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

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Message-ID: <alpine.DEB.2.21.1811200100440.1669@nanos.tec.linutronix.de>
Date:   Tue, 20 Nov 2018 01:02:20 +0100 (CET)
From:   Thomas Gleixner <tglx@...utronix.de>
To:     Jiri Kosina <jikos@...nel.org>
cc:     Dave Hansen <dave.hansen@...el.com>,
        Tim Chen <tim.c.chen@...ux.intel.com>,
        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>,
        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 Tue, 20 Nov 2018, Jiri Kosina wrote:
> On Mon, 19 Nov 2018, Dave Hansen wrote:
> 
> > > What? IBPB makes tons of sense even without STIBP.
> > 
> > I'm lost. :)
> > 
> > I don't think anyone is talking about using STIBP *everywhere* that IBPB
> > is in-use.
> > 
> > We're just guessing that, if anybody is paranoid enough to ask for IBPB,
> > *and* they have SMT, they almost certainly want STIBP too.
> 
> I think you are not lost :) and this is exactly what makes sense, and what 
> Tim's patchset implements.

Tries to implement perhaps. Unless IBPB is never available when STIBP is
not available, but according to documentation that's unlikely because STIBP
can be unset when the CPU does not support HT at all.

Thanks,

	tglx