Hi Mike,
This commit is making my intel box not boot in mm-unstable :>) I bisected it to this commit.
For what it's worth, we've found the same under Xen too.
There's one concrete bug in the series, failing to cope with the absence of superpages (fix in https://lore.kernel.org/xen-devel/6bb03333-74ca-4c2c-85a8-72549b85a5b4@suse.... but not formally posted yet AFAICT).
The rest of the thread then found a crash looking to be the same as reported here, but you've made better progress narrowing it down than we have.
~Andrew