Adding upstream version 1:7.2+dfsg.upstream/1%7.2+dfsgupstream

Signed-off-by: Daniel Baumann <mail@daniel-baumann.ch>

1 files changed, 1079 insertions, 0 deletions

diff --git a/hw/virtio/virtio-balloon.c b/hw/virtio/virtio-balloon.c
new file mode 100644
index 00000000..73ac5eb6
--- /dev/null
+++ b/hw/virtio/virtio-balloon.c
@@ -0,0 +1,1079 @@
+/*
+ * Virtio Balloon Device
+ *
+ * Copyright IBM, Corp. 2008
+ * Copyright (C) 2011 Red Hat, Inc.
+ * Copyright (C) 2011 Amit Shah <amit.shah@redhat.com>
+ *
+ * Authors:
+ *  Anthony Liguori   <aliguori@us.ibm.com>
+ *
+ * This work is licensed under the terms of the GNU GPL, version 2.  See
+ * the COPYING file in the top-level directory.
+ *
+ */
+
+#include "qemu/osdep.h"
+#include "qemu/iov.h"
+#include "qemu/module.h"
+#include "qemu/timer.h"
+#include "qemu/madvise.h"
+#include "hw/virtio/virtio.h"
+#include "hw/mem/pc-dimm.h"
+#include "hw/qdev-properties.h"
+#include "hw/boards.h"
+#include "sysemu/balloon.h"
+#include "hw/virtio/virtio-balloon.h"
+#include "exec/address-spaces.h"
+#include "qapi/error.h"
+#include "qapi/qapi-events-machine.h"
+#include "qapi/visitor.h"
+#include "trace.h"
+#include "qemu/error-report.h"
+#include "migration/misc.h"
+#include "migration/migration.h"
+
+#include "hw/virtio/virtio-bus.h"
+#include "hw/virtio/virtio-access.h"
+
+#define BALLOON_PAGE_SIZE  (1 << VIRTIO_BALLOON_PFN_SHIFT)
+
+typedef struct PartiallyBalloonedPage {
+    ram_addr_t base_gpa;
+    unsigned long *bitmap;
+} PartiallyBalloonedPage;
+
+static void virtio_balloon_pbp_free(PartiallyBalloonedPage *pbp)
+{
+    if (!pbp->bitmap) {
+        return;
+    }
+    g_free(pbp->bitmap);
+    pbp->bitmap = NULL;
+}
+
+static void virtio_balloon_pbp_alloc(PartiallyBalloonedPage *pbp,
+                                     ram_addr_t base_gpa,
+                                     long subpages)
+{
+    pbp->base_gpa = base_gpa;
+    pbp->bitmap = bitmap_new(subpages);
+}
+
+static bool virtio_balloon_pbp_matches(PartiallyBalloonedPage *pbp,
+                                       ram_addr_t base_gpa)
+{
+    return pbp->base_gpa == base_gpa;
+}
+
+static bool virtio_balloon_inhibited(void)
+{
+    /*
+     * Postcopy cannot deal with concurrent discards,
+     * so it's special, as well as background snapshots.
+     */
+    return ram_block_discard_is_disabled() || migration_in_incoming_postcopy() ||
+            migration_in_bg_snapshot();
+}
+
+static void balloon_inflate_page(VirtIOBalloon *balloon,
+                                 MemoryRegion *mr, hwaddr mr_offset,
+                                 PartiallyBalloonedPage *pbp)
+{
+    void *addr = memory_region_get_ram_ptr(mr) + mr_offset;
+    ram_addr_t rb_offset, rb_aligned_offset, base_gpa;
+    RAMBlock *rb;
+    size_t rb_page_size;
+    int subpages;
+
+    /* XXX is there a better way to get to the RAMBlock than via a
+     * host address? */
+    rb = qemu_ram_block_from_host(addr, false, &rb_offset);
+    rb_page_size = qemu_ram_pagesize(rb);
+
+    if (rb_page_size == BALLOON_PAGE_SIZE) {
+        /* Easy case */
+
+        ram_block_discard_range(rb, rb_offset, rb_page_size);
+        /* We ignore errors from ram_block_discard_range(), because it
+         * has already reported them, and failing to discard a balloon
+         * page is not fatal */
+        return;
+    }
+
+    /* Hard case
+     *
+     * We've put a piece of a larger host page into the balloon - we
+     * need to keep track until we have a whole host page to
+     * discard
+     */
+    warn_report_once(
+"Balloon used with backing page size > 4kiB, this may not be reliable");
+
+    rb_aligned_offset = QEMU_ALIGN_DOWN(rb_offset, rb_page_size);
+    subpages = rb_page_size / BALLOON_PAGE_SIZE;
+    base_gpa = memory_region_get_ram_addr(mr) + mr_offset -
+               (rb_offset - rb_aligned_offset);
+
+    if (pbp->bitmap && !virtio_balloon_pbp_matches(pbp, base_gpa)) {
+        /* We've partially ballooned part of a host page, but now
+         * we're trying to balloon part of a different one.  Too hard,
+         * give up on the old partial page */
