On Fri, Jul 6, 2018 at 12:38 PM Mathieu Desnoyers
<mathieu.desnoy...@efficios.com> wrote:
>
> Should I change all 4 bytes __get_user()/__put_user() in kernel/rseq.c
> for get_user()/put_user() to ensure consistency ?
Probably.
*If* this actually turns out to be somethinig that shows up on
profiles, it's almost certainly going to be the STAC/CLAC instructions
("perf report" tends to report them as three one-byte nop's because
that's how they look before instruction replacement).
And then it's not __get/put_user() that will improve things, but doing a
user_access_begin();
.. do unsafe_get/put_user() ..
user_access_end();
that will improve performance.
But it is *very* seldom useful. We have it in a handful of places in
the kernel, and the most noticeable one is
lib/{strnlen,strncpy_from}_user.c
Linus
