RE: [PATCH v1] virtio-net: Fix to avoid using reserved feature bits

> From: Paolo Abeni <[email protected]>
> Sent: Monday, May 19, 2025 2:28 PM
> 
> On 5/7/25 11:57 AM, Paolo Abeni wrote:
> > On 5/6/25 6:20 PM, Parav Pandit wrote:
> >> From: Paolo Abeni <[email protected] Sent: Tuesday, May 6, 2025 9:10
> >> PM
> >>> On 5/6/25 5:00 PM, Parav Pandit wrote:
> >>>> From: Paolo Abeni <[email protected] Sent: Tuesday, May 6, 2025
> >>>> 8:09 PM
> >>>>> On 5/6/25 10:56 AM, Parav Pandit wrote:
> >>>>>> Are you good with #3?
> >>>>>
> >>>>> I'm sorry for the latency. Let me double check to avoid possible
> >>>>> misunderstanding; #3 means:
> >>>>>
> >>>>> - 0 to 23, and 50 to 127 Feature bits for the specific device type
> >>>>> + 0 to 23, and 45 to 127 Feature bits for the specific device type
> >>>>>
> >>>> No change in above feature bits.
> >>>>
> >>>>> using bits 46-39 for UDP tunnel offloads and likely bit 45 for
> >>>>> VIRTIO_NET_F_OUT_NET_HEADER.
> >>>>>
> >>>> This also to use bit 69 as proposed.
> >>>>
> >>>>> The VIRTIO_NET_F_CTRL_GUEST_OFFLOADS mapping should be
> specified
> >>>>> after eventually a new offload feature will be defined using a bit >= 64.
> >>>>>
> >>>> No. UDP tunnel feature bits 65 to 68 maps to command bits
> 46,47,48,49.
> >>>> This is the only description change in
> >>> VIRTIO_NET_F_CTRL_GUEST_OFFLOADS command.
> >>>> Would it work?
> >>>
> >>> AFAICT, yes, it should work.
> >>>
> >>> But it will not avoid the immediate need to expand the virtio
> >>> features negotiation above 64 bits, with the already mentioned
> complexity.
> >>>
> >>> I would preferably avoid that, if possible: I restarted this thread
> >>> with such a goal.
> >>>
> >> In that case we should adopt #2.
> >
> > Do we have quorum? Should I send a patch?
> 
> As per off-list discussion with Michel, there is no agreement on reserved bits
> re-use.
> 
> That means the only available option is #3 above.
> 
> @Parav, would you send a patch to fix the offloads <> features mapping, or do
> you prefer I'll do it?
> 
If its urgent, please do it.
If it can wait till 22 May this week, I will prepare one.

> Thanks,
> 
> Paolo