On 2020-06-29 17:57, Michael S. Tsirkin 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(+)

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?

Yes, you are right,

Thanks,

Pierre

-- 
Pierre Morel
IBM Lab Boeblingen