+        virtio_balloon_pbp_free(pbp);
+    }
+
+    if (!pbp->bitmap) {
+        virtio_balloon_pbp_alloc(pbp, base_gpa, subpages);
+    }
+
+    set_bit((rb_offset - rb_aligned_offset) / BALLOON_PAGE_SIZE,
+            pbp->bitmap);
+
+    if (bitmap_full(pbp->bitmap, subpages)) {
+        /* We've accumulated a full host page, we can actually discard
+         * it now */
+
+        ram_block_discard_range(rb, rb_aligned_offset, rb_page_size);
+        /* We ignore errors from ram_block_discard_range(), because it
+         * has already reported them, and failing to discard a balloon
+         * page is not fatal */
+        virtio_balloon_pbp_free(pbp);
+    }
+}
+
+static void balloon_deflate_page(VirtIOBalloon *balloon,
+                                 MemoryRegion *mr, hwaddr mr_offset)
+{
+    void *addr = memory_region_get_ram_ptr(mr) + mr_offset;
+    ram_addr_t rb_offset;
+    RAMBlock *rb;
+    size_t rb_page_size;
+    void *host_addr;
+    int ret;
+
+    /* XXX is there a better way to get to the RAMBlock than via a
+     * host address? */
+    rb = qemu_ram_block_from_host(addr, false, &rb_offset);
+    rb_page_size = qemu_ram_pagesize(rb);
+
+    host_addr = (void *)((uintptr_t)addr & ~(rb_page_size - 1));
+
+    /* When a page is deflated, we hint the whole host page it lives
+     * on, since we can't do anything smaller */
+    ret = qemu_madvise(host_addr, rb_page_size, QEMU_MADV_WILLNEED);
+    if (ret != 0) {
+        warn_report("Couldn't MADV_WILLNEED on balloon deflate: %s",
+                    strerror(errno));
+        /* Otherwise ignore, failing to page hint shouldn't be fatal */
+    }
+}
+
+static const char *balloon_stat_names[] = {
+   [VIRTIO_BALLOON_S_SWAP_IN] = "stat-swap-in",
+   [VIRTIO_BALLOON_S_SWAP_OUT] = "stat-swap-out",
+   [VIRTIO_BALLOON_S_MAJFLT] = "stat-major-faults",
+   [VIRTIO_BALLOON_S_MINFLT] = "stat-minor-faults",
+   [VIRTIO_BALLOON_S_MEMFREE] = "stat-free-memory",
+   [VIRTIO_BALLOON_S_MEMTOT] = "stat-total-memory",
+   [VIRTIO_BALLOON_S_AVAIL] = "stat-available-memory",
+   [VIRTIO_BALLOON_S_CACHES] = "stat-disk-caches",
+   [VIRTIO_BALLOON_S_HTLB_PGALLOC] = "stat-htlb-pgalloc",
+   [VIRTIO_BALLOON_S_HTLB_PGFAIL] = "stat-htlb-pgfail",
+   [VIRTIO_BALLOON_S_NR] = NULL
+};
+
+/*
+ * reset_stats - Mark all items in the stats array as unset
+ *
+ * This function needs to be called at device initialization and before
+ * updating to a set of newly-generated stats.  This will ensure that no
+ * stale values stick around in case the guest reports a subset of the supported
+ * statistics.
+ */
+static inline void reset_stats(VirtIOBalloon *dev)
+{
+    int i;
+    for (i = 0; i < VIRTIO_BALLOON_S_NR; dev->stats[i++] = -1);
+}
+
+static bool balloon_stats_supported(const VirtIOBalloon *s)
+{
+    VirtIODevice *vdev = VIRTIO_DEVICE(s);
+    return virtio_vdev_has_feature(vdev, VIRTIO_BALLOON_F_STATS_VQ);
+}
+
+static bool balloon_stats_enabled(const VirtIOBalloon *s)
+{
+    return s->stats_poll_interval > 0;
+}
+
+static void balloon_stats_destroy_timer(VirtIOBalloon *s)
+{
+    if (balloon_stats_enabled(s)) {
+        timer_free(s->stats_timer);
+        s->stats_timer = NULL;
+        s->stats_poll_interval = 0;
+    }
+}
+
+static void balloon_stats_change_timer(VirtIOBalloon *s, int64_t secs)
+{
+    timer_mod(s->stats_timer, qemu_clock_get_ms(QEMU_CLOCK_VIRTUAL) + secs * 1000);
+}
+
+static void balloon_stats_poll_cb(void *opaque)
+{
+    VirtIOBalloon *s = opaque;
+    VirtIODevice *vdev = VIRTIO_DEVICE(s);
+
+    if (s->stats_vq_elem == NULL || !balloon_stats_supported(s)) {
+        /* re-schedule */
+        balloon_stats_change_timer(s, s->stats_poll_interval);
+        return;
+    }
+
+    virtqueue_push(s->svq, s->stats_vq_elem, 0);
+    virtio_notify(vdev, s->svq);
+    g_free(s->stats_vq_elem);
+    s->stats_vq_elem = NULL;
+}
+
+static void balloon_stats_get_all(Object *obj, Visitor *v, const char *name,
+                                  void *opaque, Error **errp)
+{
+    Error *err = NULL;
+    VirtIOBalloon *s = VIRTIO_BALLOON(obj);
+    int i;
+
+    if (!visit_start_struct(v, name, NULL, 0, &err)) {
