linux-kernel - Re: [RFC 09/10] x86/enter: Create macros to restrict/unrestrict Indirect Branch Speculation

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Date:   Tue, 23 Jan 2018 15:22:35 -0800
From:   Andi Kleen <ak@...ux.intel.com>
To:     "Woodhouse, David" <dwmw@...zon.co.uk>
Cc:     "thomas.lendacky@....com" <thomas.lendacky@....com>,
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Subject: Re: [RFC 09/10] x86/enter: Create macros to restrict/unrestrict
 Indirect Branch Speculation

On Tue, Jan 23, 2018 at 11:14:36PM +0000, Woodhouse, David wrote:
> On Tue, 2018-01-23 at 14:49 -0800, Andi Kleen wrote:
> > > Not sure.  Maybe to start, the answer might be to allow it to be set for
> > > the ultra-paranoid, but in general don't enable it by default.  Having it
> > > enabled would be an alternative to someone deciding to disable SMT, since
> > > that would have even more of a performance impact.
> > 
> > I agree. A reasonable strategy would be to only enable it for
> > processes that have dumpable disabled. This should be already set for
> > high value processes like GPG, and allows others to opt-in if
> > they need to.
> 
> That seems to make sense, and I think was the solution we were
> approaching for IBPB on context switch too, right?

Right.

-Andi