On Mon, Oct 9, 2017 at 11:58 AM, Jason Gunthorpe
[off-list ref] wrote:

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

quoted

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..

Sounds promising. All I want in the end is to be sure that the kernel
is enabled to stop any in-flight RDMA at will without asking
userspace. Does this require per-RDMA driver opt-in or is there a
common call that can be made?

Outside of that the re-use problem is already solved by just unmapping
(iommu_unmap()) the IOVA, but keeping it allocated until the eventual
dma_unmap_sg() at memory un-registration time frees it.

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