+        goto out;
+    }
+    if (!visit_type_int(v, "last-update", &s->stats_last_update, &err)) {
+        goto out_end;
+    }
+
+    if (!visit_start_struct(v, "stats", NULL, 0, &err)) {
+        goto out_end;
+    }
+    for (i = 0; i < VIRTIO_BALLOON_S_NR; i++) {
+        if (!visit_type_uint64(v, balloon_stat_names[i], &s->stats[i], &err)) {
+            goto out_nested;
+        }
+    }
+    visit_check_struct(v, &err);
+out_nested:
+    visit_end_struct(v, NULL);
+
+    if (!err) {
+        visit_check_struct(v, &err);
+    }
+out_end:
+    visit_end_struct(v, NULL);
+out:
+    error_propagate(errp, err);
+}
+
+static void balloon_stats_get_poll_interval(Object *obj, Visitor *v,
+                                            const char *name, void *opaque,
+                                            Error **errp)
+{
+    VirtIOBalloon *s = VIRTIO_BALLOON(obj);
+    visit_type_int(v, name, &s->stats_poll_interval, errp);
+}
+
+static void balloon_stats_set_poll_interval(Object *obj, Visitor *v,
+                                            const char *name, void *opaque,
+                                            Error **errp)
+{
+    VirtIOBalloon *s = VIRTIO_BALLOON(obj);
+    int64_t value;
+
+    if (!visit_type_int(v, name, &value, errp)) {
+        return;
+    }
+
+    if (value < 0) {
+        error_setg(errp, "timer value must be greater than zero");
+        return;
+    }
+
+    if (value > UINT32_MAX) {
+        error_setg(errp, "timer value is too big");
+        return;
+    }
+
+    if (value == s->stats_poll_interval) {
+        return;
+    }
+
+    if (value == 0) {
+        /* timer=0 disables the timer */
+        balloon_stats_destroy_timer(s);
+        return;
+    }
+
+    if (balloon_stats_enabled(s)) {
+        /* timer interval change */
+        s->stats_poll_interval = value;
+        balloon_stats_change_timer(s, value);
+        return;
+    }
+
+    /* create a new timer */
+    g_assert(s->stats_timer == NULL);
+    s->stats_timer = timer_new_ms(QEMU_CLOCK_VIRTUAL, balloon_stats_poll_cb, s);
+    s->stats_poll_interval = value;
+    balloon_stats_change_timer(s, 0);
+}
+
+static void virtio_balloon_handle_report(VirtIODevice *vdev, VirtQueue *vq)
+{
+    VirtIOBalloon *dev = VIRTIO_BALLOON(vdev);
+    VirtQueueElement *elem;
+
+    while ((elem = virtqueue_pop(vq, sizeof(VirtQueueElement)))) {
+        unsigned int i;
+
+        /*
+         * When we discard the page it has the effect of removing the page
+         * from the hypervisor itself and causing it to be zeroed when it
+         * is returned to us. So we must not discard the page if it is
+         * accessible by another device or process, or if the guest is
+         * expecting it to retain a non-zero value.
+         */
+        if (virtio_balloon_inhibited() || dev->poison_val) {
+            goto skip_element;
+        }
+
+        for (i = 0; i < elem->in_num; i++) {
+            void *addr = elem->in_sg[i].iov_base;
+            size_t size = elem->in_sg[i].iov_len;
+            ram_addr_t ram_offset;
+            RAMBlock *rb;
+
+            /*
+             * There is no need to check the memory section to see if
+             * it is ram/readonly/romd like there is for handle_output
+             * below. If the region is not meant to be written to then
+             * address_space_map will have allocated a bounce buffer
+             * and it will be freed in address_space_unmap and trigger
+             * and unassigned_mem_write before failing to copy over the
+             * buffer. If more than one bad descriptor is provided it
+             * will return NULL after the first bounce buffer and fail
+             * to map any resources.
+             */
+            rb = qemu_ram_block_from_host(addr, false, &ram_offset);
+            if (!rb) {
+                trace_virtio_balloon_bad_addr(elem->in_addr[i]);
+                continue;
+            }
+
+            /*
+             * For now we will simply ignore unaligned memory regions, or
+             * regions that overrun the end of the RAMBlock.
