Re: [PATCH v7 07/12] dma-mapping: introduce dma_has_iommu()

On Fri, Oct 06, 2017 at 03:35:54PM -0700, Dan Williams wrote:

otherwise be quiesced. The need for this knowledge is driven by a need
to make RDMA transfers to DAX mappings safe. If the DAX file's block map
changes we need to be to reliably stop accesses to blocks that have been
freed or re-assigned to a new file.

If RDMA is driving this need, why not invalidate backing RDMA MRs
instead of requiring a IOMMU to do it? RDMA MR are finer grained and
do not suffer from the re-use problem David W. brought up with IOVAs..

Jason