Re: [RFC PATCH v4 00/20] vDPA shadow virtqueue

[Jason Wang <jasowang@redhat.com>]

在 2021/10/1 下午3:05, Eugenio Pérez 写道:
> 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.


Hi Eugenio:


It would be helpful to have a public git repo for us to ease the review.

Thanks


>
> 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
>