struct virtio_balloon *vb;
 350         int err;
 351
 352         vdev->priv = vb = kmalloc(sizeof(*vb), GFP_KERNEL);
 353         if (!vb) {
 354                 err = -ENOMEM;
 355                 goto out;
 356         }
 357
 358         INIT_LIST_HEAD(&vb->pages);
 359         vb->num_pages = 0;
 360         init_waitqueue_head(&vb->config_change);
 361         vb->vdev = vdev;
 362         vb->need_stats_update = 0;
 363
 364         err = init_vqs(vb);
 365         if (err)
 366                 goto out_free_vb;
 367
 368         vb->thread = kthread_run(balloon, vb, "vballoon");
 369         if (IS_ERR(vb->thread)) {
 370                 err = PTR_ERR(vb->thread);
 371                 goto out_del_vqs;
 372         }
 373
 374         return 0;
 375
 376 out_del_vqs:
 377         vdev->config->del_vqs(vdev);
 378 out_free_vb:
 379         kfree(vb);
 380 out:
 381         return err;
 382 }
 383
 384 static void __devexit virtballoon_remove(struct virtio_device *vdev)
 385 {
 386         struct virtio_balloon *vb = vdev->priv;
 387
 388         kthread_stop(vb->thread);
 389
 390         /* There might be pages left in the balloon: free them. */
 391         while (vb->num_pages)
 392                 leak_balloon(vb, vb->num_pages);
 393
 394         /* Now we reset the device so we can clean up the queues. */
 395         vdev->config->reset(vdev);
 396
 397         vdev->config->del_vqs(vdev);
 398         kfree(vb);
 399 }
 400
 401 #ifdef CONFIG_PM
 402 static int virtballoon_freeze(struct virtio_device *vdev)
 403 {
 404         struct virtio_balloon *vb = vdev->priv;
 405
 406         /*
 407          * The kthread is already frozen by the PM core before this
 408          * function is called.
 409          */
 410
 411         while (vb->num_pages)
 412                 leak_balloon(vb, vb->num_pages);
 413         update_balloon_size(vb);
 414
 415         /* Ensure we don't get any more requests from the host */
 416         vdev->config->reset(vdev);
 417         vdev->config->del_vqs(vdev);
 418         return 0;
 419 }
 420
 421 static int restore_common(struct virtio_device *vdev)
 422 {
 423         struct virtio_balloon *vb = vdev->priv;
 424         int ret;
 425
 426         ret = init_vqs(vdev->priv);
 427         if (ret)
 428                 return ret;
 429
 430         fill_balloon(vb, towards_target(vb));
 431         update_balloon_size(vb);
 432         return 0;
 433 }
 434
 435 static int virtballoon_restore(struct virtio_device *vdev)
 436 {
 437         return restore_common(vdev);
 438 }
 439 #endif
 440
 441 static unsigned int features[] = {
 442         VIRTIO_BALLOON_F_MUST_TELL_HOST,
 443         VIRTIO_BALLOON_F_STATS_VQ,
 444 };
 445
 446 static struct virtio_driver virtio_balloon_driver = {
 447         .feature_table = features,
 448         .feature_table_size = ARRAY_SIZE(features),
 449         .driver.name =  KBUILD_MODNAME,
 450         .driver.owner = THIS_MODULE,
 451         .id_table =     id_table,
 452         .probe =        virtballoon_probe,
 453         .remove =       __devexit_p(virtballoon_remove),
 454         .config_changed = virtballoon_changed,
 455 #ifdef CONFIG_PM
 456         .freeze =       virtballoon_freeze,
 457         .restore =      virtballoon_restore,
 458 #endif
 459 };
 460
 461 static int __init init(void)
 462 {
 463         return register_virtio_driver(&virtio_balloon_driver);
 464 }
 465
 466 static void __exit fini(void)
 467 {
 468         unregister_virtio_driver(&virtio_balloon_driver);
 469 }
 470 module_init(init);
 471 module_exit(fini);
 472
 473 MODULE_DEVICE_TABLE(virtio, id_table);
 474 MODULE_DESCRIPTION("Virtio balloon driver");
 475 MODULE_LICENSE("GPL");