drivers/virtio/virtio_balloon.c

   1 /* Virtio balloon implementation, inspired by Dor Loar and Marcelo
   2  * Tosatti's implementations.
   3  *
   4  *  Copyright 2008 Rusty Russell IBM Corporation
   5  *
   6  *  This program is free software; you can redistribute it and/or modify
   7  *  it under the terms of the GNU General Public License as published by
   8  *  the Free Software Foundation; either version 2 of the License, or
   9  *  (at your option) any later version.
  10  *
  11  *  This program is distributed in the hope that it will be useful,
  12  *  but WITHOUT ANY WARRANTY; without even the implied warranty of
  13  *  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  14  *  GNU General Public License for more details.
  15  *
  16  *  You should have received a copy of the GNU General Public License
  17  *  along with this program; if not, write to the Free Software
  18  *  Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA  02110-1301  USA
  19  */
  20 //#define DEBUG
  21 #include <linux/virtio.h>
  22 #include <linux/virtio_balloon.h>
  23 #include <linux/swap.h>
  24 #include <linux/kthread.h>
  25 #include <linux/freezer.h>
  26 #include <linux/delay.h>
  27 #include <linux/slab.h>
  28
  29 struct virtio_balloon
  30 {
  31         struct virtio_device *vdev;
  32         struct virtqueue *inflate_vq, *deflate_vq, *stats_vq;
  33
  34         /* Where the ballooning thread waits for config to change. */
  35         wait_queue_head_t config_change;
  36
  37         /* The thread servicing the balloon. */
  38         struct task_struct *thread;
  39
  40         /* Waiting for host to ack the pages we released. */
  41         struct completion acked;
  42
  43         /* Do we have to tell Host *before* we reuse pages? */
  44         bool tell_host_first;
  45
  46         /* The pages we've told the Host we're not using. */
  47         unsigned int num_pages;
  48         struct list_head pages;
  49
  50         /* The array of pfns we tell the Host about. */
  51         unsigned int num_pfns;
  52         u32 pfns[256];
  53
  54         /* Memory statistics */
  55         int need_stats_update;
  56         struct virtio_balloon_stat stats[VIRTIO_BALLOON_S_NR];
  57 };
  58
  59 static struct virtio_device_id id_table[] = {
  60         { VIRTIO_ID_BALLOON, VIRTIO_DEV_ANY_ID },
  61         { 0 },
  62 };
  63
  64 static u32 page_to_balloon_pfn(struct page *page)
  65 {
  66         unsigned long pfn = page_to_pfn(page);
  67
  68         BUILD_BUG_ON(PAGE_SHIFT < VIRTIO_BALLOON_PFN_SHIFT);
  69         /* Convert pfn from Linux page size to balloon page size. */
  70         return pfn >> (PAGE_SHIFT - VIRTIO_BALLOON_PFN_SHIFT);
  71 }
  72
  73 static void balloon_ack(struct virtqueue *vq)
  74 {
  75         struct virtio_balloon *vb;
  76         unsigned int len;
  77
  78         vb = vq->vq_ops->get_buf(vq, &len);
  79         if (vb)
  80                 complete(&vb->acked);
  81 }
  82
  83 static void tell_host(struct virtio_balloon *vb, struct virtqueue *vq)
  84 {
  85         struct scatterlist sg;
  86
  87         sg_init_one(&sg, vb->pfns, sizeof(vb->pfns[0]) * vb->num_pfns);
  88
  89         init_completion(&vb->acked);
  90
  91         /* We should always be able to add one buffer to an empty queue. */
  92         if (vq->vq_ops->add_buf(vq, &sg, 1, 0, vb) < 0)
  93                 BUG();
  94         vq->vq_ops->kick(vq);
  95
  96         /* When host has read buffer, this completes via balloon_ack */
  97         wait_for_completion(&vb->acked);
  98 }
  99
 100 static void fill_balloon(struct virtio_balloon *vb, size_t num)
 101 {
 102         /* We can only do one array worth at a time. */
 103         num = min(num, ARRAY_SIZE(vb->pfns));
 104
 105         for (vb->num_pfns = 0; vb->num_pfns < num; vb->num_pfns++) {
 106                 struct page *page = alloc_page(GFP_HIGHUSER | __GFP_NORETRY |
