Re: [PATCH v2 1/1] s390: virtio: let arch accept devices without IOMMU feature

[Pierre Morel <pmorel@xxxxxxxxxxxxx>]

On 2020-06-16 08:55, Christian Borntraeger wrote:
> On 15.06.20 14:39, 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: Christian Borntraeger <borntraeger@xxxxxxxxxx>

Thanks,

> Shouldnt we maybe add a pr_warn if that happens to help the admins to understand what is going on?

Yes, Connie asked for it too, good that you remind it to me, I add it.

Thanks,
Pierre

> > ---
> >   arch/s390/mm/init.c     | 6 ++++++
> >   drivers/virtio/virtio.c | 9 +++++++++
> >   include/linux/virtio.h  | 2 ++
> >   3 files changed, 17 insertions(+)
> >
> > diff --git a/arch/s390/mm/init.c b/arch/s390/mm/init.c
> > index 87b2d024e75a..3f04ad09650f 100644
> > --- a/arch/s390/mm/init.c
> > +++ b/arch/s390/mm/init.c
> > @@ -46,6 +46,7 @@
> >   #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);
> >   
> > @@ -162,6 +163,11 @@ bool force_dma_unencrypted(struct device *dev)
> >   	return is_prot_virt_guest();
> >   }
> >   
> > +int arch_needs_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..30091089bee8 100644
> > --- a/drivers/virtio/virtio.c
> > +++ b/drivers/virtio/virtio.c
> > @@ -167,6 +167,11 @@ void virtio_add_status(struct virtio_device *dev, unsigned int status)
> >   }
> >   EXPORT_SYMBOL_GPL(virtio_add_status);
> >   
> > +int __weak arch_needs_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 +184,10 @@ int virtio_finalize_features(struct virtio_device *dev)
> >   	if (!virtio_has_feature(dev, VIRTIO_F_VERSION_1))
> >   		return 0;
> >   
> > +	if (arch_needs_iommu_platform(dev) &&
> > +		!virtio_has_feature(dev, VIRTIO_F_IOMMU_PLATFORM))
> > +		return -EIO;
> > +
> >   	virtio_add_status(dev, VIRTIO_CONFIG_S_FEATURES_OK);
> >   	status = dev->config->get_status(dev);
> >   	if (!(status & VIRTIO_CONFIG_S_FEATURES_OK)) {
> > diff --git a/include/linux/virtio.h b/include/linux/virtio.h
> > index a493eac08393..2c46b310c38c 100644
> > --- a/include/linux/virtio.h
> > +++ b/include/linux/virtio.h
> > @@ -195,4 +195,6 @@ void unregister_virtio_driver(struct virtio_driver *drv);
> >   #define module_virtio_driver(__virtio_driver) \
> >   	module_driver(__virtio_driver, register_virtio_driver, \
> >   			unregister_virtio_driver)
> > +
> > +int arch_needs_iommu_platform(struct virtio_device *dev);
> >   #endif /* _LINUX_VIRTIO_H */

--
Pierre Morel
IBM Lab Boeblingen