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_ids.h>
  23 #include <linux/virtio_balloon.h>
  24 #include <linux/swap.h>
  25 #include <linux/kthread.h>
  26 #include <linux/freezer.h>
  27 #include <linux/delay.h>
  28
  29 struct virtio_balloon
  30 {
  31         struct virtio_device *vdev;
  32         struct virtqueue *inflate_vq, *deflate_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
  55 static struct virtio_device_id id_table[] = {
  56         { VIRTIO_ID_BALLOON, VIRTIO_DEV_ANY_ID },
  57         { 0 },
  58 };
  59
  60 static u32 page_to_balloon_pfn(struct page *page)
  61 {
  62         unsigned long pfn = page_to_pfn(page);
  63
  64         BUILD_BUG_ON(PAGE_SHIFT < VIRTIO_BALLOON_PFN_SHIFT);
  65         /* Convert pfn from Linux page size to balloon page size. */
  66         return pfn >> (PAGE_SHIFT - VIRTIO_BALLOON_PFN_SHIFT);
  67 }
  68
  69 static void balloon_ack(struct virtqueue *vq)
  70 {
  71         struct virtio_balloon *vb;
  72         unsigned int len;
  73
  74         vb = vq->vq_ops->get_buf(vq, &len);
  75         if (vb)
  76                 complete(&vb->acked);
  77 }
  78
  79 static void tell_host(struct virtio_balloon *vb, struct virtqueue *vq)
  80 {
  81         struct scatterlist sg;
  82
  83         sg_init_one(&sg, vb->pfns, sizeof(vb->pfns[0]) * vb->num_pfns);
  84
  85         init_completion(&vb->acked);
  86
  87         /* We should always be able to add one buffer to an empty queue. */
  88         if (vq->vq_ops->add_buf(vq, &sg, 1, 0, vb) < 0)
  89                 BUG();
  90         vq->vq_ops->kick(vq);
  91
  92         /* When host has read buffer, this completes via balloon_ack */
  93         wait_for_completion(&vb->acked);
  94 }
  95
  96 static void fill_balloon(struct virtio_balloon *vb, size_t num)
  97 {
  98         /* We can only do one array worth at a time. */
  99         num = min(num, ARRAY_SIZE(vb->pfns));
 100
 101         for (vb->num_pfns = 0; vb->num_pfns < num; vb->num_pfns++) {
 102                 struct page *page = alloc_page(GFP_HIGHUSER | __GFP_NORETRY);
 103                 if (!page) {
 104                         if (printk_ratelimit())
 105                                 dev_printk(KERN_INFO, &vb->vdev->dev,
 106                                            "Out of puff! Can't get %zu pages\n",
 107                                            num);
 108                         /* Sleep for at least 1/5 of a second before retry. */
 109                         msleep(200);
 110                         break;
 111                 }
 112                 vb->pfns[vb->num_pfns] = page_to_balloon_pfn(page);
 113                 totalram_pages--;
 114                 vb->num_pages++;
 115                 list_add(&page->lru, &vb->pages);
 116         }
 117
 118         /* Didn't get any?  Oh well. */
 119         if (vb->num_pfns == 0)
 120                 return;
 121
 122         tell_host(vb, vb->inflate_vq);
 123 }
 124
 125 static void release_pages_by_pfn(const u32 pfns[], unsigned int num)
 126 {
 127         unsigned int i;
 128
 129         for (i = 0; i < num; i++) {
 130                 __free_page(pfn_to_page(pfns[i]));
 131                 totalram_pages++;
 132         }
 133 }
 134
 135 static void leak_balloon(struct virtio_balloon *vb, size_t num)
 136 {
 137         struct page *page;
 138
 139         /* We can only do one array worth at a time. */
 140         num = min(num, ARRAY_SIZE(vb->pfns));
 141
 142         for (vb->num_pfns = 0; vb->num_pfns < num; vb->num_pfns++) {
 143                 page = list_first_entry(&vb->pages, struct page, lru);
 144                 list_del(&page->lru);
 145                 vb->pfns[vb->num_pfns] = page_to_balloon_pfn(page);
 146                 vb->num_pages--;
 147         }
 148
 149         if (vb->tell_host_first) {
 150                 tell_host(vb, vb->deflate_vq);
 151                 release_pages_by_pfn(vb->pfns, vb->num_pfns);
 152         } else {
 153                 release_pages_by_pfn(vb->pfns, vb->num_pfns);
 154                 tell_host(vb, vb->deflate_vq);
 155         }
 156 }
 157
 158 static void virtballoon_changed(struct virtio_device *vdev)
 159 {
 160         struct virtio_balloon *vb = vdev->priv;
 161
 162         wake_up(&vb->config_change);
 163 }
 164
