Re: [patch RFC 5/5] x86/speculation: Add basic speculation control code

[Jiri Kosina]

On Wed, 10 Jan 2018, Andrea Arcangeli wrote:

> Perhaps the confusing come from "less privileged prediction mode" and
> you thought that meant "less privileged ring mode". It says "predction
> mode" not ring 3.

Well, prediction mode is defined by "CPL3 vs CPL0-2" and "VMX root vs VMX 
non-root", with obvious ordering of privileges.

So if IBRS is set, branch predictor will not allow the predicted target to 
be influenced by code that executed in less privileged prediction mode 
before value of '1' IBRS mode was last written to, and that's pretty much 
it.

-- 
Jiri Kosina
SUSE Labs