linux-kernel - Re: [RFC PATCH] asm/generic: introduce if_nospec and nospec

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Message-ID: <20180104214809.GB18699@amd>
Date:   Thu, 4 Jan 2018 22:48:09 +0100
From:   Pavel Machek <pavel@....cz>
To:     Alan Cox <gnomes@...rguk.ukuu.org.uk>
Cc:     Jiri Kosina <jikos@...nel.org>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Dan Williams <dan.j.williams@...el.com>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Mark Rutland <mark.rutland@....com>,
        linux-arch@...r.kernel.org, Peter Zijlstra <peterz@...radead.org>,
        Greg KH <gregkh@...uxfoundation.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Elena Reshetova <elena.reshetova@...el.com>
Subject: Re: [RFC PATCH] asm/generic: introduce if_nospec and nospec_barrier

On Thu 2018-01-04 21:23:59, Alan Cox wrote:
> On Thu, 4 Jan 2018 21:39:24 +0100 (CET)
> Jiri Kosina <jikos@...nel.org> 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

-- 
(english) http://www.livejournal.com/~pavelmachek
(cesky, pictures) http://atrey.karlin.mff.cuni.cz/~pavel/picture/horses/blog.html

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