[Mpi3-rma] Fix for win_allocate_shared

[Torsten Hoefler]

Hi all,

So to fix the recently discovered problem in the separate model and
win_allocate_shared, the formed ad-hoc working group proposes the
following:

Add the following sentence to
https://svn.mpi-forum.org/trac/mpi-forum-web/raw-attachment/ticket/284/one-side-2.pdf
page 46 line 47 after ".. obey the following rules.":

"For shared memory windows (cf. Section~\ref{sec:alloc_shared}), a
store/load that accesses a memory region that is logically associated
with a remote process is equivalent to a put/get in the following
rules."

And add the following advice to implementors on page 47 line 33 after
"... made visible to the other).":

"The semantic rules for shared memory windows in the MPI_RMA_SEPARATE 
model allow concurrent load/store accesses from two distinct processes 
to the same target window that is remote to both processes. An
implementation cannot expose shared memory windows on hardware that does
not support this access mode."

I'm sure the wording can be tweaked (please propose changes here) but
this is what we came up with. Please comment!

We plan to discuss this later in the full forum because there are some
trade-offs involved here.

All the Best,
  Torsten

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Torsten Hoefler         | Performance Modeling and Simulation Lead
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