[PATCH 0/1] x86/speculation: Allow IBPB to be conditionally enabled on CPUs with always-on STIBP

From: Anand K Mistry
Date: Thu Oct 29 2020 - 03:42:47 EST


When attempting to do some performance testing of IBPB on and AMD
platform, I noticed the IBPB instruction was never being issued, even
though it was conditionally on and various seccomp protected processes
were force enabling it. Turns out, on those AMD CPUs, STIBP is set to
always-on and this was causing an early-out on the prctl() which turns
off IB speculation. Here is my attempt to fix it.

I'm hoping someone that understands this better than me can explain why
I'm wrong.


Anand K Mistry (1):
x86/speculation: Allow IBPB to be conditionally enabled on CPUs with
always-on STIBP

arch/x86/kernel/cpu/bugs.c | 41 +++++++++++++++++++++-----------------
1 file changed, 23 insertions(+), 18 deletions(-)

--
2.29.1.341.ge80a0c044ae-goog