Adding upstream version 5.10.209.upstream/5.10.209upstream

Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>

1 files changed, 1160 insertions, 0 deletions

diff --git a/drivers/virtio/virtio_balloon.c b/drivers/virtio/virtio_balloon.c
new file mode 100644
index 000000000..935ea2f3d
--- /dev/null
+++ b/drivers/virtio/virtio_balloon.c
@@ -0,0 +1,1160 @@
+// SPDX-License-Identifier: GPL-2.0-or-later
+/*
+ * Virtio balloon implementation, inspired by Dor Laor and Marcelo
+ * Tosatti's implementations.
+ *
+ *  Copyright 2008 Rusty Russell IBM Corporation
+ */
+
+#include <linux/virtio.h>
+#include <linux/virtio_balloon.h>
+#include <linux/swap.h>
+#include <linux/workqueue.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>
+#include <linux/mm.h>
+#include <linux/mount.h>
+#include <linux/magic.h>
+#include <linux/pseudo_fs.h>
+#include <linux/page_reporting.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
+/* Maximum number of (4k) pages to deflate on OOM notifications. */
+#define VIRTIO_BALLOON_OOM_NR_PAGES 256
+#define VIRTIO_BALLOON_OOM_NOTIFY_PRIORITY 80
+
+#define VIRTIO_BALLOON_FREE_PAGE_ALLOC_FLAG (__GFP_NORETRY | __GFP_NOWARN | \
+					     __GFP_NOMEMALLOC)
+/* The order of free page blocks to report to host */
+#define VIRTIO_BALLOON_HINT_BLOCK_ORDER (MAX_ORDER - 1)
+/* The size of a free page block in bytes */
+#define VIRTIO_BALLOON_HINT_BLOCK_BYTES \
+	(1 << (VIRTIO_BALLOON_HINT_BLOCK_ORDER + PAGE_SHIFT))
+#define VIRTIO_BALLOON_HINT_BLOCK_PAGES (1 << VIRTIO_BALLOON_HINT_BLOCK_ORDER)
+
+#ifdef CONFIG_BALLOON_COMPACTION
+static struct vfsmount *balloon_mnt;
+#endif
+
+enum virtio_balloon_vq {
+	VIRTIO_BALLOON_VQ_INFLATE,
+	VIRTIO_BALLOON_VQ_DEFLATE,
+	VIRTIO_BALLOON_VQ_STATS,
+	VIRTIO_BALLOON_VQ_FREE_PAGE,
+	VIRTIO_BALLOON_VQ_REPORTING,
+	VIRTIO_BALLOON_VQ_MAX
+};
+
+enum virtio_balloon_config_read {
+	VIRTIO_BALLOON_CONFIG_READ_CMD_ID = 0,
+};
+
+struct virtio_balloon {
+	struct virtio_device *vdev;
+	struct virtqueue *inflate_vq, *deflate_vq, *stats_vq, *free_page_vq;
+
+	/* Balloon's own wq for cpu-intensive work items */
+	struct workqueue_struct *balloon_wq;
+	/* The free page reporting work item submitted to the balloon wq */
+	struct work_struct report_free_page_work;
+
+	/* The balloon servicing is delegated to a freezable workqueue. */
+	struct work_struct update_balloon_stats_work;
+	struct work_struct update_balloon_size_work;
+
+	/* Prevent updating balloon when it is being canceled. */
+	spinlock_t stop_update_lock;
+	bool stop_update;
+	/* Bitmap to indicate if reading the related config fields are needed */
+	unsigned long config_read_bitmap;
+
+	/* The list of allocated free pages, waiting to be given back to mm */
+	struct list_head free_page_list;
+	spinlock_t free_page_list_lock;
+	/* The number of free page blocks on the above list */
+	unsigned long num_free_page_blocks;
+	/*
+	 * The cmd id received from host.
+	 * Read it via virtio_balloon_cmd_id_received to get the latest value
+	 * sent from host.
