On Thu, 2018-04-05 at 21:34 +0300, Michael S. Tsirkin wrote:

quoted

In this specific case, because that would make qemu expect an iommu,
and there isn't one.

I think that you can set iommu_platform in qemu without an iommu.

No I mean the platform has one but it's not desirable for it to be used
due to the performance hit.

Cheers,
Ben.

quoted

Anshuman, you need to provide more background here. I don't have time
right now it's late, but explain about the fact that this is for a
specific type of secure VM which has only a limited pool of (insecure)
memory that can be shared with qemu, so all IOs need to bounce via that
pool, which can be achieved by using swiotlb.

Note: this isn't urgent, we can discuss alternative approaches, this is
just to start the conversation.

Cheers,
Ben.