virtio_balloon.c

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/*
 * Virtio balloon implementation, inspired by Dor Laor and Marcelo
 * Tosatti's implementations.
 *
 *  Copyright 2008 Rusty Russell IBM Corporation
 *
 *  This program is free software; you can redistribute it and/or modify
 *  it under the terms of the GNU General Public License as published by
 *  the Free Software Foundation; either version 2 of the License, or
 *  (at your option) any later version.
 *
 *  This program is distributed in the hope that it will be useful,
 *  but WITHOUT ANY WARRANTY; without even the implied warranty of
 *  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 *  GNU General Public License for more details.
 *
 *  You should have received a copy of the GNU General Public License
 *  along with this program; if not, write to the Free Software
 *  Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA  02110-1301  USA
 */

#include <linux/virtio.h>
#include <linux/virtio_balloon.h>
#include <linux/swap.h>
#include <linux/kthread.h>
#include <linux/freezer.h>
#include <linux/delay.h>
#include <linux/slab.h>
#include <linux/module.h>

/*
 * Balloon device works in 4K page units.  So each page is pointed to by
 * multiple balloon pages.  All memory counters in this driver are in balloon
 * page units.
 */
#define VIRTIO_BALLOON_PAGES_PER_PAGE (PAGE_SIZE >> VIRTIO_BALLOON_PFN_SHIFT)

struct virtio_balloon
{
    struct virtio_device *vdev;
    struct virtqueue *inflate_vq, *deflate_vq, *stats_vq;

    /* Where the ballooning thread waits for config to change. */
    wait_queue_head_t config_change;

    /* The thread servicing the balloon. */
    struct task_struct *thread;

    /* Waiting for host to ack the pages we released. */
    wait_queue_head_t acked;

    /* Number of balloon pages we've told the Host we're not using. */
    unsigned int num_pages;
    /*
     * The pages we've told the Host we're not using.
     * Each page on this list adds VIRTIO_BALLOON_PAGES_PER_PAGE
     * to num_pages above.
     */
    struct list_head pages;

    /* The array of pfns we tell the Host about. */
    unsigned int num_pfns;
    u32 pfns[256];

    /* Memory statistics */
    int need_stats_update;
    struct virtio_balloon_stat stats[VIRTIO_BALLOON_S_NR];
};

static struct virtio_device_id id_table[] = {
    { VIRTIO_ID_BALLOON, VIRTIO_DEV_ANY_ID },
    { 0 },
};

static u32 page_to_balloon_pfn(struct page *page)
{
    unsigned long pfn = page_to_pfn(page);

    BUILD_BUG_ON(PAGE_SHIFT < VIRTIO_BALLOON_PFN_SHIFT);
    /* Convert pfn from Linux page size to balloon page size. */
    return pfn * VIRTIO_BALLOON_PAGES_PER_PAGE;
}

static struct page *balloon_pfn_to_page(u32 pfn)
{
    BUG_ON(pfn % VIRTIO_BALLOON_PAGES_PER_PAGE);
    return pfn_to_page(pfn / VIRTIO_BALLOON_PAGES_PER_PAGE);
}

static void balloon_ack(struct virtqueue *vq)
{
    struct virtio_balloon *vb = vq->vdev->priv;

    wake_up(&vb->acked);
}

static void tell_host(struct virtio_balloon *vb, struct virtqueue *vq)
{
    struct scatterlist sg;
    unsigned int len;

    sg_init_one(&sg, vb->pfns, sizeof(vb->pfns[0]) * vb->num_pfns);

    /* We should always be able to add one buffer to an empty queue. */
    if (virtqueue_add_buf(vq, &sg, 1, 0, vb, GFP_KERNEL) < 0)
        BUG();
    virtqueue_kick(vq);

    /* When host has read buffer, this completes via balloon_ack */
    wait_event(vb->acked, virtqueue_get_buf(vq, &len));
}

static void set_page_pfns(u32 pfns[], struct page *page)
{
    unsigned int i;

    /* Set balloon pfns pointing at this page.
     * Note that the first pfn points at start of the page. */
    for (i = 0; i < VIRTIO_BALLOON_PAGES_PER_PAGE; i++)
        pfns[i] = page_to_balloon_pfn(page) + i;
}

static void fill_balloon(struct virtio_balloon *vb, size_t num)
{
    /* We can only do one array worth at a time. */
    num = min(num, ARRAY_SIZE(vb->pfns));

    for (vb->num_pfns = 0; vb->num_pfns < num;
         vb->num_pfns += VIRTIO_BALLOON_PAGES_PER_PAGE) {
        struct page *page = alloc_page(GFP_HIGHUSER | __GFP_NORETRY |
                    __GFP_NOMEMALLOC | __GFP_NOWARN);
        if (!page) {
            if (printk_ratelimit())
                dev_printk(KERN_INFO, &vb->vdev->dev,
                       "Out of puff! Can't get %zu pages\n",
                       num);
            /* Sleep for at least 1/5 of a second before retry. */
            msleep(200);
            break;
        }
        set_page_pfns(vb->pfns + vb->num_pfns, page);
        vb->num_pages += VIRTIO_BALLOON_PAGES_PER_PAGE;
        totalram_pages--;
        list_add(&page->lru, &vb->pages);
    }

