Comment 7 for bug 1646805

The commit posted in comment #6 has been in mainline since 4.16-rc5, so it is already in Cosmic, Disco and the test kernel I posted. The commit is:
61e18270f604 ("s390: Fix runtime warning about negative pgtables_bytes")

So maybe there are other commit(s) needed to fix those messages. Did the test kernel fix the original issue? If so, maybe I can build a linux-next kernel for you to see if a fix for the console messages is available.