On Thu, Mar 21, 2013 at 12:15:33AM -0700, Roland Dreier wrote: > >> I think this change will break the case where userspace tries to > >> register an MR with read-only permission, but intends locally through > >> the CPU to write to the memory. > > > Shouldn't it set LOCAL_WRITE then? > > We're talking about the permissions for the register MR operation, > right? (That's what the kernel RDMA driver code that does > get_user_pages() sees) > > In that case, no, I don't see any reason for LOCAL_WRITE, since the > only RDMA operations that will access this memory are remote reads.
What is the meaning of LOCAL_WRITE then? There are no local RDMA writes as far as I can see. > The writing (that triggers COW) is coming from normal process access > triggering a page fault, etc. This is a pretty standard way of using > RDMA... For example, I allocate some memory and register it for RDMA > read (and pass the R_Key to the remote system) with only REMOTE_READ > permission. Then I fill in the memory with the results of some > computation and the remote system does an RDMA read to get those > results. > > - R. OK then what we need is a new flag saying "I really do not intend to write into this memory please do not break COW or do anything else just in case I do". -- MST -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
