virtio_balloon: fix race by fill and leak

[mirror_ubuntu-zesty-kernel.git] / drivers / virtio / virtio_balloon.c

/*
 * 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>
#include <linux/balloon_compaction.h>
#include <linux/oom.h>
#include <linux/wait.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 (unsigned)(PAGE_SIZE >> VIRTIO_BALLOON_PFN_SHIFT)
#define VIRTIO_BALLOON_ARRAY_PFNS_MAX 256
#define OOM_VBALLOON_DEFAULT_PAGES 256
#define VIRTBALLOON_OOM_NOTIFY_PRIORITY 80

static int oom_pages = OOM_VBALLOON_DEFAULT_PAGES;
module_param(oom_pages, int, S_IRUSR | S_IWUSR);
MODULE_PARM_DESC(oom_pages, "pages to free on OOM");

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 are enqueued
         * at vb_dev_info->pages list.
         * Each page on this list adds VIRTIO_BALLOON_PAGES_PER_PAGE
         * to num_pages above.
         */
        struct balloon_dev_info vb_dev_info;

        /* Synchronize access/update to this struct virtio_balloon elements */
        struct mutex balloon_lock;

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

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

        /* To register callback in oom notifier call chain */
        struct notifier_block nb;
};

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. */
        virtqueue_add_outbuf(vq, &sg, 1, vb, GFP_KERNEL);
        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)
{
        struct balloon_dev_info *vb_dev_info = &vb->vb_dev_info;

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

        mutex_lock(&vb->balloon_lock);
        for (vb->num_pfns = 0; vb->num_pfns < num;
             vb->num_pfns += VIRTIO_BALLOON_PAGES_PER_PAGE) {
                struct page *page = balloon_page_enqueue(vb_dev_info);

                if (!page) {
                        dev_info_ratelimited(&vb->vdev->dev,
                                             "Out of puff! Can't get %u pages\n",
                                             VIRTIO_BALLOON_PAGES_PER_PAGE);
                        /* 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;
                if (!virtio_has_feature(vb->vdev,
                                        VIRTIO_BALLOON_F_DEFLATE_ON_OOM))
                        adjust_managed_page_count(page, -1);
        }

        /* Did we get any? */
        if (vb->num_pfns != 0)
                tell_host(vb, vb->inflate_vq);
        mutex_unlock(&vb->balloon_lock);
}

static void release_pages_balloon(struct virtio_balloon *vb)
{
        unsigned int i;

        /* Find pfns pointing at start of each page, get pages and free them. */
        for (i = 0; i < vb->num_pfns; i += VIRTIO_BALLOON_PAGES_PER_PAGE) {
                struct page *page = balloon_pfn_to_page(vb->pfns[i]);
                if (!virtio_has_feature(vb->vdev,
                                        VIRTIO_BALLOON_F_DEFLATE_ON_OOM))
                        adjust_managed_page_count(page, 1);
                put_page(page); /* balloon reference */
        }
}

static unsigned leak_balloon(struct virtio_balloon *vb, size_t num)
{
        unsigned num_freed_pages;
        struct page *page;
        struct balloon_dev_info *vb_dev_info = &vb->vb_dev_info;

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

        mutex_lock(&vb->balloon_lock);
        for (vb->num_pfns = 0; vb->num_pfns < num;
             vb->num_pfns += VIRTIO_BALLOON_PAGES_PER_PAGE) {
                page = balloon_page_dequeue(vb_dev_info);
                if (!page)
                        break;
                set_page_pfns(vb->pfns + vb->num_pfns, page);
                vb->num_pages -= VIRTIO_BALLOON_PAGES_PER_PAGE;
        }

        num_freed_pages = vb->num_pfns;
        /*
         * Note that if
         * virtio_has_feature(vdev, VIRTIO_BALLOON_F_MUST_TELL_HOST);
         * is true, we *have* to do it in this order
         */
        if (vb->num_pfns != 0)
                tell_host(vb, vb->deflate_vq);
        release_pages_balloon(vb);
        mutex_unlock(&vb->balloon_lock);
        return num_freed_pages;
}

