linux-kernel - Re: [Patch v5 11/16] x86/speculation: Add Spectre v2 app to app protection modes

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Date:   Tue, 20 Nov 2018 00:01:34 +0100 (CET)
From:   Thomas Gleixner <tglx@...utronix.de>
To:     Tim Chen <tim.c.chen@...ux.intel.com>
cc:     Jiri Kosina <jikos@...nel.org>,
        Tom Lendacky <thomas.lendacky@....com>,
        Ingo Molnar <mingo@...hat.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Josh Poimboeuf <jpoimboe@...hat.com>,
        Andrea Arcangeli <aarcange@...hat.com>,
        David Woodhouse <dwmw@...zon.co.uk>,
        Andi Kleen <ak@...ux.intel.com>,
        Dave Hansen <dave.hansen@...el.com>,
        Casey Schaufler <casey.schaufler@...el.com>,
        Asit Mallick <asit.k.mallick@...el.com>,
        Arjan van de Ven <arjan@...ux.intel.com>,
        Jon Masters <jcm@...hat.com>,
        Waiman Long <longman9394@...il.com>,
        linux-kernel@...r.kernel.org, x86@...nel.org
Subject: Re: [Patch v5 11/16] x86/speculation: Add Spectre v2 app to app
 protection modes

On Mon, 19 Nov 2018, Tim Chen wrote:
> On 11/19/2018 12:55 PM, Jiri Kosina wrote:
> > On Mon, 19 Nov 2018, Thomas Gleixner wrote:
> > 
> >>
> >> So before that change IBPB was usable without STIBP, now not longer. What's
> >> the rationale?
> >>
> >> This patch changes a gazillion things at once and is completely
> >> unreviewable.
> > 
> > The patchset actually ties together IBPB and STIBP pretty closely, which 
> > is IMO a good thing; there is no good reason why anone would want just one 
> > of those (or each in a different mode), at least before this magical 
> > coscheduling exists.
> > 
> > But I guess this fact should be documented somewhere.
> > 
> 
> Yes, it wouldn't make sense for having just one of those if a task
> is worried about attack from user space.
> 
> I'll document it.

What? IBPB makes tons of sense even without STIBP.

Thanks,

	tglx