+	 */
+	u32 cmd_id_received_cache;
+	/* The cmd id that is actively in use */
+	__virtio32 cmd_id_active;
+	/* Buffer to store the stop sign */
+	__virtio32 cmd_id_stop;
+
+	/* 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;
+	__virtio32 pfns[VIRTIO_BALLOON_ARRAY_PFNS_MAX];
+
+	/* Memory statistics */
+	struct virtio_balloon_stat stats[VIRTIO_BALLOON_S_NR];
+
+	/* Shrinker to return free pages - VIRTIO_BALLOON_F_FREE_PAGE_HINT */
+	struct shrinker shrinker;
+
+	/* OOM notifier to deflate on OOM - VIRTIO_BALLOON_F_DEFLATE_ON_OOM */
+	struct notifier_block oom_nb;
+
+	/* Free page reporting device */
+	struct virtqueue *reporting_vq;
+	struct page_reporting_dev_info pr_dev_info;
+};
+
+static const 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 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 int virtballoon_free_page_report(struct page_reporting_dev_info *pr_dev_info,
+				   struct scatterlist *sg, unsigned int nents)
+{
+	struct virtio_balloon *vb =
+		container_of(pr_dev_info, struct virtio_balloon, pr_dev_info);
+	struct virtqueue *vq = vb->reporting_vq;
+	unsigned int unused, err;
+
+	/* We should always be able to add these buffers to an empty queue. */
+	err = virtqueue_add_inbuf(vq, sg, nents, vb, GFP_NOWAIT | __GFP_NOWARN);
+
+	/*
+	 * In the extremely unlikely case that something has occurred and we
+	 * are able to trigger an error we will simply display a warning
+	 * and exit without actually processing the pages.
+	 */
+	if (WARN_ON_ONCE(err))
+		return err;
+
+	virtqueue_kick(vq);
+
+	/* When host has read buffer, this completes via balloon_ack */
+	wait_event(vb->acked, virtqueue_get_buf(vq, &unused));
+
+	return 0;
+}
+
+static void set_page_pfns(struct virtio_balloon *vb,
+			  __virtio32 pfns[], struct page *page)
+{
+	unsigned int i;
+
+	BUILD_BUG_ON(VIRTIO_BALLOON_PAGES_PER_PAGE > VIRTIO_BALLOON_ARRAY_PFNS_MAX);
+
+	/*
+	 * 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] = cpu_to_virtio32(vb->vdev,
+					  page_to_balloon_pfn(page) + i);
+}
+
+static unsigned fill_balloon(struct virtio_balloon *vb, size_t num)
+{
+	unsigned num_allocated_pages;
+	unsigned num_pfns;
+	struct page *page;
+	LIST_HEAD(pages);
+
+	/* We can only do one array worth at a time. */
+	num = min(num, ARRAY_SIZE(vb->pfns));
+
+	for (num_pfns = 0; num_pfns < num;
+	     num_pfns += VIRTIO_BALLOON_PAGES_PER_PAGE) {
+		struct page *page = balloon_page_alloc();
+
+		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;
+		}
+
+		balloon_page_push(&pages, page);
+	}
+
+	mutex_lock(&vb->balloon_lock);
+
+	vb->num_pfns = 0;
+
+	while ((page = balloon_page_pop(&pages))) {
+		balloon_page_enqueue(&vb->vb_dev_info, page);
+
+		set_page_pfns(vb, 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);
+		vb->num_pfns += VIRTIO_BALLOON_PAGES_PER_PAGE;
+	}
+
+	num_allocated_pages = vb->num_pfns;
+	/* Did we get any? */
+	if (vb->num_pfns != 0)
+		tell_host(vb, vb->inflate_vq);
+	mutex_unlock(&vb->balloon_lock);
+
+	return num_allocated_pages;
+}
+
+static void release_pages_balloon(struct virtio_balloon *vb,
+				 struct list_head *pages)
+{
+	struct page *page, *next;
+
+	list_for_each_entry_safe(page, next, pages, lru) {
+		if (!virtio_has_feature(vb->vdev,
+					VIRTIO_BALLOON_F_DEFLATE_ON_OOM))
+			adjust_managed_page_count(page, 1);
+		list_del(&page->lru);
+		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;
+	LIST_HEAD(pages);
+
+	/* We can only do one array worth at a time. */
+	num = min(num, ARRAY_SIZE(vb->pfns));
+
+	mutex_lock(&vb->balloon_lock);
+	/* We can't release more pages than taken */
+	num = min(num, (size_t)vb->num_pages);
+	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, vb->pfns + vb->num_pfns, page);
+		list_add(&page->lru, &pages);
+		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, &pages);
+	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 unsigned int update_balloon_stats(struct virtio_balloon *vb)
+{
+	unsigned long events[NR_VM_EVENT_ITEMS];
+	struct sysinfo i;
+	unsigned int idx = 0;
+	long available;
+	unsigned long caches;
+
+	all_vm_events(events);
+	si_meminfo(&i);
+
+	available = si_mem_available();
+	caches = global_node_page_state(NR_FILE_PAGES);
+
+#ifdef CONFIG_VM_EVENT_COUNTERS
+	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]);
+#ifdef CONFIG_HUGETLB_PAGE
+	update_stat(vb, idx++, VIRTIO_BALLOON_S_HTLB_PGALLOC,
+		    events[HTLB_BUDDY_PGALLOC]);
+	update_stat(vb, idx++, VIRTIO_BALLOON_S_HTLB_PGFAIL,
+		    events[HTLB_BUDDY_PGALLOC_FAIL]);
+#endif
+#endif
+	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));
+	update_stat(vb, idx++, VIRTIO_BALLOON_S_AVAIL,
+				pages_to_bytes(available));
+	update_stat(vb, idx++, VIRTIO_BALLOON_S_CACHES,
+				pages_to_bytes(caches));
+
+	return idx;
+}
+
+/*
+ * 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 delegate the job to a freezable workqueue that will do the actual work via
+ * stats_handle_request().
