Re: [PATCH] s390: protvirt: virtio: Refuse device without IOMMU

[Pierre Morel]

On 2020-06-10 15:24, Cornelia Huck wrote:
> On Wed, 10 Jun 2020 15:11:51 +0200
> Pierre Morel <pmorel@xxxxxxxxxxxxx> wrote:
>
> > Protected Virtualisation protects the memory of the guest and
> > do not allow a the host to access all of its memory.
> >
> > Let's refuse a VIRTIO device which does not use IOMMU
> > protected access.
> >
> > Signed-off-by: Pierre Morel <pmorel@xxxxxxxxxxxxx>
> > ---
> >   drivers/s390/virtio/virtio_ccw.c | 5 +++++
> >   1 file changed, 5 insertions(+)
> >
> > diff --git a/drivers/s390/virtio/virtio_ccw.c b/drivers/s390/virtio/virtio_ccw.c
> > index 5730572b52cd..06ffbc96587a 100644
> > --- a/drivers/s390/virtio/virtio_ccw.c
> > +++ b/drivers/s390/virtio/virtio_ccw.c
> > @@ -986,6 +986,11 @@ static void virtio_ccw_set_status(struct virtio_device *vdev, u8 status)
> >   	if (!ccw)
> >   		return;
> >   
> > +	/* Protected Virtualisation guest needs IOMMU */
> > +	if (is_prot_virt_guest() &&
> > +	    !__virtio_test_bit(vdev, VIRTIO_F_IOMMU_PLATFORM))
> > +			status &= ~VIRTIO_CONFIG_S_FEATURES_OK;
> > +
>
> set_status seems like an odd place to look at features; shouldn't that
> rather be done in finalize_features?

Right, looks better to me too.
What about:



diff --git a/drivers/s390/virtio/virtio_ccw.c 
b/drivers/s390/virtio/virtio_ccw.c
index 06ffbc96587a..227676297ea0 100644
--- a/drivers/s390/virtio/virtio_ccw.c
+++ b/drivers/s390/virtio/virtio_ccw.c
@@ -833,6 +833,11 @@ static int virtio_ccw_finalize_features(struct 
virtio_device *vdev)
                ret = -ENOMEM;
                goto out_free;
        }
+
+       if (is_prot_virt_guest() &&
+           !__virtio_test_bit(vdev, VIRTIO_F_IOMMU_PLATFORM))
+               return -EIO;
+
        /* Give virtio_ring a chance to accept features. */
        vring_transport_features(vdev);



Thanks,

Regards,
Pierre

--
Pierre Morel
IBM Lab Boeblingen