From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: 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=HEADER_FROM_DIFFERENT_DOMAINS, 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 C1002C43441 for ; Mon, 26 Nov 2018 20:58:35 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 6B514208E4 for ; Mon, 26 Nov 2018 20:58:35 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 6B514208E4 Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=linutronix.de 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 S1727337AbeK0Hx4 (ORCPT ); Tue, 27 Nov 2018 02:53:56 -0500 Received: from Galois.linutronix.de ([146.0.238.70]:55828 "EHLO Galois.linutronix.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1727105AbeK0Hxz (ORCPT ); Tue, 27 Nov 2018 02:53:55 -0500 Received: from p4fea46ac.dip0.t-ipconnect.de ([79.234.70.172] helo=nanos) by Galois.linutronix.de with esmtpsa (TLS1.2:DHE_RSA_AES_256_CBC_SHA256:256) (Exim 4.80) (envelope-from ) id 1gRNxc-0000w7-9S; Mon, 26 Nov 2018 21:58:28 +0100 Date: Mon, 26 Nov 2018 21:58:27 +0100 (CET) From: Thomas Gleixner To: Andrea Arcangeli cc: Linus Torvalds , Linux List Kernel Mailing , the arch/x86 maintainers , Peter Zijlstra , Andrew Lutomirski , Jiri Kosina , thomas.lendacky@amd.com, Josh Poimboeuf , David Woodhouse , Tim Chen , Andi Kleen , dave.hansen@intel.com, Casey Schaufler , "Mallick, Asit K" , "Van De Ven, Arjan" , jcm@redhat.com, longman9394@gmail.com, Greg KH , david.c.stewart@intel.com, Kees Cook Subject: Re: [patch V2 27/28] x86/speculation: Add seccomp Spectre v2 user space protection mode In-Reply-To: <20181126204842.GC16136@redhat.com> Message-ID: References: <20181125183328.318175777@linutronix.de> <20181125185006.051663132@linutronix.de> <20181126204842.GC16136@redhat.com> User-Agent: Alpine 2.21 (DEB 202 2017-01-01) 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 Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Mon, 26 Nov 2018, Andrea Arcangeli wrote: > Hello, > > On Sun, Nov 25, 2018 at 11:28:59PM +0100, Thomas Gleixner wrote: > > Indeed. Just checked the documentation again, it's also not clear whether > > IBPB is required if STIPB is in use. > > I tried to ask this question too earlier: > > https://lkml.kernel.org/r/20181119234528.GJ29258@redhat.com > > If the BTB mistraining in SECCOMP context with STIBP set in SPEC_CTRL, > can still influence the hyperthreading sibling after STIBP is cleared, > IBPB is needed before clearing STIBP. Otherwise it's not. Unless told > otherwise, it'd be safe to assume IBPB is needed in such case. IBPB is still issued. I won't change that before we have clarification. But I doubt it's necessary. STIBP seems to be a rather big hammer. Thanks, tglx