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

[David Woodhouse]

On Wed, 2018-01-10 at 16:13 +0100, Andrea Arcangeli wrote:
> 
> Can you also tell if IBRS must be written as a barrier to SPEC_CTRL in
> return to userland (kernel exit) when ibrs_enabled 2? Generally we
> wouldn't run a barrier there with ibrs_enabled 2, but absolutely
> nothing is intuitive here so I need to ask explicitly.

Since it achieves nothing but to make userspace run slower, there's no
need toÂwrite it again on returning to userspace. It will perform that
function just fine without doing so.


(Â that STIBP doesn't already do, and cheaper)

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