Re: [ofa-general] Re: [patch 0/6] MMU Notifiers V6

Roland Dreier
2008-02-09T00:13:00Z

> We have done several rounds of discussion on linux-kernel about this so
> far and the IB folks have not shown up to join in. I have tried to make
> this as general as possible.

Sorry, this has been on my "things to look at" list for a while, but I
haven't gotten a chance to really understand where things are yet.

In general, this MMU notifier stuff will only be useful to a subset of
InfiniBand/RDMA hardware. Some adapters are smart enough to handle
changing the IO virtual -> bus/physical mapping on the fly, but some
aren't. For the dumb adapters, I think the current ib_umem_get() is
pretty close to as good as we can get: we have to keep the physical
pages pinned for as long as the adapter is allowed to DMA into the
memory region.

For the smart adapters, we just need a chance to change the adapter's
page table when the kernel/CPU's mapping changes, and naively, this
stuff looks like it would work.

Andrew, does that help?

- R.