Re: [PATCH v5 2/2] s390: virtio: PV needs VIRTIO I/O device protection

[Pierre Morel]

On 2020-07-09 10:57, Cornelia Huck wrote:
> On Thu,  9 Jul 2020 10:39:19 +0200
> Pierre Morel <pmorel@xxxxxxxxxxxxx> wrote:
>
> > If protected virtualization is active on s390, the virtio queues are
> > not accessible to the host, unless VIRTIO_F_IOMMU_PLATFORM has been
> > negotiated. Use the new arch_validate_virtio_features() interface to
> > fail probe if that's not the case, preventing a host error on access
> > attempt
> >
> > Signed-off-by: Pierre Morel <pmorel@xxxxxxxxxxxxx>
> > ---
> >   arch/s390/mm/init.c | 27 +++++++++++++++++++++++++++
> >   1 file changed, 27 insertions(+)
> >
> > diff --git a/arch/s390/mm/init.c b/arch/s390/mm/init.c
> > index 6dc7c3b60ef6..b8e6f90117da 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_config.h>
> >   
> >   pgd_t swapper_pg_dir[PTRS_PER_PGD] __section(.bss..swapper_pg_dir);
> >   
> > @@ -161,6 +162,32 @@ bool force_dma_unencrypted(struct device *dev)
> >   	return is_prot_virt_guest();
> >   }
> >   
> > +/*
> > + * arch_validate_virtio_features
> > + * @dev: the VIRTIO device being added
> > + *
> > + * Return an error if required features are missing on a guest running
> > + * with protected virtualization.
> > + */
> > +int arch_validate_virtio_features(struct virtio_device *dev)
> > +{
> > +	if (!is_prot_virt_guest())
> > +		return 0;
> > +
> > +	if (!virtio_has_feature(dev, VIRTIO_F_VERSION_1)) {
> > +		dev_warn(&dev->dev, "device must provide VIRTIO_F_VERSION_1\n");
>
> I'd probably use "legacy virtio not supported with protected
> virtualization".
>
> > +		return -ENODEV;
> > +	}
> > +
> > +	if (!virtio_has_feature(dev, VIRTIO_F_IOMMU_PLATFORM)) {
> > +		dev_warn(&dev->dev,
> > +			 "device must provide VIRTIO_F_IOMMU_PLATFORM\n");
>
> "support for limited memory access required for protected
> virtualization"
>
> ?
>
> Mentioning the feature flag is shorter in both cases, though.

And I think easier to look for in case of debugging purpose.
I change it if there is more demands.

> > +		return -ENODEV;
> > +	}
> > +
> > +	return 0;
> > +}
> > +
> >   /* protected virtualization */
> >   static void pv_init(void)
> >   {
>
> Either way,
>
> Reviewed-by: Cornelia Huck <cohuck@xxxxxxxxxx>

Thanks,
Pierre


--
Pierre Morel
IBM Lab Boeblingen