If something goes wrong during precopy, before stopping the VM, we will
never send a S_DONE indication to the VM, resulting in the hinted pages
not getting released to be used by the guest OS (e.g., Linux).
Easy to reproduce:
1. Start migration (e.g., HMP "migrate -d 'exec:gzip -c > STATEFILE.gz'")
2. Cancel migration (e.g., HMP "migrate_cancel")
3. Oberve in the guest (e.g., cat /proc/meminfo) that there is basically
no free memory left.
While at it, add similar locking to virtio_balloon_free_page_done() as
done in virtio_balloon_free_page_stop. Locking is still weird, but that
has to be sorted out separately.
There is nothing to do in the PRECOPY_NOTIFY_COMPLETE case. Add some
comments regarding S_DONE handling.
Fixes: c13c4153f76d ("virtio-balloon: VIRTIO_BALLOON_F_FREE_PAGE_HINT")
Reviewed-by: Alexander Duyck <alexander.h.du...@linux.intel.com>
Cc: Wei Wang <wei.w.w...@intel.com>
Cc: Alexander Duyck <alexander.du...@gmail.com>
Signed-off-by: David Hildenbrand <da...@redhat.com>
---
hw/virtio/virtio-balloon.c | 26 ++++++++++++++++++++------
1 file changed, 20 insertions(+), 6 deletions(-)
diff --git a/hw/virtio/virtio-balloon.c b/hw/virtio/virtio-balloon.c
index 10507b2a43..8a84718490 100644
--- a/hw/virtio/virtio-balloon.c
+++ b/hw/virtio/virtio-balloon.c
@@ -628,8 +628,13 @@ static void virtio_balloon_free_page_done(VirtIOBalloon *s)
{
VirtIODevice *vdev = VIRTIO_DEVICE(s);
- s->free_page_report_status = FREE_PAGE_REPORT_S_DONE;
- virtio_notify_config(vdev);
+ if (s->free_page_report_status != FREE_PAGE_REPORT_S_DONE) {
+ /* See virtio_balloon_free_page_stop() */
+ qemu_mutex_lock(&s->free_page_lock);
+ s->free_page_report_status = FREE_PAGE_REPORT_S_DONE;
+ qemu_mutex_unlock(&s->free_page_lock);
+ virtio_notify_config(vdev);
+ }
}
static int
@@ -653,17 +658,26 @@ virtio_balloon_free_page_report_notify(NotifierWithReturn
*n, void *data)
case PRECOPY_NOTIFY_SETUP:
precopy_enable_free_page_optimization();
break;
- case PRECOPY_NOTIFY_COMPLETE:
- case PRECOPY_NOTIFY_CLEANUP:
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);
- } else {
- virtio_balloon_free_page_done(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_COMPLETE:
break;
default:
virtio_error(vdev, "%s: %d reason unknown", __func__, pnd->reason);
--
2.26.2
