Comment 3 for bug 1868628

Also, this patch:
 - mm: make page ref count overflow check tighter and more explicit

seems to exist already in the xenial tree:

"d4a5d4fe58f1c28 mm: make page ref count overflow check tighter and more explicit"

which was part of the fix for CVE-2019-11487

Both the xenial patch and the linux-stable patch purport to backport f958d7b528b1b40c44cfda5eabe2d82760d868c3 - however, they are different from each other. The one that we already had in Xenial is the one that looks like the upstream patch. The linux-stable version of the patch is quite different.

I will check with Cascardo on what to do about this.