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

[Jiri Pirko]

Mon, Mar 18, 2024 at 12:22:02PM CET, jonah.palmer@oracle.com wrote:
>
>
>On 3/16/24 11:45 AM, Jiri Pirko wrote:
>> 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!
>
>Hi Jiri! I think there are already kernel patches for
>VIRTIO_F_NOTIFICATION_DATA, unless you're referring to something more
>specific that wasn't included in these patches:
>
>[1]: virtio: add VIRTIO_F_NOTIFICATION_DATA feature support
>https://lore.kernel.org/lkml/20230324195029.2410503-1-viktor@daynix.com/
>
>[2]: virtio-vdpa: add VIRTIO_F_NOTIFICATION_DATA feature support
>https://lore.kernel.org/lkml/20230413081855.36643-3-alvaro.karsz@solid-run.com/

I missed this. Thx!

>
>Jonah