Re: [RFC PATCH] asm/generic: introduce if_nospec and nospec_barrier

[Pavel Machek]

On Thu 2018-01-04 21:23:59, Alan Cox wrote:
> On Thu, 4 Jan 2018 21:39:24 +0100 (CET)
> Jiri Kosina <jikos@xxxxxxxxxx> wrote:
> 
> > On Thu, 4 Jan 2018, Alan Cox wrote:
> > 
> > > You never go from one user process to another except via the kernel. We
> > > have no hardware scheduling going on. That means that if the kernel
> > > and/or CPU imposes the correct speculation barriers you can't attack
> > > anyone but yourself.  
> > 
> > So how does this work on HT with the shared BTB? There is no context 
> > switch (and hence no IBPB) happening between the threads sharing it.
> > 
> 
> If you are paranoid in that case you either need to schedule things that
> trust each other together or disable the speculation while that situation
> occurs. However the kernel is always in the position to make that
> decision.

Actually... I'm not paranoid but would like to run flightgear on one
core (smt cpu #0), with smt cpu#1 being idle, while running
compilations on second core (smt cpus #2 and #3).

Is there easy way to do that?
									Pavel

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