Messages in this thread | | | Date | Fri, 23 Nov 2018 00:28:42 +0100 (CET) | From | Jiri Kosina <> | Subject | Re: [patch 21/24] x86/speculation: Prepare arch_smt_update() for PRCTL mode |
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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.
True.
> 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 SUSE Labs
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