On Thu, 2020-07-23 at 17:49 +0200, Peter Zijlstra wrote:

'What does noinstr mean? and why do we have it" -- don't dare touch
the
entry code until you can answer that.

noinstr disables instrumentation, so there would not be calls and
dependencies on other parts of the kernel when it's not yet safe to
call them. Relevant functions already have it, and I add an inline call
to perform flags update and synchronization. Unless something else is
involved, those operations are safe, so I am not adding anything that
can break those.

-- 
Alex