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

[Jonah Palmer <jonah.palmer@oracle.com>]

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/

Jonah