[lkml]   [2018]   [Nov]   [23]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
Messages in this thread
SubjectRe: [patch 21/24] x86/speculation: Prepare arch_smt_update() for PRCTL mode
On Fri, 23 Nov 2018, Thomas Gleixner wrote:

> > So I'm wondering, shouldn't firmware_restrict_branch_speculation_start()/_end()
> > also enable/disable STIBP? It already enabled/disables IBRS.
> IBRS includes STIBP.


> We don't use IBRS in the kernel otherwise because you'd have to do more
> MSR writes on the protection boundaries.

Just for the record -- we do have an option for IBRS in our distro kernel
on SKL+ systems.

There definitely is a measurable performance impact, but the MSR writes on
protection boundaries are totally cheap compared to the actual IBRS
runtime operation effect.

Jiri Kosina

 \ /
  Last update: 2018-11-23 00:29    [W:0.072 / U:0.568 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site