linux-kernel - Re: [patch 05/24] x86/speculation: Disable STIBP when enhanced IBRS is in use

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Message-ID: <alpine.DEB.2.21.1811212300340.1665@nanos.tec.linutronix.de>
Date:   Wed, 21 Nov 2018 23:01:03 +0100 (CET)
From:   Thomas Gleixner <tglx@...utronix.de>
To:     Borislav Petkov <bp@...en8.de>
cc:     LKML <linux-kernel@...r.kernel.org>, x86@...nel.org,
        Peter Zijlstra <peterz@...radead.org>,
        Andy Lutomirski <luto@...nel.org>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Jiri Kosina <jkosina@...e.cz>,
        Tom Lendacky <thomas.lendacky@....com>,
        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>,
        Greg KH <gregkh@...uxfoundation.org>,
        Dave Stewart <david.c.stewart@...el.com>,
        Kees Cook <keescook@...omium.org>,
        Tim Chen <tim.c.chen@...ux.intel.com>
Subject: Re: [patch 05/24] x86/speculation: Disable STIBP when enhanced IBRS
 is in use

On Wed, 21 Nov 2018, Thomas Gleixner wrote:
> On Wed, 21 Nov 2018, Borislav Petkov wrote:
> > >  static char *stibp_state(void)
> > >  {
> > > +	if (spectre_v2_enabled == SPECTRE_V2_IBRS_ENHANCED)
> > > +		return "";
> > 
> > If
> > 	spectre_v2_enabled == SPECTRE_V2_IBRS_ENHANCED
> > 
> > then SPEC_CTRL_STIBP should not be set in x86_spec_ctrl_base
> > (stibp_needed() prevents the setting in arch_smt_update()) so the above
> > check should not be needed.
> > 
> > I *think*.
> 
> Yes, makes sense.

For this patch, but for the final thing it does not.

Thanks,

	tglx