Re: Problem with RDMA device removal architecture

[Steve Wise <swise-7bPotxP6k4+P2YhJcF5u+vpXobYPEAuW@public.gmane.org>]

Roland Dreier wrote:
>  > In other words, I think we want the ucma context to stay around until
>  > the application destroys it (via explicit means or via exit).   But
>  > the rdma_cm_id gets destroyed immediately upon receiving a
>  > DEVICE_REMOVE event.
>
> Yes.  The RDMA CM is somewhat easier, but I think the basic idea should
> be that ucma internally detaches the userspace context from anything
> that is holding a device reference, and marks the context as "dead"
> (only valid operation is destroying it).
>
> uverbs is trickier, because a userspace process will typically have some
> hardware resources directly mmap'ed.  We need a way to "revoke" that
> mmap and have it point at a dummy page until userspace releases it --
> and last I looked I wasn't sure how to do that.
>   
hmm.  Yes, now I remember our last discussion and why we punted? :) 

Also, this is a device-specific issue.  Each rdma device driver/provider 
would have to deal with this.  But like you said, if the driver can 
revoke and remap to a dummy page, then we could avoid inadvertent 
process crashes...

Anyone out there know how we can do this? 


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