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 C1DF8C282C2 for ; Fri, 25 Jan 2019 15:39:23 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 9A6D0218DE for ; Fri, 25 Jan 2019 15:39:23 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727998AbfAYPjV (ORCPT ); Fri, 25 Jan 2019 10:39:21 -0500 Received: from Galois.linutronix.de ([146.0.238.70]:38711 "EHLO Galois.linutronix.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726265AbfAYPjU (ORCPT ); Fri, 25 Jan 2019 10:39:20 -0500 Received: from [79.234.67.100] (helo=nanos) by Galois.linutronix.de with esmtpsa (TLS1.2:DHE_RSA_AES_256_CBC_SHA256:256) (Exim 4.80) (envelope-from ) id 1gn3Zb-0006TU-Oe; Fri, 25 Jan 2019 16:39:15 +0100 Date: Fri, 25 Jan 2019 16:39:09 +0100 (CET) From: Thomas Gleixner To: Zhenzhong Duan cc: linux-kernel@vger.kernel.org, mingo@redhat.com, konrad.wilk@oracle.com, x86@kernel.org, srinivas.eeda@oracle.com, bp@suse.de, tim.c.chen@linux.intel.com, peterz@infradead.org, hpa@zytor.com Subject: Re: [PATCH] x86/speculation: Update TIF_SPEC_IB before ibpb barrier In-Reply-To: Message-ID: References: <48a105d3-fa32-40e4-9775-37d49f42eac0@default> 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 Wed, 23 Jan 2019, Thomas Gleixner wrote: > On Fri, 18 Jan 2019, Zhenzhong Duan wrote: > > > When a task is set for updating TIF_SPEC_IB throuth SECCOMP by others > > and it's scheduled in the first time, a stale TIF_SPEC_IB value is > > picked in cond_ibpb(). This is due to TIF_SPEC_IB is updated later at > > __switch_to_xtra(). > > > > Add an extra call to speculation_ctrl_update_tif() to update it before > > IBPB barrier. > > Errm. No. It adds that call to speculation_ctrl_update_tif() for every > mm switch, most of the time for nothing. > > If at all, and we discussed that before and decided not to worry about it > (because it gets fixed up on the next context switch), then you want to > handle ibpb() from there: Actually we need to do that. It's not only the scheduled in first problem. That whole thing might become completely stale in either direction. Care to whip up a patch? Thanks, tglx