+ */
+static void stats_request(struct virtqueue *vq)
+{
+	struct virtio_balloon *vb = vq->vdev->priv;
+
+	spin_lock(&vb->stop_update_lock);
+	if (!vb->stop_update)
+		queue_work(system_freezable_wq, &vb->update_balloon_stats_work);
+	spin_unlock(&vb->stop_update_lock);
+}
+
+static void stats_handle_request(struct virtio_balloon *vb)
+{
+	struct virtqueue *vq;
+	struct scatterlist sg;
+	unsigned int len, num_stats;
+
+	num_stats = update_balloon_stats(vb);
+
+	vq = vb->stats_vq;
+	if (!virtqueue_get_buf(vq, &len))
+		return;
+	sg_init_one(&sg, vb->stats, sizeof(vb->stats[0]) * num_stats);
+	virtqueue_add_outbuf(vq, &sg, 1, vb, GFP_KERNEL);
+	virtqueue_kick(vq);
+}
+
+static inline s64 towards_target(struct virtio_balloon *vb)
+{
+	s64 target;
+	u32 num_pages;
+
+	/* Legacy balloon config space is LE, unlike all other devices. */
+	virtio_cread_le(vb->vdev, struct virtio_balloon_config, num_pages,
+			&num_pages);
+
+	/*
+	 * Aligned up to guest page size to avoid inflating and deflating
+	 * balloon endlessly.
+	 */
+	target = ALIGN(num_pages, VIRTIO_BALLOON_PAGES_PER_PAGE);
+	return target - vb->num_pages;
+}
+
+/* Gives back @num_to_return blocks of free pages to mm. */
+static unsigned long return_free_pages_to_mm(struct virtio_balloon *vb,
+					     unsigned long num_to_return)
+{
+	struct page *page;
+	unsigned long num_returned;
+
+	spin_lock_irq(&vb->free_page_list_lock);
+	for (num_returned = 0; num_returned < num_to_return; num_returned++) {
+		page = balloon_page_pop(&vb->free_page_list);
+		if (!page)
+			break;
+		free_pages((unsigned long)page_address(page),
+			   VIRTIO_BALLOON_HINT_BLOCK_ORDER);
+	}
+	vb->num_free_page_blocks -= num_returned;
+	spin_unlock_irq(&vb->free_page_list_lock);
+
+	return num_returned;
+}
+
+static void virtio_balloon_queue_free_page_work(struct virtio_balloon *vb)
+{
+	if (!virtio_has_feature(vb->vdev, VIRTIO_BALLOON_F_FREE_PAGE_HINT))
+		return;
+
+	/* No need to queue the work if the bit was already set. */
+	if (test_and_set_bit(VIRTIO_BALLOON_CONFIG_READ_CMD_ID,
+			     &vb->config_read_bitmap))
+		return;
+
+	queue_work(vb->balloon_wq, &vb->report_free_page_work);
+}
+
+static void virtballoon_changed(struct virtio_device *vdev)
+{
+	struct virtio_balloon *vb = vdev->priv;
+	unsigned long flags;
+
+	spin_lock_irqsave(&vb->stop_update_lock, flags);
+	if (!vb->stop_update) {
+		queue_work(system_freezable_wq,
+			   &vb->update_balloon_size_work);
+		virtio_balloon_queue_free_page_work(vb);
+	}
+	spin_unlock_irqrestore(&vb->stop_update_lock, flags);
+}
+
+static void update_balloon_size(struct virtio_balloon *vb)
+{
+	u32 actual = vb->num_pages;
+
+	/* Legacy balloon config space is LE, unlike all other devices. */
+	virtio_cwrite_le(vb->vdev, struct virtio_balloon_config, actual,
+			 &actual);
+}
+
+static void update_balloon_stats_func(struct work_struct *work)
+{
+	struct virtio_balloon *vb;
+
+	vb = container_of(work, struct virtio_balloon,
+			  update_balloon_stats_work);
+	stats_handle_request(vb);
+}
+
+static void update_balloon_size_func(struct work_struct *work)
+{
+	struct virtio_balloon *vb;
+	s64 diff;
+
+	vb = container_of(work, struct virtio_balloon,
+			  update_balloon_size_work);
+	diff = towards_target(vb);
+
+	if (!diff)
+		return;
+
+	if (diff > 0)
+		diff -= fill_balloon(vb, diff);
+	else
+		diff += leak_balloon(vb, -diff);
+	update_balloon_size(vb);
+
+	if (diff)
+		queue_work(system_freezable_wq, work);
+}
+
+static int init_vqs(struct virtio_balloon *vb)
+{
+	struct virtqueue *vqs[VIRTIO_BALLOON_VQ_MAX];
+	vq_callback_t *callbacks[VIRTIO_BALLOON_VQ_MAX];
+	const char *names[VIRTIO_BALLOON_VQ_MAX];
+	int err;
+
+	/*
+	 * Inflateq and deflateq are used unconditionally. The names[]
+	 * will be NULL if the related feature is not enabled, which will
+	 * cause no allocation for the corresponding virtqueue in find_vqs.
