Yep. However, so far, it requires an application to explicitly opt in
to this behavior, so it's not all that bad. Your patch would remove
the requirement for application opt-in, which, in my opinion, makes
this way worse and reduces the number of applications for which this
is acceptable.
As far as I know, basically nobody is using KSM at this point. There
are blog posts from several cloud providers about these security risks
that explicitly state that they're not using memory deduplication.