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 u32 page_to_balloon_pfn(struct page *page)
  60 {
  61         unsigned long pfn = page_to_pfn(page);
  62
  63         BUILD_BUG_ON(PAGE_SHIFT < VIRTIO_BALLOON_PFN_SHIFT);
  64         /* Convert pfn from Linux page size to balloon page size. */
  65         return pfn >> (PAGE_SHIFT - VIRTIO_BALLOON_PFN_SHIFT);
  66 }
  67
  68 static void balloon_ack(struct virtqueue *vq)
  69 {
  70         struct virtio_balloon *vb;
  71         unsigned int len;
  72
  73         vb = vq->vq_ops->get_buf(vq, &len);
  74         if (vb)
  75                 complete(&vb->acked);
  76 }
  77
  78 static void tell_host(struct virtio_balloon *vb, struct virtqueue *vq)
  79 {
  80         struct scatterlist sg;
  81
  82         sg_init_one(&sg, vb->pfns, sizeof(vb->pfns[0]) * vb->num_pfns);
  83
  84         init_completion(&vb->acked);
  85
  86         /* We should always be able to add one buffer to an empty queue. */
  87         if (vq->vq_ops->add_buf(vq, &sg, 1, 0, vb) < 0)
  88                 BUG();
  89         vq->vq_ops->kick(vq);
  90
  91         /* When host has read buffer, this completes via balloon_ack */
  92         wait_for_completion(&vb->acked);
  93 }
  94
  95 static void fill_balloon(struct virtio_balloon *vb, size_t num)
  96 {
  97         /* We can only do one array worth at a time. */
  98         num = min(num, ARRAY_SIZE(vb->pfns));
  99
 100         for (vb->num_pfns = 0; vb->num_pfns < num; vb->num_pfns++) {
 101                 struct page *page = alloc_page(GFP_HIGHUSER | __GFP_NORETRY);
 102                 if (!page) {
 103                         if (printk_ratelimit())
 104                                 dev_printk(KERN_INFO, &vb->vdev->dev,
 105                                            "Out of puff! Can't get %zu pages\n",
 106                                            num);
 107                         /* Sleep for at least 1/5 of a second before retry. */
 108                         msleep(200);
 109                         break;
 110                 }
 111                 vb->pfns[vb->num_pfns] = page_to_balloon_pfn(page);
 112                 totalram_pages--;
 113                 vb->num_pages++;
 114                 list_add(&page->lru, &vb->pages);
 115         }
 116
 117         /* Didn't get any?  Oh well. */
 118         if (vb->num_pfns == 0)
 119                 return;
 120
 121         tell_host(vb, vb->inflate_vq);
 122 }
 123
 124 static void release_pages_by_pfn(const u32 pfns[], unsigned int num)
 125 {
 126         unsigned int i;
 127
 128         for (i = 0; i < num; i++) {
 129                 __free_page(pfn_to_page(pfns[i]));
 130                 totalram_pages++;
 131         }
 132 }
 133
 134 static void leak_balloon(struct virtio_balloon *vb, size_t num)
 135 {
 136         struct page *page;
 137
 138         /* We can only do one array worth at a time. */
 139         num = min(num, ARRAY_SIZE(vb->pfns));
 140
 141         for (vb->num_pfns = 0; vb->num_pfns < num; vb->num_pfns++) {
 142                 page = list_first_entry(&vb->pages, struct page, lru);
 143                 list_del(&page->lru);
 144                 vb->pfns[vb->num_pfns] = page_to_balloon_pfn(page);
 145                 vb->num_pages--;
 146         }
 147
 148         if (vb->tell_host_first) {
 149                 tell_host(vb, vb->deflate_vq);
 150                 release_pages_by_pfn(vb->pfns, vb->num_pfns);
 151         } else {
 152                 release_pages_by_pfn(vb->pfns, vb->num_pfns);
 153                 tell_host(vb, vb->deflate_vq);
 154         }
 155 }
 156
 157 static void virtballoon_changed(struct virtio_device *vdev)
 158 {
 159         struct virtio_balloon *vb = vdev->priv;
 160
 161         wake_up(&vb->config_change);
 162 }
 163
 164 static inline s64 towards_target(struct virtio_balloon *vb)
 165 {
 166         u32 v;
 167         vb->vdev->config->get(vb->vdev,
 168                               offsetof(struct virtio_balloon_config, num_pages),
 169                               &v, sizeof(v));
