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From 92a638cb3b0601746d47b4a443762fe71bb21431 Mon Sep 17 00:00:00 2001
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From: Ladi Prosek <lprosek@redhat.com>
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Date: Thu, 10 Nov 2016 23:00:51 +0100
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Subject: [PATCH 8/8] virtio-balloon: fix stats vq migration
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RH-Author: Ladi Prosek <lprosek@redhat.com>
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Message-id: <1478797251-10302-2-git-send-email-lprosek@redhat.com>
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Patchwork-id: 72819
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O-Subject: [PATCH v2 8/6] virtio-balloon: fix stats vq migration
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Bugzilla: 1377968
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RH-Acked-by: Paolo Bonzini <pbonzini@redhat.com>
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RH-Acked-by: Michael S. Tsirkin <mst@redhat.com>
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RH-Acked-by: Miroslav Rezanina <mrezanin@redhat.com>
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The statistics virtqueue is not migrated properly because virtio-balloon
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does not include s->stats_vq_elem in the migration stream.
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After migration the statistics virtqueue hangs because the host never
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completes the last element (s->stats_vq_elem is NULL on the destination
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QEMU).  Therefore the guest never submits new elements and the virtqueue
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is hung.
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Instead of changing the migration stream format in an incompatible way,
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detect the migration case and rewind the virtqueue so the last element
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can be completed.
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Cc: Michael S. Tsirkin <mst@redhat.com>
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Cc: Roman Kagan <rkagan@virtuozzo.com>
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Cc: Stefan Hajnoczi <stefanha@redhat.com>
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Suggested-by: Roman Kagan <rkagan@virtuozzo.com>
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Signed-off-by: Ladi Prosek <lprosek@redhat.com>
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Reviewed-by: Stefan Hajnoczi <stefanha@redhat.com>
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Reviewed-by: Michael S. Tsirkin <mst@redhat.com>
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Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
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(cherry picked from commit 4a1e48becab81020adfb74b22c76a595f2d02a01)
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Signed-off-by: Ladi Prosek <lprosek@redhat.com>
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Signed-off-by: Miroslav Rezanina <mrezanin@redhat.com>
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---
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 hw/virtio/virtio-balloon.c | 13 +++++++++++++
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 1 file changed, 13 insertions(+)
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diff --git a/hw/virtio/virtio-balloon.c b/hw/virtio/virtio-balloon.c
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index faf93f7..1a60d3c 100644
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--- a/hw/virtio/virtio-balloon.c
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+++ b/hw/virtio/virtio-balloon.c
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@@ -403,6 +403,18 @@ static void virtio_balloon_device_reset(VirtIODevice *vdev)
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     }
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 }
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+static void virtio_balloon_set_status(VirtIODevice *vdev, uint8_t status)
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+{
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+    VirtIOBalloon *s = VIRTIO_BALLOON(vdev);
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+
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+    if (!s->stats_vq_elem_pending && vdev->vm_running &&
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+        (status & VIRTIO_CONFIG_S_DRIVER_OK) && virtqueue_rewind(s->svq, 1)) {
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+        /* poll stats queue for the element we have discarded when the VM
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+         * was stopped */
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+        virtio_balloon_receive_stats(vdev, s->svq);
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+    }
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+}
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+
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 static Property virtio_balloon_properties[] = {
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     DEFINE_PROP_END_OF_LIST(),
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 };
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@@ -419,6 +431,7 @@ static void virtio_balloon_class_init(ObjectClass *klass, void *data)
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     vdc->get_config = virtio_balloon_get_config;
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     vdc->set_config = virtio_balloon_set_config;
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     vdc->get_features = virtio_balloon_get_features;
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+    vdc->set_status = virtio_balloon_set_status;
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 }
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 static const TypeInfo virtio_balloon_info = {
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-- 
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1.8.3.1
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