[openib-general] [RFC/BUG] libibverbs: DMA vs. CQ race

[glebn at voltaire.com]

On Wed, Dec 13, 2006 at 11:41:41PM -0800, Roland Dreier wrote:
> Are there other possible ordering problems involving user memory (not
> in a CQ or QP)?  Something like a CPU on node A writing to memory on
> node B and then posting a work request that makes the HCA DMA from
> that memory on node B, and having the work request doorbell reach the
> HCA before the write to node B actually happens, so the HCA DMAs the
> old contents of node B's memory?
> 
> I guess the only feasible solution to the problem you're pointing out
> is to have libmthca use some special mmap()-based allocator for queues
> so that the kernel can give it memory that has the special
> dma_map_consistent treatment.
Do you think this should be part of mthca or some general framework like uio
which allows writing driver in userspace?
Also another solution could be to do something similar to ehca. It
allocates QP and CQ in the kernel and maps them into process address
space.

--
			Gleb.