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

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

@@ -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.