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 = cpu_to_virtio16(vb->vdev, tag);
        vb->stats[idx].val = cpu_to_virtio64(vb->vdev, 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));
        virtqueue_add_outbuf(vq, &sg, 1, vb, GFP_KERNEL);
        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)
{
        s64 target;
        u32 num_pages;

        virtio_cread(vb->vdev, struct virtio_balloon_config, num_pages,
                     &num_pages);

        /* Legacy balloon config space is LE, unlike all other devices. */
        if (!virtio_has_feature(vb->vdev, VIRTIO_F_VERSION_1))
                num_pages = le32_to_cpu((__force __le32)num_pages);

        target = num_pages;
        return target - vb->num_pages;
}

static void update_balloon_size(struct virtio_balloon *vb)
{
        u32 actual = vb->num_pages;

        /* Legacy balloon config space is LE, unlike all other devices. */
        if (!virtio_has_feature(vb->vdev, VIRTIO_F_VERSION_1))
                actual = (__force u32)cpu_to_le32(actual);

        virtio_cwrite(vb->vdev, struct virtio_balloon_config, actual,
                      &actual);
}

/*
 * virtballoon_oom_notify - release pages when system is under severe
 *                          memory pressure (called from out_of_memory())
 * @self : notifier block struct
 * @dummy: not used
 * @parm : returned - number of freed pages
 *
 * The balancing of memory by use of the virtio balloon should not cause
 * the termination of processes while there are pages in the balloon.
 * If virtio balloon manages to release some memory, it will make the
 * system return and retry the allocation that forced the OOM killer
 * to run.
 */
static int virtballoon_oom_notify(struct notifier_block *self,
                                  unsigned long dummy, void *parm)
{
        struct virtio_balloon *vb;
        unsigned long *freed;
        unsigned num_freed_pages;

        vb = container_of(self, struct virtio_balloon, nb);
        if (!virtio_has_feature(vb->vdev, VIRTIO_BALLOON_F_DEFLATE_ON_OOM))
                return NOTIFY_OK;

        freed = parm;
        num_freed_pages = leak_balloon(vb, oom_pages);
        update_balloon_size(vb);
        *freed += num_freed_pages;

        return NOTIFY_OK;
}

static int balloon(void *_vballoon)
{
        struct virtio_balloon *vb = _vballoon;
        DEFINE_WAIT_FUNC(wait, woken_wake_function);

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

                try_to_freeze();

                add_wait_queue(&vb->config_change, &wait);
                for (;;) {
                        if ((diff = towards_target(vb)) != 0 ||
                            vb->need_stats_update ||
                            kthread_should_stop() ||
                            freezing(current))
                                break;
                        wait_woken(&wait, TASK_INTERRUPTIBLE, MAX_SCHEDULE_TIMEOUT);
                }
                remove_wait_queue(&vb->config_change, &wait);

                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);

                /*
                 * For large balloon changes, we could spend a lot of time
                 * and always have work to do.  Be nice if preempt disabled.
                 */
                cond_resched();
        }
        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 (it can't be broken yet!).
                 */
                sg_init_one(&sg, vb->stats, sizeof vb->stats);
                if (virtqueue_add_outbuf(vb->stats_vq, &sg, 1, vb, GFP_KERNEL)
                    < 0)
                        BUG();
                virtqueue_kick(vb->stats_vq);
        }
        return 0;
}

