[RFC PATCH v4 00/20] vDPA shadow virtqueue

[Eugenio Pérez]

This series enable shadow virtqueue (SVQ) for vhost-vdpa devices. This
is intended as a new method of tracking the memory the devices touch
during a migration process: Instead of relay on vhost device's dirty
logging capability, SVQ intercepts the VQ dataplane forwarding the
descriptors between VM and device. This way qemu is the effective
writer of guests memory, like in qemu's virtio device operation.

When SVQ is enabled qemu offers a new vring to the device to read
and write into, and also intercepts kicks and calls between the device
and the guest. Used buffers relay would cause dirty memory being
tracked, but at this RFC SVQ is not enabled on migration automatically.

It is based on the ideas of DPDK SW assisted LM, in the series of
DPDK's https://patchwork.dpdk.org/cover/48370/ . However, these does
not map the shadow vq in guest's VA, but in qemu's.

For qemu to use shadow virtqueues the guest virtio driver must not use
features like event_idx or indirect descriptors. These limitations will
be addressed in later series, but they are left out for simplicity at
the moment.

SVQ needs to be enabled with QMP command:

{ "execute": "x-vhost-enable-shadow-vq",
      "arguments": { "name": "dev0", "enable": true } }

This series includes some patches to delete in the final version that
helps with its testing. The first two of the series freely implements
the feature to stop the device and be able to retrieve its status. It's
intended to be used with vp_vpda driver in a nested environment. This
driver also need modifications to forward the new status bit.

Patches 2-8 prepares the SVQ and QMP command to support guest to host
notifications forwarding. If the SVQ is enabled with these ones
applied and the device supports it, that part can be tested in
isolation (for example, with networking), hopping through SVQ.

Same thing is true with patches 9-13, but with device to guest
notifications.

The rest of the patches implements the actual buffer forwarding.

Comments are welcome.

TODO:
* Event, indirect, packed, and others features of virtio - Waiting for
  confirmation of the big picture.
* Use already available iova tree to track mappings.
* To sepparate buffers forwarding in its own AIO context, so we can
  throw more threads to that task and we don't need to stop the main
  event loop.
* unmap iommu memory. Now the tree can only grow from SVQ enable, but
  it should be fine as long as not a lot of memory is added to the
  guest.
* Rebase on top of latest qemu (and, hopefully, on top of multiqueue
  vdpa).
* Some assertions need to be appropiate error handling paths.
* Proper documentation.

Changes from v3 RFC:
  * Move everything to vhost-vdpa backend. A big change, this allowed
    some cleanup but more code has been added in other places.
  * More use of glib utilities, especially to manage memory.
v3 link:
https://lists.nongnu.org/archive/html/qemu-devel/2021-05/msg06032.html

Changes from v2 RFC:
  * Adding vhost-vdpa devices support
  * Fixed some memory leaks pointed by different comments
v2 link:
https://lists.nongnu.org/archive/html/qemu-devel/2021-03/msg05600.html

Changes from v1 RFC:
  * Use QMP instead of migration to start SVQ mode.
  * Only accepting IOMMU devices, closer behavior with target devices
    (vDPA)
  * Fix invalid masking/unmasking of vhost call fd.
  * Use of proper methods for synchronization.
  * No need to modify VirtIO device code, all of the changes are
    contained in vhost code.
  * Delete superfluous code.
  * An intermediate RFC was sent with only the notifications forwarding
    changes. It can be seen in
    https://patchew.org/QEMU/20210129205415.876290-1-eperezma@redhat.com/
v1 link:
https://lists.gnu.org/archive/html/qemu-devel/2020-11/msg05372.html

Eugenio Pérez (20):
      virtio: Add VIRTIO_F_QUEUE_STATE
      virtio-net: Honor VIRTIO_CONFIG_S_DEVICE_STOPPED
      virtio: Add virtio_queue_is_host_notifier_enabled
      vhost: Make vhost_virtqueue_{start,stop} public
      vhost: Add x-vhost-enable-shadow-vq qmp
      vhost: Add VhostShadowVirtqueue
      vdpa: Register vdpa devices in a list
      vhost: Route guest->host notification through shadow virtqueue
      Add vhost_svq_get_svq_call_notifier
      Add vhost_svq_set_guest_call_notifier
      vdpa: Save call_fd in vhost-vdpa
      vhost-vdpa: Take into account SVQ in vhost_vdpa_set_vring_call
      vhost: Route host->guest notification through shadow virtqueue
      virtio: Add vhost_shadow_vq_get_vring_addr
      vdpa: Save host and guest features
      vhost: Add vhost_svq_valid_device_features to shadow vq
      vhost: Shadow virtqueue buffers forwarding
      vhost: Add VhostIOVATree
      vhost: Use a tree to store memory mappings
      vdpa: Add custom IOTLB translations to SVQ

Eugenio Pérez (20):
  virtio: Add VIRTIO_F_QUEUE_STATE
  virtio-net: Honor VIRTIO_CONFIG_S_DEVICE_STOPPED
  virtio: Add virtio_queue_is_host_notifier_enabled
  vhost: Make vhost_virtqueue_{start,stop} public
  vhost: Add x-vhost-enable-shadow-vq qmp
  vhost: Add VhostShadowVirtqueue
  vdpa: Register vdpa devices in a list
  vhost: Route guest->host notification through shadow virtqueue
  vdpa: Save call_fd in vhost-vdpa
  vhost-vdpa: Take into account SVQ in vhost_vdpa_set_vring_call
  vhost: Route host->guest notification through shadow virtqueue
  virtio: Add vhost_shadow_vq_get_vring_addr
  vdpa: Save host and guest features
  vhost: Add vhost_svq_valid_device_features to shadow vq
  vhost: Shadow virtqueue buffers forwarding
  vhost: Check for device VRING_USED_F_NO_NOTIFY at shadow virtqueue
    kick
  vhost: Use VRING_AVAIL_F_NO_INTERRUPT at device call on shadow
    virtqueue
  vhost: Add VhostIOVATree
  vhost: Use a tree to store memory mappings
  vdpa: Add custom IOTLB translations to SVQ

 qapi/net.json                                 |  23 +
 hw/virtio/vhost-iova-tree.h                   |  40 ++
 hw/virtio/vhost-shadow-virtqueue.h            |  37 ++
 hw/virtio/virtio-pci.h                        |   1 +
 include/hw/virtio/vhost-vdpa.h                |  13 +
 include/hw/virtio/vhost.h                     |   4 +
 include/hw/virtio/virtio.h                    |   5 +-
 .../standard-headers/linux/virtio_config.h    |   5 +
 include/standard-headers/linux/virtio_pci.h   |   2 +
 hw/net/virtio-net.c                           |   6 +-
 hw/virtio/vhost-iova-tree.c                   | 230 +++++++
 hw/virtio/vhost-shadow-virtqueue.c            | 619 ++++++++++++++++++
 hw/virtio/vhost-vdpa.c                        | 412 +++++++++++-
 hw/virtio/vhost.c                             |  12 +-
 hw/virtio/virtio-pci.c                        |  16 +-
 hw/virtio/virtio.c                            |   5 +
 hw/virtio/meson.build                         |   2 +-
 hw/virtio/trace-events                        |   1 +
 18 files changed, 1413 insertions(+), 20 deletions(-)
 create mode 100644 hw/virtio/vhost-iova-tree.h
 create mode 100644 hw/virtio/vhost-shadow-virtqueue.h
 create mode 100644 hw/virtio/vhost-iova-tree.c
 create mode 100644 hw/virtio/vhost-shadow-virtqueue.c

-- 
2.27.0