+             */
+            if (!QEMU_IS_ALIGNED(ram_offset | size, qemu_ram_pagesize(rb)) ||
+                (ram_offset + size) > qemu_ram_get_used_length(rb)) {
+                continue;
+            }
+
+            ram_block_discard_range(rb, ram_offset, size);
+        }
+
+skip_element:
+        virtqueue_push(vq, elem, 0);
+        virtio_notify(vdev, vq);
+        g_free(elem);
+    }
+}
+
+static void virtio_balloon_handle_output(VirtIODevice *vdev, VirtQueue *vq)
+{
+    VirtIOBalloon *s = VIRTIO_BALLOON(vdev);
+    VirtQueueElement *elem;
+    MemoryRegionSection section;
+
+    for (;;) {
+        PartiallyBalloonedPage pbp = {};
+        size_t offset = 0;
+        uint32_t pfn;
+
+        elem = virtqueue_pop(vq, sizeof(VirtQueueElement));
+        if (!elem) {
+            break;
+        }
+
+        while (iov_to_buf(elem->out_sg, elem->out_num, offset, &pfn, 4) == 4) {
+            unsigned int p = virtio_ldl_p(vdev, &pfn);
+            hwaddr pa;
+
+            pa = (hwaddr) p << VIRTIO_BALLOON_PFN_SHIFT;
+            offset += 4;
+
+            section = memory_region_find(get_system_memory(), pa,
+                                         BALLOON_PAGE_SIZE);
+            if (!section.mr) {
+                trace_virtio_balloon_bad_addr(pa);
+                continue;
+            }
+            if (!memory_region_is_ram(section.mr) ||
+                memory_region_is_rom(section.mr) ||
+                memory_region_is_romd(section.mr)) {
+                trace_virtio_balloon_bad_addr(pa);
+                memory_region_unref(section.mr);
+                continue;
+            }
+
+            trace_virtio_balloon_handle_output(memory_region_name(section.mr),
+                                               pa);
+            if (!virtio_balloon_inhibited()) {
+                if (vq == s->ivq) {
+                    balloon_inflate_page(s, section.mr,
+                                         section.offset_within_region, &pbp);
+                } else if (vq == s->dvq) {
+                    balloon_deflate_page(s, section.mr, section.offset_within_region);
+                } else {
+                    g_assert_not_reached();
+                }
+            }
+            memory_region_unref(section.mr);
+        }
+
+        virtqueue_push(vq, elem, 0);
+        virtio_notify(vdev, vq);
+        g_free(elem);
+        virtio_balloon_pbp_free(&pbp);
+    }
+}
+
+static void virtio_balloon_receive_stats(VirtIODevice *vdev, VirtQueue *vq)
+{
+    VirtIOBalloon *s = VIRTIO_BALLOON(vdev);
+    VirtQueueElement *elem;
+    VirtIOBalloonStat stat;
+    size_t offset = 0;
+
+    elem = virtqueue_pop(vq, sizeof(VirtQueueElement));
+    if (!elem) {
+        goto out;
+    }
+
+    if (s->stats_vq_elem != NULL) {
+        /* This should never happen if the driver follows the spec. */
+        virtqueue_push(vq, s->stats_vq_elem, 0);
+        virtio_notify(vdev, vq);
+        g_free(s->stats_vq_elem);
+    }
+
+    s->stats_vq_elem = elem;
+
+    /* Initialize the stats to get rid of any stale values.  This is only
+     * needed to handle the case where a guest supports fewer stats than it
+     * used to (ie. it has booted into an old kernel).
+     */
+    reset_stats(s);
+
+    while (iov_to_buf(elem->out_sg, elem->out_num, offset, &stat, sizeof(stat))
+           == sizeof(stat)) {
+        uint16_t tag = virtio_tswap16(vdev, stat.tag);
+        uint64_t val = virtio_tswap64(vdev, stat.val);
+
+        offset += sizeof(stat);
+        if (tag < VIRTIO_BALLOON_S_NR)
+            s->stats[tag] = val;
+    }
+    s->stats_vq_offset = offset;
+    s->stats_last_update = g_get_real_time() / G_USEC_PER_SEC;
+
+out:
+    if (balloon_stats_enabled(s)) {
+        balloon_stats_change_timer(s, s->stats_poll_interval);
+    }
+}
+
+static void virtio_balloon_handle_free_page_vq(VirtIODevice *vdev,
+                                               VirtQueue *vq)
+{
+    VirtIOBalloon *s = VIRTIO_BALLOON(vdev);
+    qemu_bh_schedule(s->free_page_bh);
+}
+
+static bool get_free_page_hints(VirtIOBalloon *dev)
+{
+    VirtQueueElement *elem;
+    VirtIODevice *vdev = VIRTIO_DEVICE(dev);
+    VirtQueue *vq = dev->free_page_vq;
+    bool ret = true;
+    int i;
+
+    while (dev->block_iothread) {
+        qemu_cond_wait(&dev->free_page_cond, &dev->free_page_lock);
+    }
+
+    elem = virtqueue_pop(vq, sizeof(VirtQueueElement));
+    if (!elem) {
+        return false;
+    }
+
+    if (elem->out_num) {
+        uint32_t id;
+        size_t size = iov_to_buf(elem->out_sg, elem->out_num, 0,
+                                 &id, sizeof(id));
+
+        virtio_tswap32s(vdev, &id);
+        if (unlikely(size != sizeof(id))) {
+            virtio_error(vdev, "received an incorrect cmd id");
+            ret = false;
+            goto out;
+        }
+        if (dev->free_page_hint_status == FREE_PAGE_HINT_S_REQUESTED &&
+            id == dev->free_page_hint_cmd_id) {
+            dev->free_page_hint_status = FREE_PAGE_HINT_S_START;
+        } else if (dev->free_page_hint_status == FREE_PAGE_HINT_S_START) {
+            /*
+             * Stop the optimization only when it has started. This
+             * avoids a stale stop sign for the previous command.
+             */
+            dev->free_page_hint_status = FREE_PAGE_HINT_S_STOP;
+        }
+    }
+
+    if (elem->in_num && dev->free_page_hint_status == FREE_PAGE_HINT_S_START) {
+        for (i = 0; i < elem->in_num; i++) {
+            qemu_guest_free_page_hint(elem->in_sg[i].iov_base,
+                                      elem->in_sg[i].iov_len);
+        }
+    }
+
+out:
+    virtqueue_push(vq, elem, 0);
+    g_free(elem);
+    return ret;
+}
+
+static void virtio_ballloon_get_free_page_hints(void *opaque)
+{
+    VirtIOBalloon *dev = opaque;
+    VirtIODevice *vdev = VIRTIO_DEVICE(dev);
+    VirtQueue *vq = dev->free_page_vq;
+    bool continue_to_get_hints;
+
+    do {
+        qemu_mutex_lock(&dev->free_page_lock);
+        virtio_queue_set_notification(vq, 0);
+        continue_to_get_hints = get_free_page_hints(dev);
+        qemu_mutex_unlock(&dev->free_page_lock);
+        virtio_notify(vdev, vq);
+      /*
+       * Start to poll the vq once the hinting started. Otherwise, continue
+       * only when there are entries on the vq, which need to be given back.