#ifdef CONFIG_BALLOON_COMPACTION
/*
 * virtballoon_migratepage - perform the balloon page migration on behalf of
 *                           a compation thread.     (called under page lock)
 * @vb_dev_info: the balloon device
 * @newpage: page that will replace the isolated page after migration finishes.
 * @page   : the isolated (old) page that is about to be migrated to newpage.
 * @mode   : compaction mode -- not used for balloon page migration.
 *
 * After a ballooned page gets isolated by compaction procedures, this is the
 * function that performs the page migration on behalf of a compaction thread
 * The page migration for virtio balloon is done in a simple swap fashion which
 * follows these two macro steps:
 *  1) insert newpage into vb->pages list and update the host about it;
 *  2) update the host about the old page removed from vb->pages list;
 *
 * This function preforms the balloon page migration task.
 * Called through balloon_mapping->a_ops->migratepage
 */
static int virtballoon_migratepage(struct balloon_dev_info *vb_dev_info,
                struct page *newpage, struct page *page, enum migrate_mode mode)
{
        struct virtio_balloon *vb = container_of(vb_dev_info,
                        struct virtio_balloon, vb_dev_info);
        unsigned long flags;

        /*
         * In order to avoid lock contention while migrating pages concurrently
         * to leak_balloon() or fill_balloon() we just give up the balloon_lock
         * this turn, as it is easier to retry the page migration later.
         * This also prevents fill_balloon() getting stuck into a mutex
         * recursion in the case it ends up triggering memory compaction
         * while it is attempting to inflate the ballon.
         */
        if (!mutex_trylock(&vb->balloon_lock))
                return -EAGAIN;

        get_page(newpage); /* balloon reference */

        /* balloon's page migration 1st step  -- inflate "newpage" */
        spin_lock_irqsave(&vb_dev_info->pages_lock, flags);
        balloon_page_insert(vb_dev_info, newpage);
        vb_dev_info->isolated_pages--;
        __count_vm_event(BALLOON_MIGRATE);
        spin_unlock_irqrestore(&vb_dev_info->pages_lock, flags);
        vb->num_pfns = VIRTIO_BALLOON_PAGES_PER_PAGE;
        set_page_pfns(vb->pfns, newpage);
        tell_host(vb, vb->inflate_vq);

        /* balloon's page migration 2nd step -- deflate "page" */
        balloon_page_delete(page);
        vb->num_pfns = VIRTIO_BALLOON_PAGES_PER_PAGE;
        set_page_pfns(vb->pfns, page);
        tell_host(vb, vb->deflate_vq);

        mutex_unlock(&vb->balloon_lock);

        put_page(page); /* balloon reference */

        return MIGRATEPAGE_SUCCESS;
}
#endif /* CONFIG_BALLOON_COMPACTION */

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

        if (!vdev->config->get) {
                dev_err(&vdev->dev, "%s failure: config access disabled\n",
                        __func__);
                return -EINVAL;
        }

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

        vb->num_pages = 0;
        mutex_init(&vb->balloon_lock);
        init_waitqueue_head(&vb->config_change);
        init_waitqueue_head(&vb->acked);
        vb->vdev = vdev;
        vb->need_stats_update = 0;

        balloon_devinfo_init(&vb->vb_dev_info);
#ifdef CONFIG_BALLOON_COMPACTION
        vb->vb_dev_info.migratepage = virtballoon_migratepage;
#endif

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

        vb->nb.notifier_call = virtballoon_oom_notify;
        vb->nb.priority = VIRTBALLOON_OOM_NOTIFY_PRIORITY;
        err = register_oom_notifier(&vb->nb);
        if (err < 0)
                goto out_oom_notify;

        virtio_device_ready(vdev);

        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:
        unregister_oom_notifier(&vb->nb);
out_oom_notify:
        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 virtballoon_remove(struct virtio_device *vdev)
{
        struct virtio_balloon *vb = vdev->priv;

        unregister_oom_notifier(&vb->nb);
        kthread_stop(vb->thread);
        remove_common(vb);
        kfree(vb);
}

#ifdef CONFIG_PM_SLEEP
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;

        virtio_device_ready(vdev);

        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,
        VIRTIO_BALLOON_F_DEFLATE_ON_OOM,
};

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 =       virtballoon_remove,
        .config_changed = virtballoon_changed,
#ifdef CONFIG_PM_SLEEP
        .freeze =       virtballoon_freeze,
        .restore =      virtballoon_restore,
#endif
};

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