On Sat, 5 Jan 2019, Linus Torvalds wrote:

quoted

There are possibilities [1] how mincore() could be used as a converyor of
a sidechannel information about pagecache metadata.

Can we please just limit it to vma's that are either anonymous, or map
a file that the user actually owns?

Then the capability check could be for "override the file owner check"
instead, which makes tons of sense.

Makes sense. 

I am still not completely sure what to return in such cases though; we can 
either blatantly lie and always pretend that the pages are resident (to 
avoid calling process entering some prefaulting mode), or return -ENOMEM 
for mappings of files that don't belong to the user (in case it's not 
CAP_SYS_ADMIN one).

-- 
Jiri Kosina
SUSE Labs