    /* Didn't get any?  Oh well. */
    if (vb->num_pfns == 0)
        return;

    tell_host(vb, vb->inflate_vq);
}

static void release_pages_by_pfn(const u32 pfns[], unsigned int num)
{
    unsigned int i;

    /* Find pfns pointing at start of each page, get pages and free them. */
    for (i = 0; i < num; i += VIRTIO_BALLOON_PAGES_PER_PAGE) {
        __free_page(balloon_pfn_to_page(pfns[i]));
        totalram_pages++;
    }
}

static void leak_balloon(struct virtio_balloon *vb, size_t num)
{
    struct page *page;

    /* We can only do one array worth at a time. */
    num = min(num, ARRAY_SIZE(vb->pfns));

    for (vb->num_pfns = 0; vb->num_pfns < num;
         vb->num_pfns += VIRTIO_BALLOON_PAGES_PER_PAGE) {
        page = list_first_entry(&vb->pages, struct page, lru);
        list_del(&page->lru);
        set_page_pfns(vb->pfns + vb->num_pfns, page);
        vb->num_pages -= VIRTIO_BALLOON_PAGES_PER_PAGE;
    }

    /*
     * Note that if
     * virtio_has_feature(vdev, VIRTIO_BALLOON_F_MUST_TELL_HOST);
     * is true, we *have* to do it in this order
     */
    tell_host(vb, vb->deflate_vq);
    release_pages_by_pfn(vb->pfns, vb->num_pfns);
}

static inline void update_stat(struct virtio_balloon *vb, int idx,
                   u16 tag, u64 val)
{
    BUG_ON(idx >= VIRTIO_BALLOON_S_NR);
    vb->stats[idx].tag = tag;
    vb->stats[idx].val = val;
}

#define pages_to_bytes(x) ((u64)(x) << PAGE_SHIFT)

static void update_balloon_stats(struct virtio_balloon *vb)
{
    unsigned long events[NR_VM_EVENT_ITEMS];
    struct sysinfo i;
    int idx = 0;

    all_vm_events(events);
    si_meminfo(&i);

    update_stat(vb, idx++, VIRTIO_BALLOON_S_SWAP_IN,
                pages_to_bytes(events[PSWPIN]));
    update_stat(vb, idx++, VIRTIO_BALLOON_S_SWAP_OUT,
                pages_to_bytes(events[PSWPOUT]));
    update_stat(vb, idx++, VIRTIO_BALLOON_S_MAJFLT, events[PGMAJFAULT]);
    update_stat(vb, idx++, VIRTIO_BALLOON_S_MINFLT, events[PGFAULT]);
    update_stat(vb, idx++, VIRTIO_BALLOON_S_MEMFREE,
                pages_to_bytes(i.freeram));
    update_stat(vb, idx++, VIRTIO_BALLOON_S_MEMTOT,
                pages_to_bytes(i.totalram));
}

/*
 * While most virtqueues communicate guest-initiated requests to the hypervisor,
 * the stats queue operates in reverse.  The driver initializes the virtqueue
 * with a single buffer.  From that point forward, all conversations consist of
 * a hypervisor request (a call to this function) which directs us to refill
 * the virtqueue with a fresh stats buffer.  Since stats collection can sleep,
 * we notify our kthread which does the actual work via stats_handle_request().
 */
static void stats_request(struct virtqueue *vq)
{
    struct virtio_balloon *vb = vq->vdev->priv;

    vb->need_stats_update = 1;
    wake_up(&vb->config_change);
}

static void stats_handle_request(struct virtio_balloon *vb)
{
    struct virtqueue *vq;
    struct scatterlist sg;
    unsigned int len;

    vb->need_stats_update = 0;
    update_balloon_stats(vb);

    vq = vb->stats_vq;
    if (!virtqueue_get_buf(vq, &len))
        return;
    sg_init_one(&sg, vb->stats, sizeof(vb->stats));
    if (virtqueue_add_buf(vq, &sg, 1, 0, vb, GFP_KERNEL) < 0)
        BUG();
    virtqueue_kick(vq);
}

static void virtballoon_changed(struct virtio_device *vdev)
{
    struct virtio_balloon *vb = vdev->priv;

    wake_up(&vb->config_change);
}

static inline s64 towards_target(struct virtio_balloon *vb)
{
    __le32 v;
    s64 target;

    vb->vdev->config->get(vb->vdev,
                  offsetof(struct virtio_balloon_config, num_pages),
                  &v, sizeof(v));
    target = le32_to_cpu(v);
    return target - vb->num_pages;
}

static void update_balloon_size(struct virtio_balloon *vb)
{
    __le32 actual = cpu_to_le32(vb->num_pages);

    vb->vdev->config->set(vb->vdev,
                  offsetof(struct virtio_balloon_config, actual),
                  &actual, sizeof(actual));
}

static int balloon(void *_vballoon)
{
    struct virtio_balloon *vb = _vballoon;

    set_freezable();
    while (!kthread_should_stop()) {
        s64 diff;

