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

[Pierre Morel]

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 <pmo...@linux.ibm.com>

Acked-by: Christian Borntraeger <borntrae...@de.ibm.com>

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