Date: Thu, 4 Jan 2018 21:39:24 +0100 (CET)
From: Jiri Kosina <jikos@kernel.org>
To: Alan Cox <gnomes@lxorguk.ukuu.org.uk>
cc: Pavel Machek <pavel@ucw.cz>,
        Linus Torvalds <torvalds@linux-foundation.org>,
        Dan Williams <dan.j.williams@intel.com>,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
        Mark Rutland <mark.rutland@arm.com>,
        linux-arch@vger.kernel.org, Peter Zijlstra <peterz@infradead.org>,
        Greg KH <gregkh@linuxfoundation.org>,
        Thomas Gleixner <tglx@linutronix.de>,
        Elena Reshetova <elena.reshetova@intel.com>
Subject: Re: [RFC PATCH] asm/generic: introduce if_nospec and
 nospec_barrier
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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