On Mon, 6 Jul 2020 15:37:37 +0200
Pierre Morel [off-list ref] wrote:

On 2020-07-02 15:03, Pierre Morel wrote:

quoted

On 2020-06-29 18:05, Cornelia Huck wrote:  

quoted

On Mon, 29 Jun 2020 11:57:14 -0400
"Michael S. Tsirkin" [off-list ref] wrote:
 

quoted

On Wed, Jun 17, 2020 at 12:43:57PM +0200, Pierre Morel wrote:  

quoted

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 <redacted>
Acked-by: Jason Wang <jasowang@redhat.com>
Acked-by: Christian Borntraeger <redacted>
---
  arch/s390/mm/init.c     |  6 ++++++
  drivers/virtio/virtio.c | 22 ++++++++++++++++++++++
  include/linux/virtio.h  |  2 ++
  3 files changed, 30 insertions(+)  

quoted

quoted

@@ -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?  

But it's only available with VERSION_1 anyway, isn't it? So it probably
also needs to fail when this feature is needed if VERSION_1 has not been
negotiated, I think.  

would be something like:

-       if (!virtio_has_feature(dev, VIRTIO_F_VERSION_1))
-               return 0;
+       if (!virtio_has_feature(dev, VIRTIO_F_VERSION_1)) {
+               ret = arch_accept_virtio_features(dev);
+               if (ret)
+                       dev_warn(&dev->dev,
+                                "virtio: device must provide 
VIRTIO_F_VERSION_1\n");
+               return ret;
+       }

That looks wrong; I think we want to validate in all cases. What about:

ret = arch_accept_virtio_features(dev); // this can include checking for
                                        // older or newer features
if (ret)
	// assume that the arch callback moaned already
	return ret;

if (!virtio_has_feature(dev, VIRTIO_F_VERSION_1))
	return 0;

// do the virtio-1 only FEATURES_OK dance

just a thought on the function name:
It becomes more general than just IOMMU_PLATFORM related.

What do you think of:

arch_accept_virtio_features()

Or maybe arch_validate_virtio_features()?

?

Regards,
Pierre