Re: [PATCH net-next v12 01/10] virtio_net: Add functions for hashing

[Jason Wang]

On Mon, Jun 23, 2025 at 1:40 AM Yuri Benditovich
<yuri.benditovich@xxxxxxxxxx> wrote:
>
> > Yuri, can you help to clarify this?
>
> I see here several questions:
> 1. Whether it is ok for the device not to indicate support for XXX_EX hash type?
> - I think, yes (strictly speaking, it was better to test that before
> submitting the patches )
> 2. Is it possible that the guest will enable some XXX_EX hash type if
> the device does not indicate that it is supported?
> - No (I think this is part of the spec)

There's another question, is the device allowed to fallback to
VIRTIO_NET_HASH_TYPE_IPv6 if it fails to parse extensions?

> 3. What to do if we migrate between systems with different
> capabilities of hash support/reporting/whatever
> - IMO, at this moment such case should be excluded and only mechanism
> we have for that is the compatible machine version
> - in some future the change of device capabilities can be communicated
> to the driver and _probably_ the driver might be able to communicate
> the change of device capabilities to the OS

Are you suggesting implementing all hash types? Note that Akihiko
raises the issue that in the actual implementation there should be a
limitation of the maximum number of options. If such a limitation is
different between src and dst, the difference could be noticed by the
guest.

> 4. Does it make sense to have fine configuration of hash types mask
> via command-line?
> - IMO, no. This would require the user to have too much knowledge
> about RSS internals
>
> Please let me know if I missed something.
>

Thanks