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

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Date:   Thu, 09 Jan 2020 18:33:39 -0800 (PST)
From:   David Miller <davem@...emloft.net>
To:     mst@...hat.com
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

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.