From: Khalid Aziz <redacted>
Date: Mon, 7 Mar 2016 14:27:09 -0700

I agree with your point of view. PSTATE.mcde and TTE.mcd are set in
response to request from userspace. If userspace asked for them to be
set, they already know but it was the database guys that asked for
these two functions and they are the primary customers for the ADI
feature. I am not crazy about this idea since this extends the
mprotect API even further but would you consider using the return
value from mprotect to indicate if PSTATE.mcde or TTE.mcd were already
set on the given address?

Well, that's the idea.

If the mprotect using MAP_ADI or whatever succeeds, then ADI is
enabled.

Users can thus also pass MAP_ADI as a flag to mmap() to get ADI
protection from the very beginning.