On 06/27, Kees Cook wrote:

It looks like SMP ARM issues dsb for rmb, which seems a bit expensive.
http://infocenter.arm.com/help/index.jsp?topic=/com.arm.doc.dui0204g/CIHJFGFE.htm

...

I really want to avoid adding anything to the secure_computing()
execution path. :(

I must have missed something but I do not understand your concerns.

__secure_computing() is not trivial, and we are going to execute the
filters. Do you really think rmb() can add the noticeable difference?

Not to mention that we can only get here if we take the slow syscall
enter path due to TIF_SECCOMP...

Oleg.