Re: virtio-net: Unpermitted usage of virtqueue before virtio driver initialization

From: "Michael S. Tsirkin" <mst@redhat.com>
To: "Maciej Szymański" <maciej.szymanski@opensynergy.com>
Cc: Willem de Bruijn <willemb@google.com>,
	virtualization <virtualization@lists.linux-foundation.org>
Subject: Re: virtio-net: Unpermitted usage of virtqueue before virtio driver initialization
Date: Wed, 20 Apr 2022 07:10:49 -0400	[thread overview]
Message-ID: <20220420070944-mutt-send-email-mst@kernel.org> (raw)
In-Reply-To: <0a118236-bb98-9183-8be2-84f6b83e2581@opensynergy.com>

On Wed, Apr 20, 2022 at 10:17:27AM +0200, Maciej Szymański wrote:
> > > > > > Hmm so we have this:
> > > > > > 
> > > > > > 
> > > > > >          if ((dev->features ^ features) & NETIF_F_GRO_HW) {
> > > > > >                  if (vi->xdp_enabled)
> > > > > >                          return -EBUSY;
> > > > > > 
> > > > > >                  if (features & NETIF_F_GRO_HW)
> > > > > >                          offloads = vi->guest_offloads_capable;
> > > > > >                  else
> > > > > >                          offloads = vi->guest_offloads_capable &
> > > > > > ~GUEST_OFFLOAD_GRO_HW_MASK;
> > > > > > 
> > > > > >                  err = virtnet_set_guest_offloads(vi, offloads);
> > > > > >                  if (err)
> > > > > >                          return err;
> > > > > >                  vi->guest_offloads = offloads;
> > > > > >          }
> > > > > > 
> > > > > > which I guess should have prevented virtnet_set_guest_offloads
> > > > > > from ever running.
> > > > > > 
> > > > > >  From your description it sounds like you have observed this
> > > > > > in practice, right?
> > > > > > 
> > > Yes. I have proprietary virtio-net device which advertises following
> > > guest offload features :
> > > - VIRTIO_NET_F_GUEST_CSUM
> > > - VIRTIO_NET_F_GUEST_TSO4
> > > - VIRTIO_NET_F_GUEST_TSO6
> > > - VIRTIO_NET_F_GUEST_UFO
> > > 
> > > This feature set passes the condition in virtnet_set_features.

So why isn't dev->features equal to features?

-- 
MST

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