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
  28 struct virtio_balloon
  29 {
  30         struct virtio_device *vdev;
  31         struct virtqueue *inflate_vq, *deflate_vq;
  32
  33         /* Where the ballooning thread waits for config to change. */
  34         wait_queue_head_t config_change;
  35
  36         /* The thread servicing the balloon. */
  37         struct task_struct *thread;
  38
  39         /* Waiting for host to ack the pages we released. */
  40         struct completion acked;
  41
  42         /* Do we have to tell Host *before* we reuse pages? */
  43         bool tell_host_first;
  44
  45         /* The pages we've told the Host we're not using. */
  46         unsigned int num_pages;
  47         struct list_head pages;
  48
  49         /* The array of pfns we tell the Host about. */
  50         unsigned int num_pfns;
  51         u32 pfns[256];
  52 };
  53
  54 static struct virtio_device_id id_table[] = {
  55         { VIRTIO_ID_BALLOON, VIRTIO_DEV_ANY_ID },
  56         { 0 },
  57 };
  58
  59 static void balloon_ack(struct virtqueue *vq)
  60 {
  61         struct virtio_balloon *vb;
  62         unsigned int len;
  63
  64         vb = vq->vq_ops->get_buf(vq, &len);
  65         if (vb)
  66                 complete(&vb->acked);
  67 }
  68
  69 static void tell_host(struct virtio_balloon *vb, struct virtqueue *vq)
  70 {
  71         struct scatterlist sg;
  72
  73         sg_init_one(&sg, vb->pfns, sizeof(vb->pfns[0]) * vb->num_pfns);
  74
  75         init_completion(&vb->acked);
  76
  77         /* We should always be able to add one buffer to an empty queue. */
  78         if (vq->vq_ops->add_buf(vq, &sg, 1, 0, vb) != 0)
  79                 BUG();
  80         vq->vq_ops->kick(vq);
  81
  82         /* When host has read buffer, this completes via balloon_ack */
  83         wait_for_completion(&vb->acked);
  84 }
  85
  86 static void fill_balloon(struct virtio_balloon *vb, size_t num)
  87 {
  88         /* We can only do one array worth at a time. */
  89         num = min(num, ARRAY_SIZE(vb->pfns));
  90
  91         for (vb->num_pfns = 0; vb->num_pfns < num; vb->num_pfns++) {
  92                 struct page *page = alloc_page(GFP_HIGHUSER | __GFP_NORETRY);
  93                 if (!page) {
  94                         if (printk_ratelimit())
  95                                 dev_printk(KERN_INFO, &vb->vdev->dev,
  96                                            "Out of puff! Can't get %zu pages\n",
  97                                            num);
  98                         /* Sleep for at least 1/5 of a second before retry. */
  99                         msleep(200);
 100                         break;
 101                 }
 102                 vb->pfns[vb->num_pfns] = page_to_pfn(page);
 103                 totalram_pages--;
 104                 vb->num_pages++;
 105                 list_add(&page->lru, &vb->pages);
 106         }
 107
 108         /* Didn't get any?  Oh well. */
 109         if (vb->num_pfns == 0)
 110                 return;
 111
 112         tell_host(vb, vb->inflate_vq);
 113 }
 114
 115 static void release_pages_by_pfn(const u32 pfns[], unsigned int num)
 116 {
 117         unsigned int i;
 118
 119         for (i = 0; i < num; i++) {
 120                 __free_page(pfn_to_page(pfns[i]));
 121                 totalram_pages++;
 122         }
 123 }
 124
 125 static void leak_balloon(struct virtio_balloon *vb, size_t num)
 126 {
 127         struct page *page;
 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; vb->num_pfns++) {
 133                 page = list_first_entry(&vb->pages, struct page, lru);
 134                 list_del(&page->lru);
 135                 vb->pfns[vb->num_pfns] = page_to_pfn(page);
 136                 vb->num_pages--;
 137         }
 138
 139         if (vb->tell_host_first) {
 140                 tell_host(vb, vb->deflate_vq);
 141                 release_pages_by_pfn(vb->pfns, vb->num_pfns);
 142         } else {
 143                 release_pages_by_pfn(vb->pfns, vb->num_pfns);
 144                 tell_host(vb, vb->deflate_vq);
 145         }
 146 }
 147
 148 static void virtballoon_changed(struct virtio_device *vdev)
 149 {
 150         struct virtio_balloon *vb = vdev->priv;
 151
 152         wake_up(&vb->config_change);
