Re: [PATCH v1 0/1] s390: virtio-ccw: PV needs VIRTIO I/O device protection

[Cornelia Huck <cohuck@redhat.com>]

On Thu,  6 Aug 2020 16:23:01 +0200
Pierre Morel <pmorel@linux.ibm.com> wrote:

> Hi all,
> 
> In another series I proposed to add an architecture specific
> callback to fail feature negociation on architecture need.
> 
> In VIRTIO, we already have an entry to reject the features on the
> transport basis.
> 
> Transport is not architecture so I send a separate series in which
> we fail the feature negociation inside virtio_ccw_finalize_features,
> the virtio_config_ops.finalize_features for S390 CCW transport,
> when the device do not propose the VIRTIO_F_IOMMU_PLATFORM.
> 
> This solves the problem of crashing QEMU when this one is not using
> a CCW device with iommu_platform=on in S390.

This does work, and I'm tempted to queue this patch, but I'm wondering
whether we need to give up on a cross-architecture solution already
(especially keeping in mind that ccw is the only transport that is
really architecture-specific).

I know that we've gone through a few rounds already, and I'm not sure
whether we've been there already, but:

Could virtio_finalize_features() call an optional
arch_has_restricted_memory_access() function and do the enforcing of
IOMMU_PLATFORM? That would catch all transports, and things should work
once an architecture opts in. That direction also shouldn't be a
problem if virtio is a module.

> 
> Regards,
> Pierre
> 
> Regards,
> Pierre
> 
> Pierre Morel (1):
>   s390: virtio-ccw: PV needs VIRTIO I/O device protection
> 
>  drivers/s390/virtio/virtio_ccw.c | 24 +++++++++++++++++++-----
>  1 file changed, 19 insertions(+), 5 deletions(-)
>