+	 */
+	callbacks[VIRTIO_BALLOON_VQ_INFLATE] = balloon_ack;
+	names[VIRTIO_BALLOON_VQ_INFLATE] = "inflate";
+	callbacks[VIRTIO_BALLOON_VQ_DEFLATE] = balloon_ack;
+	names[VIRTIO_BALLOON_VQ_DEFLATE] = "deflate";
+	callbacks[VIRTIO_BALLOON_VQ_STATS] = NULL;
+	names[VIRTIO_BALLOON_VQ_STATS] = NULL;
+	callbacks[VIRTIO_BALLOON_VQ_FREE_PAGE] = NULL;
+	names[VIRTIO_BALLOON_VQ_FREE_PAGE] = NULL;
+	names[VIRTIO_BALLOON_VQ_REPORTING] = NULL;
+
+	if (virtio_has_feature(vb->vdev, VIRTIO_BALLOON_F_STATS_VQ)) {
+		names[VIRTIO_BALLOON_VQ_STATS] = "stats";
+		callbacks[VIRTIO_BALLOON_VQ_STATS] = stats_request;
+	}
+
+	if (virtio_has_feature(vb->vdev, VIRTIO_BALLOON_F_FREE_PAGE_HINT)) {
+		names[VIRTIO_BALLOON_VQ_FREE_PAGE] = "free_page_vq";
+		callbacks[VIRTIO_BALLOON_VQ_FREE_PAGE] = NULL;
+	}
+
+	if (virtio_has_feature(vb->vdev, VIRTIO_BALLOON_F_REPORTING)) {
+		names[VIRTIO_BALLOON_VQ_REPORTING] = "reporting_vq";
+		callbacks[VIRTIO_BALLOON_VQ_REPORTING] = balloon_ack;
+	}
+
+	err = vb->vdev->config->find_vqs(vb->vdev, VIRTIO_BALLOON_VQ_MAX,
+					 vqs, callbacks, names, NULL, NULL);
+	if (err)
+		return err;
+
+	vb->inflate_vq = vqs[VIRTIO_BALLOON_VQ_INFLATE];
+	vb->deflate_vq = vqs[VIRTIO_BALLOON_VQ_DEFLATE];
+	if (virtio_has_feature(vb->vdev, VIRTIO_BALLOON_F_STATS_VQ)) {
+		struct scatterlist sg;
+		unsigned int num_stats;
+		vb->stats_vq = vqs[VIRTIO_BALLOON_VQ_STATS];
+
+		/*
+		 * Prime this virtqueue with one buffer so the hypervisor can
+		 * use it to signal us later (it can't be broken yet!).
+		 */
+		num_stats = update_balloon_stats(vb);
+
+		sg_init_one(&sg, vb->stats, sizeof(vb->stats[0]) * num_stats);
+		err = virtqueue_add_outbuf(vb->stats_vq, &sg, 1, vb,
+					   GFP_KERNEL);
+		if (err) {
+			dev_warn(&vb->vdev->dev, "%s: add stat_vq failed\n",
+				 __func__);
+			return err;
+		}
+		virtqueue_kick(vb->stats_vq);
+	}
+
+	if (virtio_has_feature(vb->vdev, VIRTIO_BALLOON_F_FREE_PAGE_HINT))
+		vb->free_page_vq = vqs[VIRTIO_BALLOON_VQ_FREE_PAGE];
+
+	if (virtio_has_feature(vb->vdev, VIRTIO_BALLOON_F_REPORTING))
+		vb->reporting_vq = vqs[VIRTIO_BALLOON_VQ_REPORTING];
+
+	return 0;
+}
+
+static u32 virtio_balloon_cmd_id_received(struct virtio_balloon *vb)
+{
+	if (test_and_clear_bit(VIRTIO_BALLOON_CONFIG_READ_CMD_ID,
+			       &vb->config_read_bitmap)) {
+		/* Legacy balloon config space is LE, unlike all other devices. */
+		virtio_cread_le(vb->vdev, struct virtio_balloon_config,
+				free_page_hint_cmd_id,
+				&vb->cmd_id_received_cache);
+	}
+
+	return vb->cmd_id_received_cache;
+}
+
+static int send_cmd_id_start(struct virtio_balloon *vb)
+{
+	struct scatterlist sg;
