qemu

virtio-balloon.c (34649B)

---

 /*
  * 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)