+       */
+    } while (continue_to_get_hints ||
+             dev->free_page_hint_status == FREE_PAGE_HINT_S_START);
+    virtio_queue_set_notification(vq, 1);
+}
+
+static bool virtio_balloon_free_page_support(void *opaque)
+{
+    VirtIOBalloon *s = opaque;
+    VirtIODevice *vdev = VIRTIO_DEVICE(s);
+
+    return virtio_vdev_has_feature(vdev, VIRTIO_BALLOON_F_FREE_PAGE_HINT);
+}
+
+static void virtio_balloon_free_page_start(VirtIOBalloon *s)
+{
+    VirtIODevice *vdev = VIRTIO_DEVICE(s);
+
+    qemu_mutex_lock(&s->free_page_lock);
+
+    if (s->free_page_hint_cmd_id == UINT_MAX) {
+        s->free_page_hint_cmd_id = VIRTIO_BALLOON_FREE_PAGE_HINT_CMD_ID_MIN;
+    } else {
+        s->free_page_hint_cmd_id++;
+    }
+
+    s->free_page_hint_status = FREE_PAGE_HINT_S_REQUESTED;
+    qemu_mutex_unlock(&s->free_page_lock);
+
+    virtio_notify_config(vdev);
+}
+
+static void virtio_balloon_free_page_stop(VirtIOBalloon *s)
+{
+    VirtIODevice *vdev = VIRTIO_DEVICE(s);
+
+    if (s->free_page_hint_status != FREE_PAGE_HINT_S_STOP) {
+        /*
+         * The lock also guarantees us that the
+         * virtio_ballloon_get_free_page_hints exits after the
+         * free_page_hint_status is set to S_STOP.
+         */
+        qemu_mutex_lock(&s->free_page_lock);
+        /*
+         * The guest isn't done hinting, so send a notification
+         * to the guest to actively stop the hinting.
+         */
+        s->free_page_hint_status = FREE_PAGE_HINT_S_STOP;
+        qemu_mutex_unlock(&s->free_page_lock);
+        virtio_notify_config(vdev);
+    }
+}
+
+static void virtio_balloon_free_page_done(VirtIOBalloon *s)
+{
+    VirtIODevice *vdev = VIRTIO_DEVICE(s);
+
+    if (s->free_page_hint_status != FREE_PAGE_HINT_S_DONE) {
+        /* See virtio_balloon_free_page_stop() */
+        qemu_mutex_lock(&s->free_page_lock);
+        s->free_page_hint_status = FREE_PAGE_HINT_S_DONE;
+        qemu_mutex_unlock(&s->free_page_lock);
+        virtio_notify_config(vdev);
+    }
+}
+
+static int
+virtio_balloon_free_page_hint_notify(NotifierWithReturn *n, void *data)
+{
+    VirtIOBalloon *dev = container_of(n, VirtIOBalloon, free_page_hint_notify);
+    VirtIODevice *vdev = VIRTIO_DEVICE(dev);
+    PrecopyNotifyData *pnd = data;
+
+    if (!virtio_balloon_free_page_support(dev)) {
+        /*
+         * This is an optimization provided to migration, so just return 0 to
+         * have the normal migration process not affected when this feature is
+         * not supported.
+         */
+        return 0;
+    }
+
+    /*
+     * Pages hinted via qemu_guest_free_page_hint() are cleared from the dirty
+     * bitmap and will not get migrated, especially also not when the postcopy
+     * destination starts using them and requests migration from the source; the
+     * faulting thread will stall until postcopy migration finishes and
+     * all threads are woken up. Let's not start free page hinting if postcopy
+     * is possible.
+     */
+    if (migrate_postcopy_ram()) {
+        return 0;
+    }
+
+    switch (pnd->reason) {
+    case PRECOPY_NOTIFY_BEFORE_BITMAP_SYNC:
+        virtio_balloon_free_page_stop(dev);
+        break;
+    case PRECOPY_NOTIFY_AFTER_BITMAP_SYNC:
+        if (vdev->vm_running) {
+            virtio_balloon_free_page_start(dev);
+            break;
+        }
+        /*
+         * Set S_DONE before migrating the vmstate, so the guest will reuse
+         * all hinted pages once running on the destination. Fall through.
+         */
+    case PRECOPY_NOTIFY_CLEANUP:
+        /*
+         * Especially, if something goes wrong during precopy or if migration
+         * is canceled, we have to properly communicate S_DONE to the VM.
