From mboxrd@z Thu Jan  1 00:00:00 1970
Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand
        id S1753676AbeAJAui (ORCPT <rfc822;ralf@linux-mips.org> + 1 other);
        Tue, 9 Jan 2018 19:50:38 -0500
Received: from Galois.linutronix.de ([146.0.238.70]:53853 "EHLO
        Galois.linutronix.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org
        with ESMTP id S1751329AbeAJAuh (ORCPT
        <rfc822;linux-kernel@vger.kernel.org>);
        Tue, 9 Jan 2018 19:50:37 -0500
Date: Wed, 10 Jan 2018 01:50:30 +0100 (CET)
From: Thomas Gleixner <tglx@linutronix.de>
To: Tom Lendacky <thomas.lendacky@amd.com>
cc: Linus Torvalds <torvalds@linux-foundation.org>,
        Andi Kleen <andi@firstfloor.org>,
        the arch/x86 maintainers <x86@kernel.org>,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
        David Woodhouse <dwmw@amazon.co.uk>,
        Paul Turner <pjt@google.com>,
        Andrew Lutomirski <luto@kernel.org>,
        Peter Zijlstra <peterz@infradead.org>,
        Tim Chen <tim.c.chen@linux.intel.com>,
        Greg Kroah-Hartman <gregkh@linux-foundation.org>,
        Dave Hansen <dave.hansen@intel.com>,
        Jiri Kosina <jikos@kernel.org>, Andi Kleen <ak@linux.intel.com>
Subject: Re: [PATCH] x86/retpoline: Fix NOSPEC_JMP for tip
In-Reply-To: <184a65a3-6afe-4c82-7f7d-2c1d4a5198bc@amd.com>
Message-ID: <alpine.DEB.2.20.1801100150010.2200@nanos>
References: <20180110003139.10531-1-andi@firstfloor.org> <CA+55aFzyVFEUKaLpqxfwh5E9QFgMjzr+wVoYGxqTHVDkGcFkOw@mail.gmail.com> <alpine.DEB.2.20.1801100139560.2200@nanos> <184a65a3-6afe-4c82-7f7d-2c1d4a5198bc@amd.com>
User-Agent: Alpine 2.20 (DEB 67 2015-01-07)
MIME-Version: 1.0
Content-Type: text/plain; charset=US-ASCII
X-Linutronix-Spam-Score: -1.0
X-Linutronix-Spam-Level: -
X-Linutronix-Spam-Status: No , -1.0 points, 5.0 required,  ALL_TRUSTED=-1,SHORTCIRCUIT=-0.0001
Sender: linux-kernel-owner@vger.kernel.org
List-ID: <linux-kernel.vger.kernel.org>
X-Mailing-List: linux-kernel@vger.kernel.org
Return-Path: <linux-kernel-owner@vger.kernel.org>

On Tue, 9 Jan 2018, Tom Lendacky wrote:
> On 1/9/2018 6:40 PM, Thomas Gleixner wrote:
> > On Tue, 9 Jan 2018, Linus Torvalds wrote:
> > 
> >> On Tue, Jan 9, 2018 at 4:31 PM, Andi Kleen <andi@firstfloor.org> wrote:
> >>>
> >>> The following patch fixes it for me. Something doesn't
> >>> seem to work with ALTERNATIVE_2. It adds only a few bytes
> >>> more code, so seems acceptable.
> >>
> >> Ugh. It's kind of stupid, though.
> >>
> >> Why is the code sequence not simply:
> >>
> >>   ALTERNATIVE "", "lfence", X86_FEATURE_RETPOLINE_AMD
> >>   ALTERNATIVE __stringify(jmp *\reg), __stringify(RETPOLINE_JMP \reg),
> >> X86_FEATURE_RETPOLINE
> >>
> >> ie make that X86_FEATURE_RETPOLINE_AMD _only_ emit the "lfence", and
> >> simply fall through to what will be the "jmp *\reg" of the
> >> non-RETPOLINE version.
> >>
> >> Then just make sure X86_FEATURE_RETPOLINE_AMD disables X86_FEATURE_RETPOLINE.
> 
> I think there are areas that rely on X86_FEATURE_RETPOLINE being set
> even if X86_FEATURE_RETPOLINE_AMD is set.  For example, line 261 in
> arch/x86/entry/entry_32.S is only checking for X86_FEATURE_RETPOLINE.

That should be fixable

Thanks,

	tglx