+	struct virtqueue *vq = vb->free_page_vq;
+	int err, unused;
+
+	/* Detach all the used buffers from the vq */
+	while (virtqueue_get_buf(vq, &unused))
+		;
+
+	vb->cmd_id_active = cpu_to_virtio32(vb->vdev,
+					virtio_balloon_cmd_id_received(vb));
+	sg_init_one(&sg, &vb->cmd_id_active, sizeof(vb->cmd_id_active));
+	err = virtqueue_add_outbuf(vq, &sg, 1, &vb->cmd_id_active, GFP_KERNEL);
+	if (!err)
+		virtqueue_kick(vq);
+	return err;
+}
+
+static int send_cmd_id_stop(struct virtio_balloon *vb)
+{
+	struct scatterlist sg;
+	struct virtqueue *vq = vb->free_page_vq;
+	int err, unused;
+
+	/* Detach all the used buffers from the vq */
+	while (virtqueue_get_buf(vq, &unused))
+		;
+
+	sg_init_one(&sg, &vb->cmd_id_stop, sizeof(vb->cmd_id_stop));
+	err = virtqueue_add_outbuf(vq, &sg, 1, &vb->cmd_id_stop, GFP_KERNEL);
+	if (!err)
+		virtqueue_kick(vq);
+	return err;
+}
+
+static int get_free_page_and_send(struct virtio_balloon *vb)
+{
+	struct virtqueue *vq = vb->free_page_vq;
+	struct page *page;
+	struct scatterlist sg;
+	int err, unused;
+	void *p;
+
+	/* Detach all the used buffers from the vq */
+	while (virtqueue_get_buf(vq, &unused))
+		;
+
+	page = alloc_pages(VIRTIO_BALLOON_FREE_PAGE_ALLOC_FLAG,
+			   VIRTIO_BALLOON_HINT_BLOCK_ORDER);
+	/*
+	 * When the allocation returns NULL, it indicates that we have got all
+	 * the possible free pages, so return -EINTR to stop.
+	 */
+	if (!page)
+		return -EINTR;
+
+	p = page_address(page);
+	sg_init_one(&sg, p, VIRTIO_BALLOON_HINT_BLOCK_BYTES);
+	/* There is always 1 entry reserved for the cmd id to use. */
+	if (vq->num_free > 1) {
+		err = virtqueue_add_inbuf(vq, &sg, 1, p, GFP_KERNEL);
+		if (unlikely(err)) {
+			free_pages((unsigned long)p,
+				   VIRTIO_BALLOON_HINT_BLOCK_ORDER);
+			return err;
+		}
+		virtqueue_kick(vq);
+		spin_lock_irq(&vb->free_page_list_lock);
+		balloon_page_push(&vb->free_page_list, page);
+		vb->num_free_page_blocks++;
+		spin_unlock_irq(&vb->free_page_list_lock);
+	} else {
+		/*
+		 * The vq has no available entry to add this page block, so
+		 * just free it.
+		 */
+		free_pages((unsigned long)p, VIRTIO_BALLOON_HINT_BLOCK_ORDER);
+	}
+
+	return 0;
+}
+
+static int send_free_pages(struct virtio_balloon *vb)
+{
+	int err;
+	u32 cmd_id_active;
+
+	while (1) {
+		/*
+		 * If a stop id or a new cmd id was just received from host,
+		 * stop the reporting.
+		 */
+		cmd_id_active = virtio32_to_cpu(vb->vdev, vb->cmd_id_active);
+		if (unlikely(cmd_id_active !=
+			     virtio_balloon_cmd_id_received(vb)))
+			break;
+
+		/*
+		 * The free page blocks are allocated and sent to host one by
+		 * one.
