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

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Message-ID: <nycvar.YFH.7.76.1801042137560.11852@cbobk.fhfr.pm>
Date:   Thu, 4 Jan 2018 21:39:24 +0100 (CET)
From:   Jiri Kosina <jikos@...nel.org>
To:     Alan Cox <gnomes@...rguk.ukuu.org.uk>
cc:     Pavel Machek <pavel@....cz>,
        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, 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.

-- 
Jiri Kosina
SUSE Labs