linux-kernel - Re: [PATCH net-next v12 01/10] virtio

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Message-ID: <CACGkMEsfxXtHce2HeYwYxmhB0e5cOjn17qM6zFEt75bQhbtrDw@mail.gmail.com>
Date: Mon, 23 Jun 2025 16:07:00 +0800
From: Jason Wang <jasowang@...hat.com>
To: Yuri Benditovich <yuri.benditovich@...nix.com>
Cc: Akihiko Odaki <akihiko.odaki@...nix.com>, "Michael S. Tsirkin" <mst@...hat.com>, 
	Jonathan Corbet <corbet@....net>, Willem de Bruijn <willemdebruijn.kernel@...il.com>, 
	"David S. Miller" <davem@...emloft.net>, Eric Dumazet <edumazet@...gle.com>, 
	Jakub Kicinski <kuba@...nel.org>, Paolo Abeni <pabeni@...hat.com>, 
	Xuan Zhuo <xuanzhuo@...ux.alibaba.com>, Shuah Khan <shuah@...nel.org>, linux-doc@...r.kernel.org, 
	linux-kernel@...r.kernel.org, netdev@...r.kernel.org, kvm@...r.kernel.org, 
	virtualization@...ts.linux-foundation.org, linux-kselftest@...r.kernel.org, 
	Andrew Melnychenko <andrew@...nix.com>, Stephen Hemminger <stephen@...workplumber.org>, gur.stavi@...wei.com, 
	Lei Yang <leiyang@...hat.com>, Simon Horman <horms@...nel.org>
Subject: Re: [PATCH net-next v12 01/10] virtio_net: Add functions for hashing

On Mon, Jun 23, 2025 at 1:40 AM Yuri Benditovich
<yuri.benditovich@...nix.com> 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