+         */
+        virtio_balloon_free_page_done(dev);
+        break;
+    case PRECOPY_NOTIFY_SETUP:
+    case PRECOPY_NOTIFY_COMPLETE:
+        break;
+    default:
+        virtio_error(vdev, "%s: %d reason unknown", __func__, pnd->reason);
+    }
+
+    return 0;
+}
+
+static size_t virtio_balloon_config_size(VirtIOBalloon *s)
+{
+    uint64_t features = s->host_features;
+
+    if (s->qemu_4_0_config_size) {
+        return sizeof(struct virtio_balloon_config);
+    }
+    if (virtio_has_feature(features, VIRTIO_BALLOON_F_PAGE_POISON)) {
+        return sizeof(struct virtio_balloon_config);
+    }
+    if (virtio_has_feature(features, VIRTIO_BALLOON_F_FREE_PAGE_HINT)) {
+        return offsetof(struct virtio_balloon_config, poison_val);
+    }
+    return offsetof(struct virtio_balloon_config, free_page_hint_cmd_id);
+}
+
+static void virtio_balloon_get_config(VirtIODevice *vdev, uint8_t *config_data)
+{
+    VirtIOBalloon *dev = VIRTIO_BALLOON(vdev);
+    struct virtio_balloon_config config = {};
+
+    config.num_pages = cpu_to_le32(dev->num_pages);
+    config.actual = cpu_to_le32(dev->actual);
+    config.poison_val = cpu_to_le32(dev->poison_val);
+
+    if (dev->free_page_hint_status == FREE_PAGE_HINT_S_REQUESTED) {
+        config.free_page_hint_cmd_id =
+                       cpu_to_le32(dev->free_page_hint_cmd_id);
+    } else if (dev->free_page_hint_status == FREE_PAGE_HINT_S_STOP) {
+        config.free_page_hint_cmd_id =
+                       cpu_to_le32(VIRTIO_BALLOON_CMD_ID_STOP);
+    } else if (dev->free_page_hint_status == FREE_PAGE_HINT_S_DONE) {
+        config.free_page_hint_cmd_id =
+                       cpu_to_le32(VIRTIO_BALLOON_CMD_ID_DONE);
+    }
+
+    trace_virtio_balloon_get_config(config.num_pages, config.actual);
+    memcpy(config_data, &config, virtio_balloon_config_size(dev));
+}
+
+static int build_dimm_list(Object *obj, void *opaque)
+{
+    GSList **list = opaque;
+
+    if (object_dynamic_cast(obj, TYPE_PC_DIMM)) {
+        DeviceState *dev = DEVICE(obj);
+        if (dev->realized) { /* only realized DIMMs matter */
+            *list = g_slist_prepend(*list, dev);
+        }
+    }
+
+    object_child_foreach(obj, build_dimm_list, opaque);
+    return 0;
+}
+
+static ram_addr_t get_current_ram_size(void)
+{
+    GSList *list = NULL, *item;
+    ram_addr_t size = current_machine->ram_size;
+
+    build_dimm_list(qdev_get_machine(), &list);
+    for (item = list; item; item = g_slist_next(item)) {
+        Object *obj = OBJECT(item->data);
+        if (!strcmp(object_get_typename(obj), TYPE_PC_DIMM)) {
+            size += object_property_get_int(obj, PC_DIMM_SIZE_PROP,
+                                            &error_abort);
+        }
+    }
+    g_slist_free(list);
+
+    return size;
+}
+
+static bool virtio_balloon_page_poison_support(void *opaque)
+{
+    VirtIOBalloon *s = opaque;
+    VirtIODevice *vdev = VIRTIO_DEVICE(s);
+
+    return virtio_vdev_has_feature(vdev, VIRTIO_BALLOON_F_PAGE_POISON);
+}
+
+static void virtio_balloon_set_config(VirtIODevice *vdev,
+                                      const uint8_t *config_data)
+{
+    VirtIOBalloon *dev = VIRTIO_BALLOON(vdev);
+    struct virtio_balloon_config config;
+    uint32_t oldactual = dev->actual;
+    ram_addr_t vm_ram_size = get_current_ram_size();
+
+    memcpy(&config, config_data, virtio_balloon_config_size(dev));
+    dev->actual = le32_to_cpu(config.actual);
+    if (dev->actual != oldactual) {
+        qapi_event_send_balloon_change(vm_ram_size -
+                        ((ram_addr_t) dev->actual << VIRTIO_BALLOON_PFN_SHIFT));
+    }
+    dev->poison_val = 0;
+    if (virtio_balloon_page_poison_support(dev)) {
+        dev->poison_val = le32_to_cpu(config.poison_val);
+    }
+    trace_virtio_balloon_set_config(dev->actual, oldactual);
+}
+
+static uint64_t virtio_balloon_get_features(VirtIODevice *vdev, uint64_t f,
+                                            Error **errp)
+{
+    VirtIOBalloon *dev = VIRTIO_BALLOON(vdev);
+    f |= dev->host_features;
+    virtio_add_feature(&f, VIRTIO_BALLOON_F_STATS_VQ);
+
+    return f;
+}
+
+static void virtio_balloon_stat(void *opaque, BalloonInfo *info)
+{
+    VirtIOBalloon *dev = opaque;
+    info->actual = get_current_ram_size() - ((uint64_t) dev->actual <<
+                                             VIRTIO_BALLOON_PFN_SHIFT);
+}
+
+static void virtio_balloon_to_target(void *opaque, ram_addr_t target)
+{
+    VirtIOBalloon *dev = VIRTIO_BALLOON(opaque);
+    VirtIODevice *vdev = VIRTIO_DEVICE(dev);
+    ram_addr_t vm_ram_size = get_current_ram_size();
+
+    if (target > vm_ram_size) {
+        target = vm_ram_size;
+    }
+    if (target) {
+        dev->num_pages = (vm_ram_size - target) >> VIRTIO_BALLOON_PFN_SHIFT;
+        virtio_notify_config(vdev);
+    }
+    trace_virtio_balloon_to_target(target, dev->num_pages);
+}
+
+static int virtio_balloon_post_load_device(void *opaque, int version_id)
+{