+		 */
+		err = get_free_page_and_send(vb);
+		if (err == -EINTR)
+			break;
+		else if (unlikely(err))
+			return err;
+	}
+
+	return 0;
+}
+
+static void virtio_balloon_report_free_page(struct virtio_balloon *vb)
+{
+	int err;
+	struct device *dev = &vb->vdev->dev;
+
+	/* Start by sending the received cmd id to host with an outbuf. */
+	err = send_cmd_id_start(vb);
+	if (unlikely(err))
+		dev_err(dev, "Failed to send a start id, err = %d\n", err);
+
+	err = send_free_pages(vb);
+	if (unlikely(err))
+		dev_err(dev, "Failed to send a free page, err = %d\n", err);
+
+	/* End by sending a stop id to host with an outbuf. */
+	err = send_cmd_id_stop(vb);
+	if (unlikely(err))
+		dev_err(dev, "Failed to send a stop id, err = %d\n", err);
+}
+
+static void report_free_page_func(struct work_struct *work)
+{
+	struct virtio_balloon *vb = container_of(work, struct virtio_balloon,
+						 report_free_page_work);
+	u32 cmd_id_received;
+
+	cmd_id_received = virtio_balloon_cmd_id_received(vb);
+	if (cmd_id_received == VIRTIO_BALLOON_CMD_ID_DONE) {
+		/* Pass ULONG_MAX to give back all the free pages */
+		return_free_pages_to_mm(vb, ULONG_MAX);
+	} else if (cmd_id_received != VIRTIO_BALLOON_CMD_ID_STOP &&
+		   cmd_id_received !=
+		   virtio32_to_cpu(vb->vdev, vb->cmd_id_active)) {
+		virtio_balloon_report_free_page(vb);
+	}
+}
+
+#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 */
+
+	/*
+	  * When we migrate a page to a different zone and adjusted the
+	  * managed page count when inflating, we have to fixup the count of
+	  * both involved zones.
+	  */
+	if (!virtio_has_feature(vb->vdev, VIRTIO_BALLOON_F_DEFLATE_ON_OOM) &&
+	    page_zone(page) != page_zone(newpage)) {
+		adjust_managed_page_count(page, 1);
+		adjust_managed_page_count(newpage, -1);
+	}
+
+	/* 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, vb->pfns, newpage);
+	tell_host(vb, vb->inflate_vq);
+
+	/* balloon's page migration 2nd step -- deflate "page" */
+	spin_lock_irqsave(&vb_dev_info->pages_lock, flags);
+	balloon_page_delete(page);
+	spin_unlock_irqrestore(&vb_dev_info->pages_lock, flags);
+	vb->num_pfns = VIRTIO_BALLOON_PAGES_PER_PAGE;
+	set_page_pfns(vb, vb->pfns, page);
+	tell_host(vb, vb->deflate_vq);
+
+	mutex_unlock(&vb->balloon_lock);
+
+	put_page(page); /* balloon reference */
+
+	return MIGRATEPAGE_SUCCESS;
+}
+
+static int balloon_init_fs_context(struct fs_context *fc)
+{
+	return init_pseudo(fc, BALLOON_KVM_MAGIC) ? 0 : -ENOMEM;
+}
+
+static struct file_system_type balloon_fs = {
+	.name           = "balloon-kvm",
+	.init_fs_context = balloon_init_fs_context,
+	.kill_sb        = kill_anon_super,
+};
+
+#endif /* CONFIG_BALLOON_COMPACTION */
+
+static unsigned long shrink_free_pages(struct virtio_balloon *vb,
+				       unsigned long pages_to_free)
+{
+	unsigned long blocks_to_free, blocks_freed;
+
+	pages_to_free = round_up(pages_to_free,
+				 VIRTIO_BALLOON_HINT_BLOCK_PAGES);
+	blocks_to_free = pages_to_free / VIRTIO_BALLOON_HINT_BLOCK_PAGES;
+	blocks_freed = return_free_pages_to_mm(vb, blocks_to_free);
+
+	return blocks_freed * VIRTIO_BALLOON_HINT_BLOCK_PAGES;
+}
+
+static unsigned long virtio_balloon_shrinker_scan(struct shrinker *shrinker,
+						  struct shrink_control *sc)
+{
+	struct virtio_balloon *vb = container_of(shrinker,
+					struct virtio_balloon, shrinker);
+
+	return shrink_free_pages(vb, sc->nr_to_scan);
+}
+
+static unsigned long virtio_balloon_shrinker_count(struct shrinker *shrinker,
+						   struct shrink_control *sc)
+{
+	struct virtio_balloon *vb = container_of(shrinker,
+					struct virtio_balloon, shrinker);
+
+	return vb->num_free_page_blocks * VIRTIO_BALLOON_HINT_BLOCK_PAGES;
