[RFC PATCH 00/12] Prefer to use SVQ to stall dataplane at NIC state restore through CVQ

["Eugenio Pérez" <eperezma@redhat.com>]

At this moment the migration of net features that depends on CVQ is not
possible, as there is no reliable way to restore the device state like mac
address, number of enabled queues, etc to the destination.  This is mainly
caused because the device must only read CVQ, and process all the commands
before resuming the dataplane.

This series uses the VirtIO feature _F_RING_RESET to achieve it, adding an
alternative method to late vq enabling proposed in [1][2].  It expose SVQ to
the device until it process all the CVQ messages, and then replaces the vring
for the guest's one.

As an advantage, it uses a feature well deviced in the VirtIO standard.  As a
disadvantage, current HW already support the late enabling and it does not
support RING_RESET.

This patch must be applied on top of the series ("Enable vdpa net migration
with features depending on CVQ") [1][2].

The patch has been tested with vp_vdpa, but using high IOVA instead of a
sepparated ID for shadow CVQ and shadow temporal vrings.

[1] Message-id: <20230706191227.835526-1-eperezma@redhat.com>
[2] https://lists.nongnu.org/archive/html/qemu-devel/2023-07/msg01325.html

Eugenio Pérez (12):
  vhost: add vhost_reset_queue_op
  vhost: add vhost_restart_queue_op
  vhost_net: Use ops->vhost_restart_queue in vhost_net_virtqueue_restart
  vhost_net: Use ops->vhost_reset_queue in vhost_net_virtqueue_reset
  vdpa: add vhost_vdpa_set_vring_ready_internal
  vdpa: add vhost_vdpa_svq_stop
  vdpa: add vhost_vdpa_reset_queue
  vdpa: add vhost_vdpa_svq_start
  vdpa: add vhost_vdpa_restart_queue
  vdpa: enable all vqs if the device support RING_RESET feature
  vdpa: use SVQ to stall dataplane while NIC state is being restored
  vhost: Allow _F_RING_RESET with shadow virtqueue

 include/hw/virtio/vhost-backend.h  |   6 ++
 hw/net/vhost_net.c                 |  16 ++--
 hw/virtio/vhost-shadow-virtqueue.c |   1 +
 hw/virtio/vhost-vdpa.c             | 139 +++++++++++++++++++++--------
 net/vhost-vdpa.c                   |  55 ++++++++++--
 hw/virtio/trace-events             |   2 +-
 6 files changed, 171 insertions(+), 48 deletions(-)

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2.39.3