From mboxrd@z Thu Jan  1 00:00:00 1970
From: Cornelia Huck <cornelia.huck@de.ibm.com>
Subject: Re: [PATCH RFC v6 12/20] virtio: disallow late feature changes for
	virtio-1
Date: Fri, 12 Dec 2014 12:18:25 +0100
Message-ID: <20141212121825.6c09af4d.cornelia.huck@de.ibm.com>
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To: Thomas Huth <thuth@linux.vnet.ibm.com>
Cc: mst@redhat.com, qemu-devel@nongnu.org, virtualization@lists.linux-foundation.org
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On Fri, 12 Dec 2014 11:55:38 +0100
Thomas Huth <thuth@linux.vnet.ibm.com> wrote:

> On Thu, 11 Dec 2014 14:25:14 +0100
> Cornelia Huck <cornelia.huck@de.ibm.com> wrote:
> 
> > For virtio-1 devices, the driver must not attempt to set feature bits
> > after it set FEATURES_OK in the device status. Simply reject it in
> > that case.
> > 
> > Signed-off-by: Cornelia Huck <cornelia.huck@de.ibm.com>
> > ---
> >  hw/virtio/virtio.c         |   16 ++++++++++++++--
> >  include/hw/virtio/virtio.h |    2 ++
> >  2 files changed, 16 insertions(+), 2 deletions(-)
> > 
> > diff --git a/hw/virtio/virtio.c b/hw/virtio/virtio.c
> > index 57190ba..a3dd67b 100644
> > --- a/hw/virtio/virtio.c
> > +++ b/hw/virtio/virtio.c
> > @@ -978,7 +978,7 @@ void virtio_save(VirtIODevice *vdev, QEMUFile *f)
> >      vmstate_save_state(f, &vmstate_virtio, vdev);
> >  }
> > 
> > -int virtio_set_features(VirtIODevice *vdev, uint64_t val)
> > +static int __virtio_set_features(VirtIODevice *vdev, uint64_t val)
> 
> Maybe avoid the double underscores here? But unfortunately, I also fail
> to come up with a better suggestion for a name here ...

virtio_set_features_nocheck()?

This function is only called within virtio.c anyway...

> 
> >  {
> >      BusState *qbus = qdev_get_parent_bus(DEVICE(vdev));
> >      VirtioBusClass *vbusk = VIRTIO_BUS_GET_CLASS(qbus);
> > @@ -994,6 +994,18 @@ int virtio_set_features(VirtIODevice *vdev, uint64_t val)
> >      return bad ? -1 : 0;
> >  }
> > 
> > +int virtio_set_features(VirtIODevice *vdev, uint64_t val)
> > +{
> > +   /*
> > +     * The driver must not attempt to set features after feature negotiation
> > +     * has finished.
> > +     */
> > +    if (vdev->status & VIRTIO_CONFIG_S_FEATURES_OK) {
> > +        return -EINVAL;
> > +    }
> 
> Hmm, according to your patch description, the FEATURES_OK check only
> applies to virtio-1.0 devices ... so shouldn't there be a check for
> virtio-1 here? Or did I miss something?

A device in legacy mode will never have FEATURES_OK set. But it is a
bit non-obvious - maybe adding a check for VERSION_1 does not hurt.

> 
> > +    return __virtio_set_features(vdev, val);
> > +}
> 
>  Thomas