 107                                         __GFP_NOMEMALLOC | __GFP_NOWARN);
 108                 if (!page) {
 109                         if (printk_ratelimit())
 110                                 dev_printk(KERN_INFO, &vb->vdev->dev,
 111                                            "Out of puff! Can't get %zu pages\n",
 112                                            num);
 113                         /* Sleep for at least 1/5 of a second before retry. */
 114                         msleep(200);
 115                         break;
 116                 }
 117                 vb->pfns[vb->num_pfns] = page_to_balloon_pfn(page);
 118                 totalram_pages--;
 119                 vb->num_pages++;
 120                 list_add(&page->lru, &vb->pages);
 121         }
 122
 123         /* Didn't get any?  Oh well. */
 124         if (vb->num_pfns == 0)
 125                 return;
 126
 127         tell_host(vb, vb->inflate_vq);
 128 }
 129
 130 static void release_pages_by_pfn(const u32 pfns[], unsigned int num)
 131 {
 132         unsigned int i;
 133
 134         for (i = 0; i < num; i++) {
 135                 __free_page(pfn_to_page(pfns[i]));
 136                 totalram_pages++;
 137         }
 138 }
 139
 140 static void leak_balloon(struct virtio_balloon *vb, size_t num)
 141 {
 142         struct page *page;
 143
 144         /* We can only do one array worth at a time. */
 145         num = min(num, ARRAY_SIZE(vb->pfns));
 146
 147         for (vb->num_pfns = 0; vb->num_pfns < num; vb->num_pfns++) {
 148                 page = list_first_entry(&vb->pages, struct page, lru);
 149                 list_del(&page->lru);
 150                 vb->pfns[vb->num_pfns] = page_to_balloon_pfn(page);
 151                 vb->num_pages--;
 152         }
 153
 154         if (vb->tell_host_first) {
 155                 tell_host(vb, vb->deflate_vq);
 156                 release_pages_by_pfn(vb->pfns, vb->num_pfns);
 157         } else {
 158                 release_pages_by_pfn(vb->pfns, vb->num_pfns);
 159                 tell_host(vb, vb->deflate_vq);
 160         }
 161 }
 162
 163 static inline void update_stat(struct virtio_balloon *vb, int idx,
 164                                u16 tag, u64 val)
 165 {
 166         BUG_ON(idx >= VIRTIO_BALLOON_S_NR);
 167         vb->stats[idx].tag = tag;
 168         vb->stats[idx].val = val;
 169 }
 170
 171 #define pages_to_bytes(x) ((u64)(x) << PAGE_SHIFT)
 172
 173 static void update_balloon_stats(struct virtio_balloon *vb)
 174 {
 175         unsigned long events[NR_VM_EVENT_ITEMS];
 176         struct sysinfo i;
 177         int idx = 0;
 178
 179         all_vm_events(events);
 180         si_meminfo(&i);
 181
 182         update_stat(vb, idx++, VIRTIO_BALLOON_S_SWAP_IN,
 183                                 pages_to_bytes(events[PSWPIN]));
 184         update_stat(vb, idx++, VIRTIO_BALLOON_S_SWAP_OUT,
 185                                 pages_to_bytes(events[PSWPOUT]));
 186         update_stat(vb, idx++, VIRTIO_BALLOON_S_MAJFLT, events[PGMAJFAULT]);
 187         update_stat(vb, idx++, VIRTIO_BALLOON_S_MINFLT, events[PGFAULT]);
 188         update_stat(vb, idx++, VIRTIO_BALLOON_S_MEMFREE,
 189                                 pages_to_bytes(i.freeram));
 190         update_stat(vb, idx++, VIRTIO_BALLOON_S_MEMTOT,
 191                                 pages_to_bytes(i.totalram));
 192 }
 193
 194 /*
 195  * While most virtqueues communicate guest-initiated requests to the hypervisor,
 196  * the stats queue operates in reverse.  The driver initializes the virtqueue
 197  * with a single buffer.  From that point forward, all conversations consist of
 198  * a hypervisor request (a call to this function) which directs us to refill
 199  * the virtqueue with a fresh stats buffer.  Since stats collection can sleep,
 200  * we notify our kthread which does the actual work via stats_handle_request().