+}
+
+static int virtio_balloon_oom_notify(struct notifier_block *nb,
+				     unsigned long dummy, void *parm)
+{
+	struct virtio_balloon *vb = container_of(nb,
+						 struct virtio_balloon, oom_nb);
+	unsigned long *freed = parm;
+
+	*freed += leak_balloon(vb, VIRTIO_BALLOON_OOM_NR_PAGES) /
+		  VIRTIO_BALLOON_PAGES_PER_PAGE;
+	update_balloon_size(vb);
+
+	return NOTIFY_OK;
+}
+
+static void virtio_balloon_unregister_shrinker(struct virtio_balloon *vb)
+{
+	unregister_shrinker(&vb->shrinker);
+}
+
+static int virtio_balloon_register_shrinker(struct virtio_balloon *vb)
+{
+	vb->shrinker.scan_objects = virtio_balloon_shrinker_scan;
+	vb->shrinker.count_objects = virtio_balloon_shrinker_count;
+	vb->shrinker.seeks = DEFAULT_SEEKS;
+
+	return register_shrinker(&vb->shrinker);
+}
+
+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 = kzalloc(sizeof(*vb), GFP_KERNEL);
+	if (!vb) {
+		err = -ENOMEM;
+		goto out;
+	}
+
+	INIT_WORK(&vb->update_balloon_stats_work, update_balloon_stats_func);
+	INIT_WORK(&vb->update_balloon_size_work, update_balloon_size_func);
+	spin_lock_init(&vb->stop_update_lock);
+	mutex_init(&vb->balloon_lock);
+	init_waitqueue_head(&vb->acked);
+	vb->vdev = vdev;
+
+	balloon_devinfo_init(&vb->vb_dev_info);
+
+	err = init_vqs(vb);
+	if (err)
+		goto out_free_vb;
+
+#ifdef CONFIG_BALLOON_COMPACTION
+	balloon_mnt = kern_mount(&balloon_fs);
+	if (IS_ERR(balloon_mnt)) {
+		err = PTR_ERR(balloon_mnt);
+		goto out_del_vqs;
+	}
+
+	vb->vb_dev_info.migratepage = virtballoon_migratepage;
+	vb->vb_dev_info.inode = alloc_anon_inode(balloon_mnt->mnt_sb);
+	if (IS_ERR(vb->vb_dev_info.inode)) {
+		err = PTR_ERR(vb->vb_dev_info.inode);
+		goto out_kern_unmount;
+	}
+	vb->vb_dev_info.inode->i_mapping->a_ops = &balloon_aops;
+#endif
+	if (virtio_has_feature(vdev, VIRTIO_BALLOON_F_FREE_PAGE_HINT)) {
+		/*
+		 * There is always one entry reserved for cmd id, so the ring
+		 * size needs to be at least two to report free page hints.
+		 */
+		if (virtqueue_get_vring_size(vb->free_page_vq) < 2) {
+			err = -ENOSPC;
+			goto out_iput;
+		}
+		vb->balloon_wq = alloc_workqueue("balloon-wq",
+					WQ_FREEZABLE | WQ_CPU_INTENSIVE, 0);
+		if (!vb->balloon_wq) {
+			err = -ENOMEM;
+			goto out_iput;
+		}
+		INIT_WORK(&vb->report_free_page_work, report_free_page_func);
+		vb->cmd_id_received_cache = VIRTIO_BALLOON_CMD_ID_STOP;
+		vb->cmd_id_active = cpu_to_virtio32(vb->vdev,
+						  VIRTIO_BALLOON_CMD_ID_STOP);
+		vb->cmd_id_stop = cpu_to_virtio32(vb->vdev,
+						  VIRTIO_BALLOON_CMD_ID_STOP);
+		spin_lock_init(&vb->free_page_list_lock);
+		INIT_LIST_HEAD(&vb->free_page_list);
+		/*
+		 * We're allowed to reuse any free pages, even if they are
+		 * still to be processed by the host.
+		 */
+		err = virtio_balloon_register_shrinker(vb);
+		if (err)
+			goto out_del_balloon_wq;
+	}
+
+	if (virtio_has_feature(vb->vdev, VIRTIO_BALLOON_F_DEFLATE_ON_OOM)) {
+		vb->oom_nb.notifier_call = virtio_balloon_oom_notify;
+		vb->oom_nb.priority = VIRTIO_BALLOON_OOM_NOTIFY_PRIORITY;
+		err = register_oom_notifier(&vb->oom_nb);
+		if (err < 0)
+			goto out_unregister_shrinker;
+	}
+
+	if (virtio_has_feature(vdev, VIRTIO_BALLOON_F_PAGE_POISON)) {
+		/* Start with poison val of 0 representing general init */
+		__u32 poison_val = 0;
+
+		/*
+		 * Let the hypervisor know that we are expecting a
+		 * specific value to be written back in balloon pages.
+		 *
+		 * If the PAGE_POISON value was larger than a byte we would
+		 * need to byte swap poison_val here to guarantee it is
+		 * little-endian. However for now it is a single byte so we
+		 * can pass it as-is.