 153 }
 154
 155 static inline int towards_target(struct virtio_balloon *vb)
 156 {
 157         u32 v;
 158         __virtio_config_val(vb->vdev,
 159                             offsetof(struct virtio_balloon_config, num_pages),
 160                             &v);
 161         return v - vb->num_pages;
 162 }
 163
 164 static void update_balloon_size(struct virtio_balloon *vb)
 165 {
 166         __le32 actual = cpu_to_le32(vb->num_pages);
 167
 168         vb->vdev->config->set(vb->vdev,
 169                               offsetof(struct virtio_balloon_config, actual),
 170                               &actual, sizeof(actual));
 171 }
 172
 173 static int balloon(void *_vballoon)
 174 {
 175         struct virtio_balloon *vb = _vballoon;
 176
 177         set_freezable();
 178         while (!kthread_should_stop()) {
 179                 int diff;
 180
 181                 try_to_freeze();
 182                 wait_event_interruptible(vb->config_change,
 183                                          (diff = towards_target(vb)) != 0
 184                                          || kthread_should_stop());
 185                 if (diff > 0)
 186                         fill_balloon(vb, diff);
 187                 else if (diff < 0)
 188                         leak_balloon(vb, -diff);
 189                 update_balloon_size(vb);
 190         }
 191         return 0;
 192 }
 193
 194 static int virtballoon_probe(struct virtio_device *vdev)
 195 {
 196         struct virtio_balloon *vb;
 197         int err;
 198
 199         vdev->priv = vb = kmalloc(sizeof(*vb), GFP_KERNEL);
 200         if (!vb) {
 201                 err = -ENOMEM;
 202                 goto out;
 203         }
 204
 205         INIT_LIST_HEAD(&vb->pages);
 206         vb->num_pages = 0;
 207         init_waitqueue_head(&vb->config_change);
 208         vb->vdev = vdev;
 209
 210         /* We expect two virtqueues. */
 211         vb->inflate_vq = vdev->config->find_vq(vdev, 0, balloon_ack);
 212         if (IS_ERR(vb->inflate_vq)) {
 213                 err = PTR_ERR(vb->inflate_vq);
 214                 goto out_free_vb;
 215         }
 216
 217         vb->deflate_vq = vdev->config->find_vq(vdev, 1, balloon_ack);
 218         if (IS_ERR(vb->deflate_vq)) {
 219                 err = PTR_ERR(vb->deflate_vq);
 220                 goto out_del_inflate_vq;
 221         }
 222
 223         vb->thread = kthread_run(balloon, vb, "vballoon");
 224         if (IS_ERR(vb->thread)) {
 225                 err = PTR_ERR(vb->thread);
 226                 goto out_del_deflate_vq;
 227         }
 228
 229         vb->tell_host_first
 230                 = vdev->config->feature(vdev, VIRTIO_BALLOON_F_MUST_TELL_HOST);
 231
 232         return 0;
 233
 234 out_del_deflate_vq:
 235         vdev->config->del_vq(vb->deflate_vq);
 236 out_del_inflate_vq:
 237         vdev->config->del_vq(vb->inflate_vq);
 238 out_free_vb:
 239         kfree(vb);
 240 out:
 241         return err;
 242 }
 243
 244 static void virtballoon_remove(struct virtio_device *vdev)
 245 {
 246         struct virtio_balloon *vb = vdev->priv;
 247
 248         kthread_stop(vb->thread);
 249
 250         /* There might be pages left in the balloon: free them. */
 251         while (vb->num_pages)
 252                 leak_balloon(vb, vb->num_pages);
 253
 254         /* Now we reset the device so we can clean up the queues. */
 255         vdev->config->reset(vdev);
 256
 257         vdev->config->del_vq(vb->deflate_vq);
 258         vdev->config->del_vq(vb->inflate_vq);
 259         kfree(vb);
 260 }
 261
 262 static struct virtio_driver virtio_balloon = {
 263         .driver.name =  KBUILD_MODNAME,
 264         .driver.owner = THIS_MODULE,
 265         .id_table =     id_table,
 266         .probe =        virtballoon_probe,
 267         .remove =       __devexit_p(virtballoon_remove),
 268         .config_changed = virtballoon_changed,
 269 };
 270
 271 static int __init init(void)
 272 {
 273         return register_virtio_driver(&virtio_balloon);
 274 }
 275
 276 static void __exit fini(void)
 277 {
 278         unregister_virtio_driver(&virtio_balloon);
 279 }
 280 module_init(init);
 281 module_exit(fini);
 282
 283 MODULE_DEVICE_TABLE(virtio, id_table);
 284 MODULE_DESCRIPTION("Virtio balloon driver");
 285 MODULE_LICENSE("GPL");