On Mon, 29 Jun 2020 11:57:14 -0400
"Michael S. Tsirkin" <m...@redhat.com> wrote:

> On Wed, Jun 17, 2020 at 12:43:57PM +0200, Pierre Morel wrote:
> > An architecture protecting the guest memory against unauthorized host
> > access may want to enforce VIRTIO I/O device protection through the
> > use of VIRTIO_F_IOMMU_PLATFORM.
> > 
> > Let's give a chance to the architecture to accept or not devices
> > without VIRTIO_F_IOMMU_PLATFORM.
> > 
> > Signed-off-by: Pierre Morel <pmo...@linux.ibm.com>
> > Acked-by: Jason Wang <jasow...@redhat.com>
> > Acked-by: Christian Borntraeger <borntrae...@de.ibm.com>
> > ---
> >  arch/s390/mm/init.c     |  6 ++++++
> >  drivers/virtio/virtio.c | 22 ++++++++++++++++++++++
> >  include/linux/virtio.h  |  2 ++
> >  3 files changed, 30 insertions(+)

> > @@ -179,6 +194,13 @@ int virtio_finalize_features(struct virtio_device *dev)
> >     if (!virtio_has_feature(dev, VIRTIO_F_VERSION_1))
> >             return 0;
> >  
> > +   if (arch_needs_virtio_iommu_platform(dev) &&
> > +           !virtio_has_feature(dev, VIRTIO_F_IOMMU_PLATFORM)) {
> > +           dev_warn(&dev->dev,
> > +                    "virtio: device must provide 
> > VIRTIO_F_IOMMU_PLATFORM\n");
> > +           return -ENODEV;
> > +   }
> > +
> >     virtio_add_status(dev, VIRTIO_CONFIG_S_FEATURES_OK);
> >     status = dev->config->get_status(dev);
> >     if (!(status & VIRTIO_CONFIG_S_FEATURES_OK)) {  
> 
> Well don't you need to check it *before* VIRTIO_F_VERSION_1, not after?

But it's only available with VERSION_1 anyway, isn't it? So it probably
also needs to fail when this feature is needed if VERSION_1 has not been
negotiated, I think.

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