[openib-general] FMR and how they work

[Sean Hefty]

Fab Tillier wrote:

> When you deregister a FMR, what information from that FMR can the HCA cache
> - just the MTTs or also the MPTs?  Can an incoming RDMA transfer access the
> pages previously referenced by that FMR?  If so, for how long?  When is it
> safe to unpin the pages?
> 
> What about when you modify the FMR?  How long are previous mappings "at
> risk" of transfers?
> 
> I'm kinda confused because the Mellanox docs indicate that the HCA can cache
> stuff and that the pages can't be unpinned until the cache is flushed.  If
> that's true, I don't see how FMRs can be used because they could be suspect
> to malicious use by a remote host.

Based on my understanding of Mellanox FMRs, I thought that this true. 
The buffers are still available to the remote host even after 
deregistration occurs.  Of course my understanding could be wrong...

- Sean