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=-0.8 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_PASS,URIBL_BLOCKED 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 B9785C5CFC1 for ; Tue, 19 Jun 2018 06:23:48 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 7B3D2208B3 for ; Tue, 19 Jun 2018 06:23:48 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 7B3D2208B3 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 S965437AbeFSGXq (ORCPT ); Tue, 19 Jun 2018 02:23:46 -0400 Received: from Galois.linutronix.de ([146.0.238.70]:56326 "EHLO Galois.linutronix.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S965152AbeFSGXp (ORCPT ); Tue, 19 Jun 2018 02:23:45 -0400 Received: from p4fea482e.dip0.t-ipconnect.de ([79.234.72.46] helo=nanos.glx-home) by Galois.linutronix.de with esmtpsa (TLS1.2:DHE_RSA_AES_256_CBC_SHA256:256) (Exim 4.80) (envelope-from ) id 1fVA3L-0000Zv-NE; Tue, 19 Jun 2018 08:23:43 +0200 Date: Tue, 19 Jun 2018 08:23:40 +0200 (CEST) From: Thomas Gleixner To: Andy Lutomirski cc: Siarhei.Liakh@concurrent-rt.com, LKML , X86 ML , Ingo Molnar , "H. Peter Anvin" , Borislav Petkov Subject: Re: [PATCH] x86: Call fixup_exception() before notify_die() in math_error() In-Reply-To: Message-ID: References: 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, 18 Jun 2018, Andy Lutomirski wrote: > On Thu, Jun 14, 2018 at 10:10 PM Siarhei Liakh > wrote: > > > > fpu__drop() has an explicit fwait which under some conditions can trigger > > a fixable FPU exception while in kernel. Thus, we should attempt to fixup > > the exception first, and only call notify_die() if the fixup failed just > > like in do_general_protection(). The original call sequence incorrectly > > triggers KDB entry on debug kernels under particular FPU-intensive > > workloads. This issue had been privately observed, fixed, and tested > > on 4.9.98, while this patch brings the fix to the upstream. > > Reviewed-by: Andy Lutomirski > > With the caveat that you are perpetuating what is arguably a bug in > some of the other entries: math_error() can now be called with IRQs > off and return with IRQs on. If we actually start asserting good > behavior in the entry code, we'll need to fix this. Confused. math_error() is still invoked with interrupts off. What's different now is that notify_die() is called with interrupts conditionally enabled while upstream it's always called with interrupts disabled. Thanks, tglx