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

Michael S. Tsirkin
2020-06-29T18:58:21Z

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@linux.ibm.com>
> Acked-by: Jason Wang <jasowang@redhat.com>
> Acked-by: Christian Borntraeger <borntraeger@de.ibm.com>
> ---
> 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?

> diff --git a/include/linux/virtio.h b/include/linux/virtio.h
> index a493eac08393..e8526ae3463e 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_virtio_iommu_platform(struct virtio_device *dev);
> #endif /* _LINUX_VIRTIO_H */
> --
> 2.25.1