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