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                 if (!page) {
 108                         if (printk_ratelimit())
 109                                 dev_printk(KERN_INFO, &vb->vdev->dev,
 110                                            "Out of puff! Can't get %zu pages\n",
 111                                            num);
 112                         /* Sleep for at least 1/5 of a second before retry. */
 113                         msleep(200);
 114                         break;
 115                 }
 116                 vb->pfns[vb->num_pfns] = page_to_balloon_pfn(page);
 117                 totalram_pages--;
 118                 vb->num_pages++;
 119                 list_add(&page->lru, &vb->pages);
 120         }
 121
 122         /* Didn't get any?  Oh well. */
 123         if (vb->num_pfns == 0)
 124                 return;
 125
 126         tell_host(vb, vb->inflate_vq);
 127 }
 128
 129 static void release_pages_by_pfn(const u32 pfns[], unsigned int num)
 130 {
 131         unsigned int i;
 132
 133         for (i = 0; i < num; i++) {
 134                 __free_page(pfn_to_page(pfns[i]));
 135                 totalram_pages++;
 136         }
 137 }
 138
 139 static void leak_balloon(struct virtio_balloon *vb, size_t num)
 140 {
 141         struct page *page;
 142
 143         /* We can only do one array worth at a time. */
 144         num = min(num, ARRAY_SIZE(vb->pfns));
 145
 146         for (vb->num_pfns = 0; vb->num_pfns < num; vb->num_pfns++) {
 147                 page = list_first_entry(&vb->pages, struct page, lru);
 148                 list_del(&page->lru);
 149                 vb->pfns[vb->num_pfns] = page_to_balloon_pfn(page);
 150                 vb->num_pages--;
 151         }
 152
 153         if (vb->tell_host_first) {
 154                 tell_host(vb, vb->deflate_vq);
 155                 release_pages_by_pfn(vb->pfns, vb->num_pfns);
 156         } else {
 157                 release_pages_by_pfn(vb->pfns, vb->num_pfns);
 158                 tell_host(vb, vb->deflate_vq);
 159         }
 160 }
 161
 162 static inline void update_stat(struct virtio_balloon *vb, int idx,
 163                                u16 tag, u64 val)
 164 {
 165         BUG_ON(idx >= VIRTIO_BALLOON_S_NR);
 166         vb->stats[idx].tag = tag;
 167         vb->stats[idx].val = val;
 168 }
 169
 170 #define pages_to_bytes(x) ((u64)(x) << PAGE_SHIFT)
 171
 172 static void update_balloon_stats(struct virtio_balloon *vb)
 173 {
 174         unsigned long events[NR_VM_EVENT_ITEMS];
 175         struct sysinfo i;
 176         int idx = 0;
 177
 178         all_vm_events(events);
 179         si_meminfo(&i);
 180
 181         update_stat(vb, idx++, VIRTIO_BALLOON_S_SWAP_IN,
 182                                 pages_to_bytes(events[PSWPIN]));
 183         update_stat(vb, idx++, VIRTIO_BALLOON_S_SWAP_OUT,
 184                                 pages_to_bytes(events[PSWPOUT]));
 185         update_stat(vb, idx++, VIRTIO_BALLOON_S_MAJFLT, events[PGMAJFAULT]);
 186         update_stat(vb, idx++, VIRTIO_BALLOON_S_MINFLT, events[PGFAULT]);
 187         update_stat(vb, idx++, VIRTIO_BALLOON_S_MEMFREE,
 188                                 pages_to_bytes(i.freeram));
 189         update_stat(vb, idx++, VIRTIO_BALLOON_S_MEMTOT,
 190                                 pages_to_bytes(i.totalram));
 191 }
 192
 193 /*
 194  * While most virtqueues communicate guest-initiated requests to the hypervisor,
 195  * the stats queue operates in reverse.  The driver initializes the virtqueue
 196  * with a single buffer.  From that point forward, all conversations consist of
 197  * a hypervisor request (a call to this function) which directs us to refill
 198  * the virtqueue with a fresh stats buffer.  Since stats collection can sleep,
 199  * we notify our kthread which does the actual work via stats_handle_request().
