You either have to pause the caller or prevent the caller from trampling the memory while the callee is using it. If you look at previous work like VMRPC (https://ieeexplore.ieee.org/document/5542746/) they make the shared area read-only while the callee is using it.

In IPRE, I am pausing the caller while the remote call is on-going, which means "just having a shared block" is inferior to just sharing everything. It's just so much easier and nicer to be able to pass literally anything you want.

The caveat is that the callee has to wait, but I think the fact that the remote is now running in the SAME THREAD without any scheduling involved makes up for it. It's a true synchronous remote function call with some overhead.