[RFC PATCH v5 00/26] 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 virtual address space to the
device to read and write into, and it maps new vrings and the guest
memory in it. SVQ 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.

Thanks of being a buffers relay system, SVQ can be used also to
communicate devices and drivers with different capabilities, like
devices that only supports packed vring and not split and old guest
with no driver packed support.

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.

SVQ needs to be enabled with QMP command:

{ "execute": "x-vhost-set-shadow-vq",
      "arguments": { "name": "vhost-vdpa0", "enable": true } }

This series includes some patches to delete in the final version that
helps with its testing. The first two of the series have been sent
sepparately but they haven't been included in qemu main branch.

The two after them adds the feature to stop the device and be able to
set and get its status. It's intended to be used with vp_vpda driver in
a nested environment, so they are also external to this series. The
vp_vdpa driver also need modifications to forward the new status bit,
they will be proposed sepparately

Patches 5-12 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 13-17, but with device to guest
notifications.

Based on them, patches from 18 to 22 implement the actual buffer
forwarding, using some features already introduced in previous.
However, they will need a host device with no iommu, something that
is not available at the moment.

The last part of the series uses properly the host iommu, so the driver
can access this new virtual address space created.

Comments are welcome.

TODO:
* Event, indirect, packed, and others features of virtio.
* 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.
* Support multiqueue virtio-net vdpa.
* Proper documentation.

Changes from v4 RFC:
* Support of allocating / freeing iova ranges in IOVA tree. Extending
  already present iova-tree for that.
* Proper validation of guest features. Now SVQ can negotiate a
  different set of features with the device when enabled.
* Support of host notifiers memory regions
* Handling of SVQ full queue in case guest's descriptors span to
  different memory regions (qemu's VA chunks).
* Flush pending used buffers at end of SVQ operation.
* QMP command now looks by NetClientState name. Other devices will need
  to implement it's way to enable vdpa.
* Rename QMP command to set, so it looks more like a way of working
* Better use of qemu error system
* Make a few assertions proper error-handling paths.
* Add more documentation
* Less coupling of virtio / vhost, that could cause friction on changes
* Addressed many other small comments and small fixes.

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 (26):
  util: Make some iova_tree parameters const
  vhost: Fix last queue index of devices with no cvq
  virtio: Add VIRTIO_F_QUEUE_STATE
  virtio-net: Honor VIRTIO_CONFIG_S_DEVICE_STOPPED
  vhost: Add x-vhost-set-shadow-vq qmp
  vhost: Add VhostShadowVirtqueue
  vdpa: Save kick_fd in vhost-vdpa
  vdpa: Add vhost_svq_get_dev_kick_notifier
  vdpa: Add vhost_svq_set_svq_kick_fd
  vhost: Add Shadow VirtQueue kick forwarding capabilities
  vhost: Handle host notifiers in SVQ
  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: ack VIRTIO_F_QUEUE_STATE if device supports it
  vhost: Add vhost_svq_valid_device_features to shadow vq
  vhost: Add vhost_svq_valid_guest_features to shadow vq
  vhost: Shadow virtqueue buffers forwarding
  util: Add iova_tree_alloc
  vhost: Add VhostIOVATree
  vhost: Use a tree to store memory mappings
  vdpa: Add custom IOTLB translations to SVQ

 qapi/net.json                                 |  20 +
 hw/virtio/vhost-iova-tree.h                   |  27 +
 hw/virtio/vhost-shadow-virtqueue.h            |  44 ++
 hw/virtio/virtio-pci.h                        |   1 +
 include/hw/virtio/vhost-vdpa.h                |  12 +
 include/hw/virtio/virtio.h                    |   4 +-
 include/qemu/iova-tree.h                      |  25 +-
 .../standard-headers/linux/virtio_config.h    |   5 +
 include/standard-headers/linux/virtio_pci.h   |   2 +
 hw/i386/intel_iommu.c                         |   2 +-
 hw/net/vhost_net.c                            |   2 +-
 hw/net/virtio-net.c                           |   6 +-
 hw/virtio/vhost-iova-tree.c                   | 157 ++++
 hw/virtio/vhost-shadow-virtqueue.c            | 746 ++++++++++++++++++
 hw/virtio/vhost-vdpa.c                        | 437 +++++++++-
 hw/virtio/virtio-pci.c                        |  16 +-
 net/vhost-vdpa.c                              |  28 +
 util/iova-tree.c                              | 151 +++-
 hw/virtio/meson.build                         |   2 +-
 19 files changed, 1664 insertions(+), 23 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