 200  */
 201 static void stats_request(struct virtqueue *vq)
 202 {
 203         struct virtio_balloon *vb;
 204         unsigned int len;
 205
 206         vb = vq->vq_ops->get_buf(vq, &len);
 207         if (!vb)
 208                 return;
 209         vb->need_stats_update = 1;
 210         wake_up(&vb->config_change);
 211 }
 212
 213 static void stats_handle_request(struct virtio_balloon *vb)
 214 {
 215         struct virtqueue *vq;
 216         struct scatterlist sg;
 217
 218         vb->need_stats_update = 0;
 219         update_balloon_stats(vb);
 220
 221         vq = vb->stats_vq;
 222         sg_init_one(&sg, vb->stats, sizeof(vb->stats));
 223         if (vq->vq_ops->add_buf(vq, &sg, 1, 0, vb) < 0)
 224                 BUG();
 225         vq->vq_ops->kick(vq);
 226 }
 227
 228 static void virtballoon_changed(struct virtio_device *vdev)
 229 {
 230         struct virtio_balloon *vb = vdev->priv;
 231
 232         wake_up(&vb->config_change);
 233 }
 234
 235 static inline s64 towards_target(struct virtio_balloon *vb)
 236 {
 237         u32 v;
 238         vb->vdev->config->get(vb->vdev,
 239                               offsetof(struct virtio_balloon_config, num_pages),
 240                               &v, sizeof(v));
 241         return (s64)v - vb->num_pages;
 242 }
 243
 244 static void update_balloon_size(struct virtio_balloon *vb)
 245 {
 246         __le32 actual = cpu_to_le32(vb->num_pages);
 247
 248         vb->vdev->config->set(vb->vdev,
 249                               offsetof(struct virtio_balloon_config, actual),
 250                               &actual, sizeof(actual));
 251 }
 252
 253 static int balloon(void *_vballoon)
 254 {
 255         struct virtio_balloon *vb = _vballoon;
 256
 257         set_freezable();
 258         while (!kthread_should_stop()) {
 259                 s64 diff;
 260
 261                 try_to_freeze();
 262                 wait_event_interruptible(vb->config_change,
 263                                          (diff = towards_target(vb)) != 0
 264                                          || vb->need_stats_update
 265                                          || kthread_should_stop()
 266                                          || freezing(current));
 267                 if (vb->need_stats_update)
 268                         stats_handle_request(vb);
 269                 if (diff > 0)
 270                         fill_balloon(vb, diff);
 271                 else if (diff < 0)
 272                         leak_balloon(vb, -diff);
 273                 update_balloon_size(vb);
 274         }
 275         return 0;
 276 }
 277
 278 static int virtballoon_probe(struct virtio_device *vdev)
 279 {
 280         struct virtio_balloon *vb;
 281         struct virtqueue *vqs[3];
 282         vq_callback_t *callbacks[] = { balloon_ack, balloon_ack, stats_request };
 283         const char *names[] = { "inflate", "deflate", "stats" };
 284         int err, nvqs;
 285
 286         vdev->priv = vb = kmalloc(sizeof(*vb), GFP_KERNEL);
 287         if (!vb) {
 288                 err = -ENOMEM;
 289                 goto out;
 290         }
 291
 292         INIT_LIST_HEAD(&vb->pages);
 293         vb->num_pages = 0;
 294         init_waitqueue_head(&vb->config_change);
 295         vb->vdev = vdev;
 296         vb->need_stats_update = 0;
 297
 298         /* We expect two virtqueues: inflate and deflate,
 299          * and optionally stat. */
 300         nvqs = virtio_has_feature(vb->vdev, VIRTIO_BALLOON_F_STATS_VQ) ? 3 : 2;
 301         err = vdev->config->find_vqs(vdev, nvqs, vqs, callbacks, names);
 302         if (err)
 303                 goto out_free_vb;
 304
 305         vb->inflate_vq = vqs[0];
 306         vb->deflate_vq = vqs[1];
 307         if (virtio_has_feature(vb->vdev, VIRTIO_BALLOON_F_STATS_VQ)) {
 308                 struct scatterlist sg;
 309                 vb->stats_vq = vqs[2];
 310
 311                 /*
 312                  * Prime this virtqueue with one buffer so the hypervisor can
 313                  * use it to signal us later.
 314                  */
 315                 sg_init_one(&sg, vb->stats, sizeof vb->stats);
 316                 if (vb->stats_vq->vq_ops->add_buf(vb->stats_vq,
 317                                                   &sg, 1, 0, vb) < 0)
 318                         BUG();
 319                 vb->stats_vq->vq_ops->kick(vb->stats_vq);
 320         }
 321
 322         vb->thread = kthread_run(balloon, vb, "vballoon");
 323         if (IS_ERR(vb->thread)) {
 324                 err = PTR_ERR(vb->thread);
 325                 goto out_del_vqs;
 326         }
 327
 328         vb->tell_host_first
 329                 = virtio_has_feature(vdev, VIRTIO_BALLOON_F_MUST_TELL_HOST);
 330
 331         return 0;
 332
 333 out_del_vqs:
 334         vdev->config->del_vqs(vdev);
 335 out_free_vb:
 336         kfree(vb);
 337 out:
 338         return err;
 339 }
 340
 341 static void __devexit virtballoon_remove(struct virtio_device *vdev)
 342 {
 343         struct virtio_balloon *vb = vdev->priv;
 344
 345         kthread_stop(vb->thread);
 346
 347         /* There might be pages left in the balloon: free them. */
 348         while (vb->num_pages)
 349                 leak_balloon(vb, vb->num_pages);
 350
 351         /* Now we reset the device so we can clean up the queues. */
 352         vdev->config->reset(vdev);
 353
 354         vdev->config->del_vqs(vdev);
 355         kfree(vb);
 356 }
 357
 358 static unsigned int features[] = {
 359         VIRTIO_BALLOON_F_MUST_TELL_HOST,
 360         VIRTIO_BALLOON_F_STATS_VQ,
 361 };
 362
 363 static struct virtio_driver virtio_balloon_driver = {
 364         .feature_table = features,
 365         .feature_table_size = ARRAY_SIZE(features),
 366         .driver.name =  KBUILD_MODNAME,
 367         .driver.owner = THIS_MODULE,
 368         .id_table =     id_table,
 369         .probe =        virtballoon_probe,
 370         .remove =       __devexit_p(virtballoon_remove),
 371         .config_changed = virtballoon_changed,
 372 };
 373
 374 static int __init init(void)
 375 {
 376         return register_virtio_driver(&virtio_balloon_driver);
 377 }
 378
 379 static void __exit fini(void)
 380 {
 381         unregister_virtio_driver(&virtio_balloon_driver);
 382 }
 383 module_init(init);
 384 module_exit(fini);
 385
 386 MODULE_DEVICE_TABLE(virtio, id_table);
 387 MODULE_DESCRIPTION("Virtio balloon driver");
 388 MODULE_LICENSE("GPL");