netdev - Re: [PATCH v2] virtio_net: CTRL_GUEST_OFFLOADS depends on CTRL

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Message-ID: <20200110011236-mutt-send-email-mst@kernel.org>
Date:   Fri, 10 Jan 2020 01:12:56 -0500
From:   "Michael S. Tsirkin" <mst@...hat.com>
To:     David Miller <davem@...emloft.net>
Cc:     linux-kernel@...r.kernel.org, adelva@...gle.com,
        willemdebruijn.kernel@...il.com, jasowang@...hat.com,
        virtualization@...ts.linux-foundation.org, netdev@...r.kernel.org
Subject: Re: [PATCH v2] virtio_net: CTRL_GUEST_OFFLOADS depends on CTRL_VQ

On Thu, Jan 09, 2020 at 06:33:39PM -0800, David Miller wrote:
> From: "Michael S. Tsirkin" <mst@...hat.com>
> Date: Sun, 5 Jan 2020 08:22:07 -0500
> 
> > The only way for guest to control offloads (as enabled by
> > VIRTIO_NET_F_CTRL_GUEST_OFFLOADS) is by sending commands
> > through CTRL_VQ. So it does not make sense to
> > acknowledge VIRTIO_NET_F_CTRL_GUEST_OFFLOADS without
> > VIRTIO_NET_F_CTRL_VQ.
> > 
> > The spec does not outlaw devices with such a configuration, so we have
> > to support it. Simply clear VIRTIO_NET_F_CTRL_GUEST_OFFLOADS.
> > Note that Linux is still crashing if it tries to
> > change the offloads when there's no control vq.
> > That needs to be fixed by another patch.
> > 
> > Reported-by: Alistair Delva <adelva@...gle.com>
> > Reported-by: Willem de Bruijn <willemdebruijn.kernel@...il.com>
> > Fixes: 3f93522ffab2 ("virtio-net: switch off offloads on demand if possible on XDP set")
> > Signed-off-by: Michael S. Tsirkin <mst@...hat.com>
> > ---
> > 
> > Same patch as v1 but update documentation so it's clear it's not
> > enough to fix the crash.
> 
> Where are we with this patch?  There seems to still be some unresolved
> discussion about how we should actually handle this case.
> 
> Thanks.

Once discussion is resolved I'll post v3 with updated commit log.