        try_to_freeze();
        wait_event_interruptible(vb->config_change,
                     (diff = towards_target(vb)) != 0
                     || vb->need_stats_update
                     || kthread_should_stop()
                     || freezing(current));
        if (vb->need_stats_update)
            stats_handle_request(vb);
        if (diff > 0)
            fill_balloon(vb, diff);
        else if (diff < 0)
            leak_balloon(vb, -diff);
        update_balloon_size(vb);
    }
    return 0;
}

static int init_vqs(struct virtio_balloon *vb)
{
    struct virtqueue *vqs[3];
    vq_callback_t *callbacks[] = { balloon_ack, balloon_ack, stats_request };
    const char *names[] = { "inflate", "deflate", "stats" };
    int err, nvqs;

    /*
     * We expect two virtqueues: inflate and deflate, and
     * optionally stat.
     */
    nvqs = virtio_has_feature(vb->vdev, VIRTIO_BALLOON_F_STATS_VQ) ? 3 : 2;
    err = vb->vdev->config->find_vqs(vb->vdev, nvqs, vqs, callbacks, names);
    if (err)
        return err;

    vb->inflate_vq = vqs[0];
    vb->deflate_vq = vqs[1];
    if (virtio_has_feature(vb->vdev, VIRTIO_BALLOON_F_STATS_VQ)) {
        struct scatterlist sg;
        vb->stats_vq = vqs[2];

        /*
         * Prime this virtqueue with one buffer so the hypervisor can
         * use it to signal us later.
         */
        sg_init_one(&sg, vb->stats, sizeof vb->stats);
        if (virtqueue_add_buf(vb->stats_vq, &sg, 1, 0, vb, GFP_KERNEL)
            < 0)
            BUG();
        virtqueue_kick(vb->stats_vq);
    }
    return 0;
}

static int virtballoon_probe(struct virtio_device *vdev)
{
    struct virtio_balloon *vb;
    int err;

    vdev->priv = vb = kmalloc(sizeof(*vb), GFP_KERNEL);
    if (!vb) {
        err = -ENOMEM;
        goto out;
    }

    INIT_LIST_HEAD(&vb->pages);
    vb->num_pages = 0;
    init_waitqueue_head(&vb->config_change);
    init_waitqueue_head(&vb->acked);
    vb->vdev = vdev;
    vb->need_stats_update = 0;

    err = init_vqs(vb);
    if (err)
        goto out_free_vb;

    vb->thread = kthread_run(balloon, vb, "vballoon");
    if (IS_ERR(vb->thread)) {
        err = PTR_ERR(vb->thread);
        goto out_del_vqs;
    }

    return 0;

out_del_vqs:
    vdev->config->del_vqs(vdev);
out_free_vb:
    kfree(vb);
out:
    return err;
}

static void remove_common(struct virtio_balloon *vb)
{
    /* There might be pages left in the balloon: free them. */
    while (vb->num_pages)
        leak_balloon(vb, vb->num_pages);
    update_balloon_size(vb);

    /* Now we reset the device so we can clean up the queues. */
    vb->vdev->config->reset(vb->vdev);

    vb->vdev->config->del_vqs(vb->vdev);
}

static void __devexit virtballoon_remove(struct virtio_device *vdev)
{
    struct virtio_balloon *vb = vdev->priv;

    kthread_stop(vb->thread);
    remove_common(vb);
    kfree(vb);
}

#ifdef CONFIG_PM
static int virtballoon_freeze(struct virtio_device *vdev)
{
    struct virtio_balloon *vb = vdev->priv;

    /*
     * The kthread is already frozen by the PM core before this
     * function is called.
     */

    remove_common(vb);
    return 0;
}

static int virtballoon_restore(struct virtio_device *vdev)
{
    struct virtio_balloon *vb = vdev->priv;
    int ret;

    ret = init_vqs(vdev->priv);
    if (ret)
        return ret;

    fill_balloon(vb, towards_target(vb));
    update_balloon_size(vb);
    return 0;
}
#endif

static unsigned int features[] = {
    VIRTIO_BALLOON_F_MUST_TELL_HOST,
    VIRTIO_BALLOON_F_STATS_VQ,
};

static struct virtio_driver virtio_balloon_driver = {
    .feature_table = features,
    .feature_table_size = ARRAY_SIZE(features),
    .driver.name =  KBUILD_MODNAME,
    .driver.owner = THIS_MODULE,
    .id_table = id_table,
    .probe =    virtballoon_probe,
    .remove =   __devexit_p(virtballoon_remove),
    .config_changed = virtballoon_changed,
#ifdef CONFIG_PM
    .freeze =   virtballoon_freeze,
    .restore =  virtballoon_restore,
#endif
};

static int __init init(void)
{
    return register_virtio_driver(&virtio_balloon_driver);
}

static void __exit fini(void)
{
    unregister_virtio_driver(&virtio_balloon_driver);
}
module_init(init);
module_exit(fini);

MODULE_DEVICE_TABLE(virtio, id_table);
MODULE_DESCRIPTION("Virtio balloon driver");
MODULE_LICENSE("GPL");