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

[Pierre Morel]

On 2020-06-29 17:57, Michael S. Tsirkin 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(+)
> >
> > diff --git a/arch/s390/mm/init.c b/arch/s390/mm/init.c
> > index 6dc7c3b60ef6..215070c03226 100644
> > --- a/arch/s390/mm/init.c
> > +++ b/arch/s390/mm/init.c
> > @@ -45,6 +45,7 @@
> >   #include <asm/kasan.h>
> >   #include <asm/dma-mapping.h>
> >   #include <asm/uv.h>
> > +#include <linux/virtio.h>
> >   
> >   pgd_t swapper_pg_dir[PTRS_PER_PGD] __section(.bss..swapper_pg_dir);
> >   
> > @@ -161,6 +162,11 @@ bool force_dma_unencrypted(struct device *dev)
> >   	return is_prot_virt_guest();
> >   }
> >   
> > +int arch_needs_virtio_iommu_platform(struct virtio_device *dev)
> > +{
> > +	return is_prot_virt_guest();
> > +}
> > +
> >   /* protected virtualization */
> >   static void pv_init(void)
> >   {
> > diff --git a/drivers/virtio/virtio.c b/drivers/virtio/virtio.c
> > index a977e32a88f2..aa8e01104f86 100644
> > --- a/drivers/virtio/virtio.c
> > +++ b/drivers/virtio/virtio.c
> > @@ -167,6 +167,21 @@ void virtio_add_status(struct virtio_device *dev, unsigned int status)
> >   }
> >   EXPORT_SYMBOL_GPL(virtio_add_status);
> >   
> > +/*
> > + * arch_needs_virtio_iommu_platform - provide arch specific hook when finalizing
> > + *				      features for VIRTIO device dev
> > + * @dev: the VIRTIO device being added
> > + *
> > + * Permits the platform to provide architecture specific functionality when
> > + * devices features are finalized. This is the default implementation.
> > + * Architecture implementations can override this.
> > + */
> > +
> > +int __weak arch_needs_virtio_iommu_platform(struct virtio_device *dev)
> > +{
> > +	return 0;
> > +}
> > +
> >   int virtio_finalize_features(struct virtio_device *dev)
> >   {
> >   	int ret = dev->config->finalize_features(dev);
> > @@ -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?

Yes, you are right,

Thanks,

Pierre

--
Pierre Morel
IBM Lab Boeblingen