linux-kernel - Re: [PATCH v1 0/2] vduse: add support for networking devices

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Message-ID: <20230704055840-mutt-send-email-mst@kernel.org>
Date:   Tue, 4 Jul 2023 05:59:28 -0400
From:   "Michael S. Tsirkin" <mst@...hat.com>
To:     Maxime Coquelin <maxime.coquelin@...hat.com>
Cc:     Jason Wang <jasowang@...hat.com>, xieyongji@...edance.com,
        david.marchand@...hat.com, lulu@...hat.com,
        linux-kernel@...r.kernel.org,
        virtualization@...ts.linux-foundation.org, netdev@...r.kernel.org,
        xuanzhuo@...ux.alibaba.com, eperezma@...hat.com
Subject: Re: [PATCH v1 0/2] vduse: add support for networking devices

On Tue, Jul 04, 2023 at 10:43:07AM +0200, Maxime Coquelin wrote:
> 
> 
> On 7/3/23 23:45, Michael S. Tsirkin wrote:
> > On Mon, Jul 03, 2023 at 09:43:49AM +0200, Maxime Coquelin wrote:
> > > 
> > > On 7/3/23 08:44, Jason Wang wrote:
> > > > On Sun, Jul 2, 2023 at 9:37 PM Michael S. Tsirkin <mst@...hat.com> wrote:
> > > > > 
> > > > > On Tue, Jun 27, 2023 at 01:36:50PM +0200, Maxime Coquelin wrote:
> > > > > > This small series enables virtio-net device type in VDUSE.
> > > > > > With it, basic operation have been tested, both with
> > > > > > virtio-vdpa and vhost-vdpa using DPDK Vhost library series
> > > > > > adding VDUSE support using split rings layout (merged in
> > > > > > DPDK v23.07-rc1).
> > > > > > 
> > > > > > Control queue support (and so multiqueue) has also been
> > > > > > tested, but requires a Kernel series from Jason Wang
> > > > > > relaxing control queue polling [1] to function reliably.
> > > > > > 
> > > > > > [1]: https://lore.kernel.org/lkml/CACGkMEtgrxN3PPwsDo4oOsnsSLJfEmBEZ0WvjGRr3whU+QasUg@mail.gmail.com/T/
> > > > > 
> > > > > Jason promised to post a new version of that patch.
> > > > > Right Jason?
> > > > 
> > > > Yes.
> > > > 
> > > > > For now let's make sure CVQ feature flag is off?
> > > > 
> > > > We can do that and relax on top of my patch.
> > > 
> > > I agree? Do you prefer a features negotiation, or failing init (like
> > > done for VERSION_1) if the VDUSE application advertises CVQ?
> > > 
> > > Thanks,
> > > Maxime
> > 
> > Unfortunately guests fail probe if feature set is inconsistent.
> > So I don't think passing through features is a good idea,
> > you need a list of legal bits. And when doing this,
> > clear CVQ and everything that depends on it.
> 
> Since this is temporary, while cvq is made more robust, I think it is
> better to fail VDUSE device creation if CVQ feature is advertised by the
> VDUSE application, instead of ensuring features depending on CVQ are
> also cleared.
> 
> Jason seems to think likewise, would that work for you?
> 
> Thanks,
> Maxime

Nothing is more permanent than temporary solutions.
My concern would be that hardware devices then start masking CVQ
intentionally just to avoid the pain of broken software.

> > 
> > 
> > > > Thanks
> > > > 
> > > > > 
> > > > > > RFC -> v1 changes:
> > > > > > ==================
> > > > > > - Fail device init if it does not support VERSION_1 (Jason)
> > > > > > 
> > > > > > Maxime Coquelin (2):
> > > > > >     vduse: validate block features only with block devices
> > > > > >     vduse: enable Virtio-net device type
> > > > > > 
> > > > > >    drivers/vdpa/vdpa_user/vduse_dev.c | 15 +++++++++++----
> > > > > >    1 file changed, 11 insertions(+), 4 deletions(-)
> > > > > > 
> > > > > > --
> > > > > > 2.41.0
> > > > > 
> > > > 
> >