 165 static inline s64 towards_target(struct virtio_balloon *vb)
 166 {
 167         u32 v;
 168         vb->vdev->config->get(vb->vdev,
 169                               offsetof(struct virtio_balloon_config, num_pages),
 170                               &v, sizeof(v));
 171         return (s64)v - vb->num_pages;
 172 }
 173
 174 static void update_balloon_size(struct virtio_balloon *vb)
 175 {
 176         __le32 actual = cpu_to_le32(vb->num_pages);
 177
 178         vb->vdev->config->set(vb->vdev,
 179                               offsetof(struct virtio_balloon_config, actual),
 180                               &actual, sizeof(actual));
 181 }
 182
 183 static int balloon(void *_vballoon)
 184 {
 185         struct virtio_balloon *vb = _vballoon;
 186
 187         set_freezable();
 188         while (!kthread_should_stop()) {
 189                 s64 diff;
 190
 191                 try_to_freeze();
 192                 wait_event_interruptible(vb->config_change,
 193                                          (diff = towards_target(vb)) != 0
 194                                          || kthread_should_stop()
 195                                          || freezing(current));
 196                 if (diff > 0)
 197                         fill_balloon(vb, diff);
 198                 else if (diff < 0)
 199                         leak_balloon(vb, -diff);
 200                 update_balloon_size(vb);
 201         }
 202         return 0;
 203 }
 204
 205 static int virtballoon_probe(struct virtio_device *vdev)
 206 {
 207         struct virtio_balloon *vb;
 208         struct virtqueue *vqs[2];
 209         vq_callback_t *callbacks[] = { balloon_ack, balloon_ack };
 210         const char *names[] = { "inflate", "deflate" };
 211         int err;
 212
 213         vdev->priv = vb = kmalloc(sizeof(*vb), GFP_KERNEL);
 214         if (!vb) {
 215                 err = -ENOMEM;
 216                 goto out;
 217         }
 218
 219         INIT_LIST_HEAD(&vb->pages);
 220         vb->num_pages = 0;
 221         init_waitqueue_head(&vb->config_change);
 222         vb->vdev = vdev;
 223
 224         /* We expect two virtqueues. */
 225         err = vdev->config->find_vqs(vdev, 2, vqs, callbacks, names);
 226         if (err)
 227                 goto out_free_vb;
 228
 229         vb->inflate_vq = vqs[0];
 230         vb->deflate_vq = vqs[1];
 231
 232         vb->thread = kthread_run(balloon, vb, "vballoon");
 233         if (IS_ERR(vb->thread)) {
 234                 err = PTR_ERR(vb->thread);
 235                 goto out_del_vqs;
 236         }
 237
 238         vb->tell_host_first
 239                 = virtio_has_feature(vdev, VIRTIO_BALLOON_F_MUST_TELL_HOST);
 240
 241         return 0;
 242
 243 out_del_vqs:
 244         vdev->config->del_vqs(vdev);
 245 out_free_vb:
 246         kfree(vb);
 247 out:
 248         return err;
 249 }
 250
 251 static void virtballoon_remove(struct virtio_device *vdev)
 252 {
 253         struct virtio_balloon *vb = vdev->priv;
 254
 255         kthread_stop(vb->thread);
 256
 257         /* There might be pages left in the balloon: free them. */
 258         while (vb->num_pages)
 259                 leak_balloon(vb, vb->num_pages);
 260
 261         /* Now we reset the device so we can clean up the queues. */
 262         vdev->config->reset(vdev);
 263
 264         vdev->config->del_vqs(vdev);
 265         kfree(vb);
 266 }
 267
 268 static unsigned int features[] = { VIRTIO_BALLOON_F_MUST_TELL_HOST };
 269
 270 static struct virtio_driver virtio_balloon = {
 271         .feature_table = features,
 272         .feature_table_size = ARRAY_SIZE(features),
 273         .driver.name =  KBUILD_MODNAME,
 274         .driver.owner = THIS_MODULE,
 275         .id_table =     id_table,
 276         .probe =        virtballoon_probe,
 277         .remove =       __devexit_p(virtballoon_remove),
 278         .config_changed = virtballoon_changed,
 279 };
 280
 281 static int __init init(void)
 282 {
 283         return register_virtio_driver(&virtio_balloon);
 284 }
 285
 286 static void __exit fini(void)
 287 {
 288         unregister_virtio_driver(&virtio_balloon);
 289 }
 290 module_init(init);
 291 module_exit(fini);
 292
 293 MODULE_DEVICE_TABLE(virtio, id_table);
 294 MODULE_DESCRIPTION("Virtio balloon driver");
 295 MODULE_LICENSE("GPL");