+		 */
+		if (!want_init_on_free())
+			memset(&poison_val, PAGE_POISON, sizeof(poison_val));
+
+		virtio_cwrite_le(vb->vdev, struct virtio_balloon_config,
+				 poison_val, &poison_val);
+	}
+
+	vb->pr_dev_info.report = virtballoon_free_page_report;
+	if (virtio_has_feature(vb->vdev, VIRTIO_BALLOON_F_REPORTING)) {
+		unsigned int capacity;
+
+		capacity = virtqueue_get_vring_size(vb->reporting_vq);
+		if (capacity < PAGE_REPORTING_CAPACITY) {
+			err = -ENOSPC;
+			goto out_unregister_oom;
+		}
+
+		err = page_reporting_register(&vb->pr_dev_info);
+		if (err)
+			goto out_unregister_oom;
+	}
+
+	virtio_device_ready(vdev);
+
+	if (towards_target(vb))
+		virtballoon_changed(vdev);
+	return 0;
+
+out_unregister_oom:
+	if (virtio_has_feature(vb->vdev, VIRTIO_BALLOON_F_DEFLATE_ON_OOM))
+		unregister_oom_notifier(&vb->oom_nb);
+out_unregister_shrinker:
+	if (virtio_has_feature(vb->vdev, VIRTIO_BALLOON_F_FREE_PAGE_HINT))
+		virtio_balloon_unregister_shrinker(vb);
+out_del_balloon_wq:
+	if (virtio_has_feature(vdev, VIRTIO_BALLOON_F_FREE_PAGE_HINT))
+		destroy_workqueue(vb->balloon_wq);
+out_iput:
+#ifdef CONFIG_BALLOON_COMPACTION
+	iput(vb->vb_dev_info.inode);
+out_kern_unmount:
+	kern_unmount(balloon_mnt);
+out_del_vqs:
+#endif
+	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);
+
+	/* There might be free pages that are being reported: release them. */
+	if (virtio_has_feature(vb->vdev, VIRTIO_BALLOON_F_FREE_PAGE_HINT))
+		return_free_pages_to_mm(vb, ULONG_MAX);
+
+	/* 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;
+
+	if (virtio_has_feature(vb->vdev, VIRTIO_BALLOON_F_REPORTING))
+		page_reporting_unregister(&vb->pr_dev_info);
+	if (virtio_has_feature(vb->vdev, VIRTIO_BALLOON_F_DEFLATE_ON_OOM))
+		unregister_oom_notifier(&vb->oom_nb);
+	if (virtio_has_feature(vb->vdev, VIRTIO_BALLOON_F_FREE_PAGE_HINT))
+		virtio_balloon_unregister_shrinker(vb);
+	spin_lock_irq(&vb->stop_update_lock);
+	vb->stop_update = true;
+	spin_unlock_irq(&vb->stop_update_lock);
+	cancel_work_sync(&vb->update_balloon_size_work);
+	cancel_work_sync(&vb->update_balloon_stats_work);
+
+	if (virtio_has_feature(vdev, VIRTIO_BALLOON_F_FREE_PAGE_HINT)) {
+		cancel_work_sync(&vb->report_free_page_work);
+		destroy_workqueue(vb->balloon_wq);
+	}
+
+	remove_common(vb);
+#ifdef CONFIG_BALLOON_COMPACTION
+	if (vb->vb_dev_info.inode)
+		iput(vb->vb_dev_info.inode);
+
+	kern_unmount(balloon_mnt);
+#endif
+	kfree(vb);
+}
+
+#ifdef CONFIG_PM_SLEEP
+static int virtballoon_freeze(struct virtio_device *vdev)
+{
+	struct virtio_balloon *vb = vdev->priv;
+
+	/*
+	 * The workqueue 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);
+
+	if (towards_target(vb))
+		virtballoon_changed(vdev);
+	update_balloon_size(vb);
+	return 0;
+}
+#endif
+
+static int virtballoon_validate(struct virtio_device *vdev)
+{
+	/*
+	 * Inform the hypervisor that our pages are poisoned or
+	 * initialized. If we cannot do that then we should disable
+	 * page reporting as it could potentially change the contents
+	 * of our free pages.
+	 */
+	if (!want_init_on_free() &&
+	    (IS_ENABLED(CONFIG_PAGE_POISONING_NO_SANITY) ||
+	     !page_poisoning_enabled()))
+		__virtio_clear_bit(vdev, VIRTIO_BALLOON_F_PAGE_POISON);
+	else if (!virtio_has_feature(vdev, VIRTIO_BALLOON_F_PAGE_POISON))
+		__virtio_clear_bit(vdev, VIRTIO_BALLOON_F_REPORTING);
+
+	__virtio_clear_bit(vdev, VIRTIO_F_ACCESS_PLATFORM);
+	return 0;
+}
+
+static unsigned int features[] = {
+	VIRTIO_BALLOON_F_MUST_TELL_HOST,
+	VIRTIO_BALLOON_F_STATS_VQ,
+	VIRTIO_BALLOON_F_DEFLATE_ON_OOM,
+	VIRTIO_BALLOON_F_FREE_PAGE_HINT,
+	VIRTIO_BALLOON_F_PAGE_POISON,
+	VIRTIO_BALLOON_F_REPORTING,
+};
+
+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,
+	.validate =	virtballoon_validate,
+	.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");