On 2020-06-15 12:37, Halil Pasic wrote:

On Mon, 15 Jun 2020 11:01:55 +0800
Jason Wang [off-list ref] wrote:

quoted

quoted

hum, in between I found another way which seems to me much better:

We already have the force_dma_unencrypted() function available which
AFAIU is what we want for encrypted memory protection and is already
used by power and x86 SEV/SME in a way that seems AFAIU compatible
with our problem.

Even DMA and IOMMU are different things, I think they should be used
together in our case.

What do you think?

The patch would then be something like:

diff --git a/drivers/virtio/virtio.c b/drivers/virtio/virtio.c
index a977e32a88f2..53476d5bbe35 100644
--- a/drivers/virtio/virtio.c
+++ b/drivers/virtio/virtio.c

@@ -4,6 +4,7 @@
  #include <linux/virtio_config.h>
  #include <linux/module.h>
  #include <linux/idr.h>
+#include <linux/dma-direct.h>
  #include <uapi/linux/virtio_ids.h>

  /* Unique numbering for virtio devices. */

@@ -179,6 +180,10 @@ int virtio_finalize_features(struct virtio_device

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

+       if (force_dma_unencrypted(&dev->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)) {

I think this can work but need to listen from Michael

I don't think Christoph Hellwig will like force_dma_unencrypted()
in virtio code:
https://lkml.org/lkml/2020/2/20/630

Regards,
Halil

OK, then back to the first idea.
Thanks,

Pierre

-- 
Pierre Morel
IBM Lab Boeblingen