quoted

Maybe the other difference in approach between Andy and me is whether to
go for a solution that covers all the corner cases, or just make an incremental
improvement that allows for recover in some useful subset of remaining fatal
cases, but still dies in other cases.

Does that mean more core code surgery?

Yes. I need to look at other user access inside pagefault_disable/enable()
as likely spots where the code may continue after a machine check and
retry the access.  So expect some more "if (ret == ENXIO) { do something to give up gracefully }"

quoted

I'm happy to replace error messages with ones that are more descriptive and
helpful to humans.

Yap, that: "Multiple copyin" with something more understandable to users...

I'll work on it. We tend not to have essay length messages as panic() strings. But I can
add a comment in the code there so that people who grep whatever panic message
we choose can get more details on what happened and what to do.

-Tony