linux/drivers/virtio/virtio_balloon.c
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   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
  28struct 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
  54static struct virtio_device_id id_table[] = {
  55        { VIRTIO_ID_BALLOON, VIRTIO_DEV_ANY_ID },
  56        { 0 },
  57};
  58
  59static 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
  69static 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
  86static 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
 115static 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
 125static 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
 148static void virtballoon_changed(struct virtio_device *vdev)
 149{
 150        struct virtio_balloon *vb = vdev->priv;
 151
 152        wake_up(&vb->config_change);
 153}
 154
 155static inline s64 towards_target(struct virtio_balloon *vb)
 156{
 157        u32 v;
 158        vb->vdev->config->get(vb->vdev,
 159                              offsetof(struct virtio_balloon_config, num_pages),
 160                              &v, sizeof(v));
 161        return (s64)v - vb->num_pages;
 162}
 163
 164static 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
 173static int balloon(void *_vballoon)
 174{
 175        struct virtio_balloon *vb = _vballoon;
 176
 177        set_freezable();
 178        while (!kthread_should_stop()) {
 179                s64 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
 194static 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                = virtio_has_feature(vdev, VIRTIO_BALLOON_F_MUST_TELL_HOST);
 231
 232        return 0;
 233
 234out_del_deflate_vq:
 235        vdev->config->del_vq(vb->deflate_vq);
 236out_del_inflate_vq:
 237        vdev->config->del_vq(vb->inflate_vq);
 238out_free_vb:
 239        kfree(vb);
 240out:
 241        return err;
 242}
 243
 244static 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
 262static unsigned int features[] = { VIRTIO_BALLOON_F_MUST_TELL_HOST };
 263
 264static struct virtio_driver virtio_balloon = {
 265        .feature_table = features,
 266        .feature_table_size = ARRAY_SIZE(features),
 267        .driver.name =  KBUILD_MODNAME,
 268        .driver.owner = THIS_MODULE,
 269        .id_table =     id_table,
 270        .probe =        virtballoon_probe,
 271        .remove =       __devexit_p(virtballoon_remove),
 272        .config_changed = virtballoon_changed,
 273};
 274
 275static int __init init(void)
 276{
 277        return register_virtio_driver(&virtio_balloon);
 278}
 279
 280static void __exit fini(void)
 281{
 282        unregister_virtio_driver(&virtio_balloon);
 283}
 284module_init(init);
 285module_exit(fini);
 286
 287MODULE_DEVICE_TABLE(virtio, id_table);
 288MODULE_DESCRIPTION("Virtio balloon driver");
 289MODULE_LICENSE("GPL");
 290
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