Resuming with superpages broke VMI/altp2m workflow

[Petr Beneš <w1benny@xxxxxxxxx>]

Hi,
After updating to RELEASE-4.21.0 my VMI tool stopped working.

My VMI tool extensively uses altp2m and sets specific access rights to
various pages in the alt-views (e.g. X-only rights to achieve
"invisible breakpoints"). In RELEASE-4.21.0, I noticed that the
memory-access events were hitting for nonsensical pages.

After git bisecting, the offending commit appears to be 50baf2d
(tools/libs/guest: Use superpages where possible on migrate/resume).

I don't think the issue is really there - reverted VMs work always
fine. Instead, I suspect the issue will be in incorrectly splitting
altp2m superpages, since the issue always appears after manually
setting memory-access rights for altp2m pages.

Best,
Petr