[RFC PATCH for 8.0 00/13] vDPA-net inflight descriptors migration with SVQ

[Eugenio Pérez]

The state of the descriptors (avail or used) may not be recoverable just
looking at the guest memory.  Out of order used descriptor may override
previous avail ones in the descriptor table or avail vring.

Currently we're not migrating this status in net devices because virtio-net,
vhost-kernel etc use the descriptors in order, so the information always
recoverable from guest's memory.  However, vDPA devices may use them out of
order, and other kind of devices like block need this support.

Shadow virtqueue is able to track these and resend them at the destination.
Add them to the virtio-net migration description so they are not lose in the
process.

This is a very early RFC just to validate the first draft so expect leftovers.
To fetch and request the descriptors from a device without SVQ need to be
implemented on top. Some other notable pending items are:
* Do not send the descriptors actually recoverable from the guest memory.
* Properly version the migrate data.
* Properly abstract the descriptors access from virtio-net to SVQ.
* Do not use VirtQueueElementOld but migrate directly VirtQueueElement.
* Replace lots of assertions with runtime conditionals.
* Other TODOs in the patch message or code changes.

Thanks.

Eugenio Pérez (13):
  vhost: add available descriptor list in SVQ
  vhost: iterate only available descriptors at SVQ stop
  vhost: merge avail list and next avail descriptors detach
  vhost: add vhost_svq_save_inflight
  virtio: Specify uint32_t as VirtQueueElementOld members type
  virtio: refactor qemu_get_virtqueue_element
  virtio: refactor qemu_put_virtqueue_element
  virtio: expose VirtQueueElementOld
  virtio: add vmstate_virtqueue_element_old
  virtio-net: Migrate vhost inflight descriptors
  virtio-net: save inflight descriptors at vhost shutdown
  vhost: expose vhost_svq_add_element
  vdpa: Recover inflight descriptors

 hw/virtio/vhost-shadow-virtqueue.h |   9 ++
 include/hw/virtio/virtio-net.h     |   2 +
 include/hw/virtio/virtio.h         |  32 ++++++
 include/migration/vmstate.h        |  22 ++++
 hw/net/vhost_net.c                 |  56 ++++++++++
 hw/net/virtio-net.c                | 129 +++++++++++++++++++++++
 hw/virtio/vhost-shadow-virtqueue.c |  52 +++++++--
 hw/virtio/vhost-vdpa.c             |  11 --
 hw/virtio/virtio.c                 | 162 ++++++++++++++++++-----------
 9 files changed, 392 insertions(+), 83 deletions(-)

-- 
2.31.1