Re: [PATCH v3 for 9.1 0/6] virtio, vhost: Add VIRTIO_F_NOTIFICATION_DATA support

[Jiri Pirko <jiri@resnulli.us>]

Fri, Mar 15, 2024 at 05:55:51PM CET, jonah.palmer@oracle.com wrote:
>The goal of these patches are to add support to a variety of virtio and
>vhost devices for the VIRTIO_F_NOTIFICATION_DATA transport feature. This
>feature indicates that a driver will pass extra data (instead of just a
>virtqueue's index) when notifying the corresponding device.
>
>The data passed in by the driver when this feature is enabled varies in
>format depending on if the device is using a split or packed virtqueue
>layout:
>
> Split VQ
>  - Upper 16 bits: shadow_avail_idx
>  - Lower 16 bits: virtqueue index
>
> Packed VQ
>  - Upper 16 bits: 1-bit wrap counter & 15-bit shadow_avail_idx
>  - Lower 16 bits: virtqueue index
>
>Also, due to the limitations of ioeventfd not being able to carry the
>extra provided by the driver, having both VIRTIO_F_NOTIFICATION_DATA
>feature and ioeventfd enabled is a functional mismatch. The user must
>explicitly disable ioeventfd for the device in the Qemu arguments when
>using this feature, else the device will fail to complete realization.
>
>For example, a device must explicitly enable notification_data as well
>as disable ioeventfd:
>
>    -device virtio-scsi-pci,...,ioeventfd=off,notification_data=on
>
>A significant aspect of this effort has been to maintain compatibility
>across different backends. As such, the feature is offered by backend
>devices only when supported, with fallback mechanisms where backend
>support is absent.
>
>v3: Validate VQ idx via. virtio_queue_get_num() (pci, mmio, ccw)
>    Rename virtio_queue_set_shadow_avail_data
>    Only pass in upper 16 bits of 32-bit extra data (was redundant)
>    Make notification compatibility check function static
>    Drop tags on patches 1/6, 3/6, and 4/6
>
>v2: Don't disable ioeventfd by default, user must disable it
>    Drop tags on patch 2/6
>
>Jonah Palmer (6):
>  virtio/virtio-pci: Handle extra notification data
>  virtio: Prevent creation of device using notification-data with ioeventfd
>  virtio-mmio: Handle extra notification data
>  virtio-ccw: Handle extra notification data
>  vhost/vhost-user: Add VIRTIO_F_NOTIFICATION_DATA to vhost feature bits
>  virtio: Add VIRTIO_F_NOTIFICATION_DATA property definition

Jonah, do you have kernel patches to add this feature as well?

Thanks!