 201  */
 202 static void stats_request(struct virtqueue *vq)
 203 {
 204         struct virtio_balloon *vb;
 205         unsigned int len;
 206
 207         vb = vq->vq_ops->get_buf(vq, &len);
 208         if (!vb)
 209                 return;
 210         vb->need_stats_update = 1;
 211         wake_up(&vb->config_change);
 212 }
 213
 214 static void stats_handle_request(struct virtio_balloon *vb)
 215 {
 216         struct virtqueue *vq;
 217         struct scatterlist sg;
 218
 219         vb->need_stats_update = 0;
 220         update_balloon_stats(vb);
 221
 222         vq = vb->stats_vq;
 223         sg_init_one(&sg, vb->stats, sizeof(vb->stats));
 224         if (vq->vq_ops->add_buf(vq, &sg, 1, 0, vb) < 0)
 225                 BUG();
 226         vq->vq_ops->kick(vq);
 227 }
 228
 229 static void virtballoon_changed(struct virtio_device *vdev)
 230 {
 231         struct virtio_balloon *vb = vdev->priv;
 232
 233         wake_up(&vb->config_change);
 234 }
 235
 236 static inline s64 towards_target(struct virtio_balloon *vb)
 237 {
 238         u32 v;
 239         vb->vdev->config->get(vb->vdev,
 240                               offsetof(struct virtio_balloon_config, num_pages),
 241                               &v, sizeof(v));
 242         return (s64)v - vb->num_pages;
 243 }
 244
 245 static void update_balloon_size(struct virtio_balloon *vb)
 246 {
 247         __le32 actual = cpu_to_le32(vb->num_pages);
 248
 249         vb->vdev->config->set(vb->vdev,
 250                               offsetof(struct virtio_balloon_config, actual),
 251                               &actual, sizeof(actual));
 252 }
 253
 254 static int balloon(void *_vballoon)
 255 {
 256         struct virtio_balloon *vb = _vballoon;
 257
 258         set_freezable();
 259         while (!kthread_should_stop()) {
 260                 s64 diff;
 261
 262                 try_to_freeze();
 263                 wait_event_interruptible(vb->config_change,
 264                                          (diff = towards_target(vb)) != 0
 265                                          || vb->need_stats_update
 266                                          || kthread_should_stop()
 267                                          || freezing(current));
 268                 if (vb->need_stats_update)
 269                         stats_handle_request(vb);
 270                 if (diff > 0)
 271                         fill_balloon(vb, diff);
 272                 else if (diff < 0)
 273                         leak_balloon(vb, -diff);
 274                 update_balloon_size(vb);
 275         }
 276         return 0;
 277 }
 278
 279 static int virtballoon_probe(struct virtio_device *vdev)
 280 {
 281         struct virtio_balloon *vb;
 282         struct virtqueue *vqs[3];
 283         vq_callback_t *callbacks[] = { balloon_ack, balloon_ack, stats_request };
 284         const char *names[] = { "inflate", "deflate", "stats" };
 285         int err, nvqs;
 286
 287         vdev->priv = vb = kmalloc(sizeof(*vb), GFP_KERNEL);
 288         if (!vb) {
 289                 err = -ENOMEM;
 290                 goto out;
 291         }
 292
 293         INIT_LIST_HEAD(&vb->pages);
 294         vb->num_pages = 0;
 295         init_waitqueue_head(&vb->config_change);
 296         vb->vdev = vdev;
 297         vb->need_stats_update = 0;
 298
 299         /* We expect two virtqueues: inflate and deflate,
 300          * and optionally stat. */
 301         nvqs = virtio_has_feature(vb->vdev, VIRTIO_BALLOON_F_STATS_VQ) ? 3 : 2;
 302         err = vdev->config->find_vqs(vdev, nvqs, vqs, callbacks, names);
 303         if (err)
 304                 goto out_free_vb;
 305
 306         vb->inflate_vq = vqs[0];
 307         vb->deflate_vq = vqs[1];
 308         if (virtio_has_feature(vb->vdev, VIRTIO_BALLOON_F_STATS_VQ)) {
 309                 struct scatterlist sg;
 310                 vb->stats_vq = vqs[2];
 311
 312                 /*
 313                  * Prime this virtqueue with one buffer so the hypervisor can
 314                  * use it to signal us later.