+    VirtIOBalloon *s = VIRTIO_BALLOON(opaque);
+
+    if (balloon_stats_enabled(s)) {
+        balloon_stats_change_timer(s, s->stats_poll_interval);
+    }
+    return 0;
+}
+
+static const VMStateDescription vmstate_virtio_balloon_free_page_hint = {
+    .name = "virtio-balloon-device/free-page-report",
+    .version_id = 1,
+    .minimum_version_id = 1,
+    .needed = virtio_balloon_free_page_support,
+    .fields = (VMStateField[]) {
+        VMSTATE_UINT32(free_page_hint_cmd_id, VirtIOBalloon),
+        VMSTATE_UINT32(free_page_hint_status, VirtIOBalloon),
+        VMSTATE_END_OF_LIST()
+    }
+};
+
+static const VMStateDescription vmstate_virtio_balloon_page_poison = {
+    .name = "virtio-balloon-device/page-poison",
+    .version_id = 1,
+    .minimum_version_id = 1,
+    .needed = virtio_balloon_page_poison_support,
+    .fields = (VMStateField[]) {
+        VMSTATE_UINT32(poison_val, VirtIOBalloon),
+        VMSTATE_END_OF_LIST()
+    }
+};
+
+static const VMStateDescription vmstate_virtio_balloon_device = {
+    .name = "virtio-balloon-device",
+    .version_id = 1,
+    .minimum_version_id = 1,
+    .post_load = virtio_balloon_post_load_device,
+    .fields = (VMStateField[]) {
+        VMSTATE_UINT32(num_pages, VirtIOBalloon),
+        VMSTATE_UINT32(actual, VirtIOBalloon),
+        VMSTATE_END_OF_LIST()
+    },
+    .subsections = (const VMStateDescription * []) {
+        &vmstate_virtio_balloon_free_page_hint,
+        &vmstate_virtio_balloon_page_poison,
+        NULL
+    }
+};
+
+static void virtio_balloon_device_realize(DeviceState *dev, Error **errp)
+{
+    VirtIODevice *vdev = VIRTIO_DEVICE(dev);
+    VirtIOBalloon *s = VIRTIO_BALLOON(dev);
+    int ret;
+
+    virtio_init(vdev, VIRTIO_ID_BALLOON, virtio_balloon_config_size(s));
+
+    ret = qemu_add_balloon_handler(virtio_balloon_to_target,
+                                   virtio_balloon_stat, s);
+
+    if (ret < 0) {
+        error_setg(errp, "Only one balloon device is supported");
+        virtio_cleanup(vdev);
+        return;
+    }
+
+    if (virtio_has_feature(s->host_features, VIRTIO_BALLOON_F_FREE_PAGE_HINT) &&
+        !s->iothread) {
+        error_setg(errp, "'free-page-hint' requires 'iothread' to be set");
+        virtio_cleanup(vdev);
+        return;
+    }
+
+    s->ivq = virtio_add_queue(vdev, 128, virtio_balloon_handle_output);
+    s->dvq = virtio_add_queue(vdev, 128, virtio_balloon_handle_output);
+    s->svq = virtio_add_queue(vdev, 128, virtio_balloon_receive_stats);
+
+    if (virtio_has_feature(s->host_features, VIRTIO_BALLOON_F_FREE_PAGE_HINT)) {
+        s->free_page_vq = virtio_add_queue(vdev, VIRTQUEUE_MAX_SIZE,
+                                           virtio_balloon_handle_free_page_vq);
+        precopy_add_notifier(&s->free_page_hint_notify);
+
+        object_ref(OBJECT(s->iothread));
+        s->free_page_bh = aio_bh_new(iothread_get_aio_context(s->iothread),
+                                     virtio_ballloon_get_free_page_hints, s);
+    }
+
+    if (virtio_has_feature(s->host_features, VIRTIO_BALLOON_F_REPORTING)) {
+        s->reporting_vq = virtio_add_queue(vdev, 32,
+                                           virtio_balloon_handle_report);
+    }
+
+    reset_stats(s);
+}
+
+static void virtio_balloon_device_unrealize(DeviceState *dev)
+{
+    VirtIODevice *vdev = VIRTIO_DEVICE(dev);
+    VirtIOBalloon *s = VIRTIO_BALLOON(dev);
+
+    if (s->free_page_bh) {
+        qemu_bh_delete(s->free_page_bh);
+        object_unref(OBJECT(s->iothread));
+        virtio_balloon_free_page_stop(s);
+        precopy_remove_notifier(&s->free_page_hint_notify);
+    }
+    balloon_stats_destroy_timer(s);
+    qemu_remove_balloon_handler(s);
+
+    virtio_delete_queue(s->ivq);
+    virtio_delete_queue(s->dvq);
+    virtio_delete_queue(s->svq);
+    if (s->free_page_vq) {
+        virtio_delete_queue(s->free_page_vq);
+    }
+    if (s->reporting_vq) {
+        virtio_delete_queue(s->reporting_vq);
+    }
+    virtio_cleanup(vdev);
+}
+
+static void virtio_balloon_device_reset(VirtIODevice *vdev)
+{
+    VirtIOBalloon *s = VIRTIO_BALLOON(vdev);
+
+    if (virtio_balloon_free_page_support(s)) {
+        virtio_balloon_free_page_stop(s);
+    }
+
+    if (s->stats_vq_elem != NULL) {
+        virtqueue_unpop(s->svq, s->stats_vq_elem, 0);
+        g_free(s->stats_vq_elem);
+        s->stats_vq_elem = NULL;
+    }
+
+    s->poison_val = 0;
+}
+
+static void virtio_balloon_set_status(VirtIODevice *vdev, uint8_t status)
+{
+    VirtIOBalloon *s = VIRTIO_BALLOON(vdev);
+
+    if (!s->stats_vq_elem && vdev->vm_running &&
+        (status & VIRTIO_CONFIG_S_DRIVER_OK) && virtqueue_rewind(s->svq, 1)) {
+        /* poll stats queue for the element we have discarded when the VM
+         * was stopped */
+        virtio_balloon_receive_stats(vdev, s->svq);
+    }
+
+    if (virtio_balloon_free_page_support(s)) {
+        /*
+         * The VM is woken up and the iothread was blocked, so signal it to
+         * continue.
