On Mon, Oct 09, 2017 at 01:18:20PM -0600, Jason Gunthorpe wrote:

quoted

quoted

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?

I don't think this has ever come up in the context of an all-device MR
invalidate requirement. Drivers already have code to invalidate
specifc MRs, but to find all MRs that touch certain pages and then
invalidate them would be new code.

The whole point is that we should not need that IFF we provide the
right interface.

If we have a new 'register memory with a lease', the driver (or in fact
probably the umem core for the drivers using it) has the lease associated
with the ib_umem structure, which will just need a backpointer from the
ib_umem to the to the MR to unregister it.

Which might be a good opportunity to break the user MR from the in-kernel
ones and merge it with ib_umem, but that's a different story..
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