 315                  */
 316                 sg_init_one(&sg, vb->stats, sizeof vb->stats);
 317                 if (vb->stats_vq->vq_ops->add_buf(vb->stats_vq,
 318                                                   &sg, 1, 0, vb) < 0)
 319                         BUG();
 320                 vb->stats_vq->vq_ops->kick(vb->stats_vq);
 321         }
 322
 323         vb->thread = kthread_run(balloon, vb, "vballoon");
 324         if (IS_ERR(vb->thread)) {
 325                 err = PTR_ERR(vb->thread);
 326                 goto out_del_vqs;
 327         }
 328
 329         vb->tell_host_first
 330                 = virtio_has_feature(vdev, VIRTIO_BALLOON_F_MUST_TELL_HOST);
 331
 332         return 0;
 333
 334 out_del_vqs:
 335         vdev->config->del_vqs(vdev);
 336 out_free_vb:
 337         kfree(vb);
 338 out:
 339         return err;
 340 }
 341
 342 static void __devexit virtballoon_remove(struct virtio_device *vdev)
 343 {
 344         struct virtio_balloon *vb = vdev->priv;
 345
 346         kthread_stop(vb->thread);
 347
 348         /* There might be pages left in the balloon: free them. */
 349         while (vb->num_pages)
 350                 leak_balloon(vb, vb->num_pages);
 351
 352         /* Now we reset the device so we can clean up the queues. */
 353         vdev->config->reset(vdev);
 354
 355         vdev->config->del_vqs(vdev);
 356         kfree(vb);
 357 }
 358
 359 static unsigned int features[] = {
 360         VIRTIO_BALLOON_F_MUST_TELL_HOST,
 361         VIRTIO_BALLOON_F_STATS_VQ,
 362 };
 363
 364 static struct virtio_driver virtio_balloon_driver = {
 365         .feature_table = features,
 366         .feature_table_size = ARRAY_SIZE(features),
 367         .driver.name =  KBUILD_MODNAME,
 368         .driver.owner = THIS_MODULE,
 369         .id_table =     id_table,
 370         .probe =        virtballoon_probe,
 371         .remove =       __devexit_p(virtballoon_remove),
 372         .config_changed = virtballoon_changed,
 373 };
 374
 375 static int __init init(void)
 376 {
 377         return register_virtio_driver(&virtio_balloon_driver);
 378 }
 379
 380 static void __exit fini(void)
 381 {
 382         unregister_virtio_driver(&virtio_balloon_driver);
 383 }
 384 module_init(init);
 385 module_exit(fini);
 386
 387 MODULE_DEVICE_TABLE(virtio, id_table);
 388 MODULE_DESCRIPTION("Virtio balloon driver");
 389 MODULE_LICENSE("GPL");