 170         return (s64)v - vb->num_pages;
 171 }
 172
 173 static void update_balloon_size(struct virtio_balloon *vb)
 174 {
 175         __le32 actual = cpu_to_le32(vb->num_pages);
 176
 177         vb->vdev->config->set(vb->vdev,
 178                               offsetof(struct virtio_balloon_config, actual),
 179                               &actual, sizeof(actual));
 180 }
 181
 182 static int balloon(void *_vballoon)
 183 {
 184         struct virtio_balloon *vb = _vballoon;
 185
 186         set_freezable();
 187         while (!kthread_should_stop()) {
 188                 s64 diff;
 189
 190                 try_to_freeze();
 191                 wait_event_interruptible(vb->config_change,
 192                                          (diff = towards_target(vb)) != 0
 193                                          || kthread_should_stop()
 194                                          || freezing(current));
 195                 if (diff > 0)
 196                         fill_balloon(vb, diff);
 197                 else if (diff < 0)
 198                         leak_balloon(vb, -diff);
 199                 update_balloon_size(vb);
 200         }
 201         return 0;
 202 }
 203
 204 static int virtballoon_probe(struct virtio_device *vdev)
 205 {
 206         struct virtio_balloon *vb;
 207         struct virtqueue *vqs[2];
 208         vq_callback_t *callbacks[] = { balloon_ack, balloon_ack };
 209         const char *names[] = { "inflate", "deflate" };
 210         int err;
 211
 212         vdev->priv = vb = kmalloc(sizeof(*vb), GFP_KERNEL);
 213         if (!vb) {
 214                 err = -ENOMEM;
 215                 goto out;
 216         }
 217
 218         INIT_LIST_HEAD(&vb->pages);
 219         vb->num_pages = 0;
 220         init_waitqueue_head(&vb->config_change);
 221         vb->vdev = vdev;
 222
 223         /* We expect two virtqueues. */
 224         err = vdev->config->find_vqs(vdev, 2, vqs, callbacks, names);
 225         if (err)
 226                 goto out_free_vb;
 227
 228         vb->inflate_vq = vqs[0];
 229         vb->deflate_vq = vqs[1];
 230
 231         vb->thread = kthread_run(balloon, vb, "vballoon");
 232         if (IS_ERR(vb->thread)) {
 233                 err = PTR_ERR(vb->thread);
 234                 goto out_del_vqs;
 235         }
 236
 237         vb->tell_host_first
 238                 = virtio_has_feature(vdev, VIRTIO_BALLOON_F_MUST_TELL_HOST);
 239
 240         return 0;
 241
 242 out_del_vqs:
 243         vdev->config->del_vqs(vdev);
 244 out_free_vb:
 245         kfree(vb);
 246 out:
 247         return err;
 248 }
 249
 250 static void virtballoon_remove(struct virtio_device *vdev)
 251 {
 252         struct virtio_balloon *vb = vdev->priv;
 253
 254         kthread_stop(vb->thread);
 255
 256         /* There might be pages left in the balloon: free them. */
 257         while (vb->num_pages)
 258                 leak_balloon(vb, vb->num_pages);
 259
 260         /* Now we reset the device so we can clean up the queues. */
 261         vdev->config->reset(vdev);
 262
 263         vdev->config->del_vqs(vdev);
 264         kfree(vb);
 265 }
 266
 267 static unsigned int features[] = { VIRTIO_BALLOON_F_MUST_TELL_HOST };
 268
 269 static struct virtio_driver virtio_balloon = {
 270         .feature_table = features,
 271         .feature_table_size = ARRAY_SIZE(features),
 272         .driver.name =  KBUILD_MODNAME,
 273         .driver.owner = THIS_MODULE,
 274         .id_table =     id_table,
 275         .probe =        virtballoon_probe,
 276         .remove =       __devexit_p(virtballoon_remove),
 277         .config_changed = virtballoon_changed,
 278 };
 279
 280 static int __init init(void)
 281 {
 282         return register_virtio_driver(&virtio_balloon);
 283 }
 284
 285 static void __exit fini(void)
 286 {
 287         unregister_virtio_driver(&virtio_balloon);
 288 }
 289 module_init(init);
 290 module_exit(fini);
 291
 292 MODULE_DEVICE_TABLE(virtio, id_table);
 293 MODULE_DESCRIPTION("Virtio balloon driver");
 294 MODULE_LICENSE("GPL");