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

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Date:   Wed, 10 Jun 2020 16:53:05 +0200
From:   Cornelia Huck <cohuck@...hat.com>
To:     Pierre Morel <pmorel@...ux.ibm.com>
Cc:     linux-kernel@...r.kernel.org, pasic@...ux.ibm.com,
        borntraeger@...ibm.com, frankja@...ux.ibm.com, mst@...hat.com,
        jasowang@...hat.com, kvm@...r.kernel.org,
        linux-s390@...r.kernel.org,
        virtualization@...ts.linux-foundation.org
Subject: Re: [PATCH] s390: protvirt: virtio: Refuse device without IOMMU

On Wed, 10 Jun 2020 16:37:55 +0200
Pierre Morel <pmorel@...ux.ibm.com> wrote:

> On 2020-06-10 15:24, Cornelia Huck wrote:
> > On Wed, 10 Jun 2020 15:11:51 +0200
> > Pierre Morel <pmorel@...ux.ibm.com> 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@...ux.ibm.com>
> >> ---
> >>   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))

Add a comment, and (maybe) a message?

Otherwise, I think this is fine, as it should fail the probe, which is
what we want.

> +               return -EIO;
> +
>          /* Give virtio_ring a chance to accept features. */
>          vring_transport_features(vdev);
> 
> 
> 
> Thanks,
> 
> Regards,
> Pierre
>