When a copy function hits a bad page and the page is not yet known
be bad, what does it do? (I.e. the page was believed to be fine but
the copy function gets #MC.) Does it unmap it right away? What does
I suspect that we will only ever find a handful of situations where the
kernel can recover from memory that has gone bad that are worth fixing
(got to be some code path that touches a meaningful fraction of memory,
otherwise we get code complexity without any meaningful payoff).
I don't think we'd want different actions for the cases of "we just found
now that this page is bad" and "we got a notification an hour ago that this
page had gone bad". Currently we treat those the same for application
errors ... SIGBUS either way.
 well there are options both globally and at the per-process level to have
the "early" notifications delivered right away.