From mboxrd@z Thu Jan  1 00:00:00 1970
Return-Path: <SRS0=Hds+=OG=vger.kernel.org=linux-kernel-owner@kernel.org>
X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on
	aws-us-west-2-korg-lkml-1.web.codeaurora.org
X-Spam-Level: 
X-Spam-Status: No, score=-1.0 required=3.0 tests=MAILING_LIST_MULTI,SPF_PASS
	autolearn=ham autolearn_force=no version=3.4.0
Received: from mail.kernel.org (mail.kernel.org [198.145.29.99])
	by smtp.lore.kernel.org (Postfix) with ESMTP id 126BCC43441
	for <linux-kernel@archiver.kernel.org>; Tue, 27 Nov 2018 07:30:13 +0000 (UTC)
Received: from vger.kernel.org (vger.kernel.org [209.132.180.67])
	by mail.kernel.org (Postfix) with ESMTP id CAA1B21104
	for <linux-kernel@archiver.kernel.org>; Tue, 27 Nov 2018 07:30:12 +0000 (UTC)
DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org CAA1B21104
Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=kernel.org
Authentication-Results: mail.kernel.org; spf=none smtp.mailfrom=linux-kernel-owner@vger.kernel.org
Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand
        id S1729103AbeK0S1I (ORCPT
        <rfc822;linux-kernel@archiver.kernel.org>);
        Tue, 27 Nov 2018 13:27:08 -0500
Received: from mx2.suse.de ([195.135.220.15]:58204 "EHLO mx1.suse.de"
        rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP
        id S1728977AbeK0S1I (ORCPT <rfc822;linux-kernel@vger.kernel.org>);
        Tue, 27 Nov 2018 13:27:08 -0500
X-Virus-Scanned: by amavisd-new at test-mx.suse.de
Received: from relay2.suse.de (unknown [195.135.220.254])
        by mx1.suse.de (Postfix) with ESMTP id 90C60AEA6;
        Tue, 27 Nov 2018 07:30:09 +0000 (UTC)
Date:   Tue, 27 Nov 2018 08:30:07 +0100 (CET)
From:   Jiri Kosina <jikos@kernel.org>
To:     Thomas Gleixner <tglx@linutronix.de>
cc:     Tim Chen <tim.c.chen@linux.intel.com>,
        Ingo Molnar <mingo@kernel.org>,
        LKML <linux-kernel@vger.kernel.org>, x86@kernel.org,
        Peter Zijlstra <peterz@infradead.org>,
        Andy Lutomirski <luto@kernel.org>,
        Linus Torvalds <torvalds@linux-foundation.org>,
        Tom Lendacky <thomas.lendacky@amd.com>,
        Josh Poimboeuf <jpoimboe@redhat.com>,
        Andrea Arcangeli <aarcange@redhat.com>,
        David Woodhouse <dwmw@amazon.co.uk>,
        Andi Kleen <ak@linux.intel.com>,
        Dave Hansen <dave.hansen@intel.com>,
        Casey Schaufler <casey.schaufler@intel.com>,
        Asit Mallick <asit.k.mallick@intel.com>,
        Arjan van de Ven <arjan@linux.intel.com>,
        Jon Masters <jcm@redhat.com>,
        Waiman Long <longman9394@gmail.com>,
        Greg KH <gregkh@linuxfoundation.org>,
        Dave Stewart <david.c.stewart@intel.com>,
        Kees Cook <keescook@chromium.org>
Subject: Re: [patch 20/24] x86/speculation: Split out TIF update
In-Reply-To: <alpine.DEB.2.21.1811270809450.1682@nanos.tec.linutronix.de>
Message-ID: <nycvar.YFH.7.76.1811270820050.21108@cbobk.fhfr.pm>
References: <20181121201430.559770965@linutronix.de> <20181121201724.227260385@linutronix.de> <f976eb35-5dcd-387e-eb29-f7c6636fd17b@linux.intel.com> <alpine.DEB.2.21.1811222352340.1665@nanos.tec.linutronix.de> <20181123073735.GA12959@gmail.com>
 <c51dd20a-2cea-1bd1-bee7-48ca25f9bdb9@linux.intel.com> <alpine.DEB.2.21.1811262244510.1682@nanos.tec.linutronix.de> <nycvar.YFH.7.76.1811270800090.21108@cbobk.fhfr.pm> <alpine.DEB.2.21.1811270809450.1682@nanos.tec.linutronix.de>
User-Agent: Alpine 2.21 (LSU 202 2017-01-01)
MIME-Version: 1.0
Content-Type: text/plain; charset=US-ASCII
Sender: linux-kernel-owner@vger.kernel.org
Precedence: bulk
List-ID: <linux-kernel.vger.kernel.org>
X-Mailing-List: linux-kernel@vger.kernel.org

On Tue, 27 Nov 2018, Thomas Gleixner wrote:

> That's racy and does not prevent the situation because the TIF flags are
> updated befor the UPDATE bit is set. 

> So __speculation_ctrl_update() might see the new bits, but not 
> TIF_SPEC_UPDATE. 

Hm, right, scratch that. We'd need to do that before updating TIF_SPEC_IB 
in task_update_spec_tif(), but that has the opposite ordering issue.

Thanks,

-- 
Jiri Kosina
SUSE Labs