Re: [PATCH v3 1/1] s390: virtio: let arch accept devices without IOMMU feature

[Pierre Morel]

On 2020-06-29 18:05, Cornelia Huck wrote:
> On Mon, 29 Jun 2020 11:57:14 -0400
> "Michael S. Tsirkin" <mst@xxxxxxxxxx> 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 <pmorel@xxxxxxxxxxxxx>
> > > Acked-by: Jason Wang <jasowang@xxxxxxxxxx>
> > > Acked-by: Christian Borntraeger <borntraeger@xxxxxxxxxx>
> > > ---
> > >   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.

Yes, clearly, I will add this.

Thanks,
Pierre

--
Pierre Morel
IBM Lab Boeblingen