+         */
+        if (vdev->vm_running && s->block_iothread) {
+            qemu_mutex_lock(&s->free_page_lock);
+            s->block_iothread = false;
+            qemu_cond_signal(&s->free_page_cond);
+            qemu_mutex_unlock(&s->free_page_lock);
+        }
+
+        /* The VM is stopped, block the iothread. */
+        if (!vdev->vm_running) {
+            qemu_mutex_lock(&s->free_page_lock);
+            s->block_iothread = true;
+            qemu_mutex_unlock(&s->free_page_lock);
+        }
+    }
+}
+
+static void virtio_balloon_instance_init(Object *obj)
+{
+    VirtIOBalloon *s = VIRTIO_BALLOON(obj);
+
+    qemu_mutex_init(&s->free_page_lock);
+    qemu_cond_init(&s->free_page_cond);
+    s->free_page_hint_cmd_id = VIRTIO_BALLOON_FREE_PAGE_HINT_CMD_ID_MIN;
+    s->free_page_hint_notify.notify = virtio_balloon_free_page_hint_notify;
+
+    object_property_add(obj, "guest-stats", "guest statistics",
+                        balloon_stats_get_all, NULL, NULL, NULL);
+
+    object_property_add(obj, "guest-stats-polling-interval", "int",
+                        balloon_stats_get_poll_interval,
+                        balloon_stats_set_poll_interval,
+                        NULL, NULL);
+}
+
+static const VMStateDescription vmstate_virtio_balloon = {
+    .name = "virtio-balloon",
+    .minimum_version_id = 1,
+    .version_id = 1,
+    .fields = (VMStateField[]) {
+        VMSTATE_VIRTIO_DEVICE,
+        VMSTATE_END_OF_LIST()
+    },
+};
+
+static Property virtio_balloon_properties[] = {
+    DEFINE_PROP_BIT("deflate-on-oom", VirtIOBalloon, host_features,
+                    VIRTIO_BALLOON_F_DEFLATE_ON_OOM, false),
+    DEFINE_PROP_BIT("free-page-hint", VirtIOBalloon, host_features,
+                    VIRTIO_BALLOON_F_FREE_PAGE_HINT, false),
+    DEFINE_PROP_BIT("page-poison", VirtIOBalloon, host_features,
+                    VIRTIO_BALLOON_F_PAGE_POISON, true),
+    DEFINE_PROP_BIT("free-page-reporting", VirtIOBalloon, host_features,
+                    VIRTIO_BALLOON_F_REPORTING, false),
+    /* QEMU 4.0 accidentally changed the config size even when free-page-hint
+     * is disabled, resulting in QEMU 3.1 migration incompatibility.  This
+     * property retains this quirk for QEMU 4.1 machine types.
+     */
+    DEFINE_PROP_BOOL("qemu-4-0-config-size", VirtIOBalloon,
+                     qemu_4_0_config_size, false),
+    DEFINE_PROP_LINK("iothread", VirtIOBalloon, iothread, TYPE_IOTHREAD,
+                     IOThread *),
+    DEFINE_PROP_END_OF_LIST(),
+};
+
+static void virtio_balloon_class_init(ObjectClass *klass, void *data)
+{
+    DeviceClass *dc = DEVICE_CLASS(klass);
+    VirtioDeviceClass *vdc = VIRTIO_DEVICE_CLASS(klass);
+
+    device_class_set_props(dc, virtio_balloon_properties);
+    dc->vmsd = &vmstate_virtio_balloon;
+    set_bit(DEVICE_CATEGORY_MISC, dc->categories);
+    vdc->realize = virtio_balloon_device_realize;
+    vdc->unrealize = virtio_balloon_device_unrealize;
+    vdc->reset = virtio_balloon_device_reset;
+    vdc->get_config = virtio_balloon_get_config;
+    vdc->set_config = virtio_balloon_set_config;
+    vdc->get_features = virtio_balloon_get_features;
+    vdc->set_status = virtio_balloon_set_status;
+    vdc->vmsd = &vmstate_virtio_balloon_device;
+}
+
+static const TypeInfo virtio_balloon_info = {
+    .name = TYPE_VIRTIO_BALLOON,
+    .parent = TYPE_VIRTIO_DEVICE,
+    .instance_size = sizeof(VirtIOBalloon),
+    .instance_init = virtio_balloon_instance_init,
+    .class_init = virtio_balloon_class_init,
+};
+
+static void virtio_register_types(void)
+{
+    type_register_static(&virtio_balloon_info);
+}
+
+type_init(virtio_register_types)