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=-2.0 required=3.0 tests=DKIM_INVALID,DKIM_SIGNED, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS, URIBL_BLOCKED,USER_AGENT_SANE_1 autolearn=no 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 9603CC34047 for ; Wed, 19 Feb 2020 17:34:25 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 67C022465D for ; Wed, 19 Feb 2020 17:34:25 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=fail reason="signature verification failed" (2048-bit key) header.d=infradead.org header.i=@infradead.org header.b="Hm0Lw1D/" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726691AbgBSReY (ORCPT ); Wed, 19 Feb 2020 12:34:24 -0500 Received: from bombadil.infradead.org ([198.137.202.133]:45108 "EHLO bombadil.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726551AbgBSReX (ORCPT ); Wed, 19 Feb 2020 12:34:23 -0500 DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=infradead.org; s=bombadil.20170209; h=In-Reply-To:Content-Type:MIME-Version :References:Message-ID:Subject:Cc:To:From:Date:Sender:Reply-To: Content-Transfer-Encoding:Content-ID:Content-Description; bh=2P6Ws3RkPs8vzqQG8mBEIrnxkKqiE7dFwfIH2EVwUnM=; b=Hm0Lw1D/oQlx5O9Z44lRzvi5i8 S7PAX5z1ivDMlBCEzoFGozFeX3weNrthcgfVSCgrujqySa7S5ILzS99tXV3qmb5XnbtVDAl5o7sTO vlQut+G4rrX56/uxzmOieWFDhKeMKlIbbXZIi13WJOY9YhKZ3qe1xglpRgCHlG7BH9XjaID4EyqlT m+LHNOCydRn8YIQLbGVJLrrnI3ztmILiahomJvR14ECSwBi14a8eIMq5WpNpHg5064/qbkUcXxd84 gX+4BVkGJXSKhaCOhhyWdnd9Hdra/uga2t0UhyWOTY+Vmbzq9bPSbc+yYJ2eTfud/J+xf5axEDerH G7FUaDNA==; Received: from j217100.upc-j.chello.nl ([24.132.217.100] helo=noisy.programming.kicks-ass.net) by bombadil.infradead.org with esmtpsa (Exim 4.92.3 #3 (Red Hat Linux)) id 1j4TEW-0002wP-Tq; Wed, 19 Feb 2020 17:34:01 +0000 Received: from hirez.programming.kicks-ass.net (hirez.programming.kicks-ass.net [192.168.1.225]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (Client did not present a certificate) by noisy.programming.kicks-ass.net (Postfix) with ESMTPS id DE66A300565; Wed, 19 Feb 2020 18:32:05 +0100 (CET) Received: by hirez.programming.kicks-ass.net (Postfix, from userid 1000) id 520CF202287CB; Wed, 19 Feb 2020 18:33:58 +0100 (CET) Date: Wed, 19 Feb 2020 18:33:58 +0100 From: Peter Zijlstra To: Andy Lutomirski Cc: Borislav Petkov , LKML , linux-arch , Steven Rostedt , Ingo Molnar , Joel Fernandes , Greg KH , gustavo@embeddedor.com, Thomas Gleixner , paulmck@kernel.org, Josh Triplett , Mathieu Desnoyers , Lai Jiangshan , Tony Luck , Frederic Weisbecker , Dan Carpenter , Masami Hiramatsu Subject: Re: [PATCH v3 02/22] x86,mce: Delete ist_begin_non_atomic() Message-ID: <20200219173358.GP18400@hirez.programming.kicks-ass.net> References: <20200219144724.800607165@infradead.org> <20200219150744.488895196@infradead.org> <20200219171309.GC32346@zn.tnic> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.10.1 (2018-07-13) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed, Feb 19, 2020 at 09:21:48AM -0800, Andy Lutomirski wrote: > On Wed, Feb 19, 2020 at 9:13 AM Borislav Petkov wrote: > > > > On Wed, Feb 19, 2020 at 03:47:26PM +0100, Peter Zijlstra wrote: > > > Subject: Re: [PATCH v3 02/22] x86,mce: Delete ist_begin_non_atomic() > > > > x86/mce: ... > > > > > It is an abomination; and in prepration of removing the whole > > > ist_enter() thing, it needs to go. > > > > > > Convert #MC over to using task_work_add() instead; it will run the > > > same code slightly later, on the return to user path of the same > > > exception. > > > > That's fine because the error happened in userspace. > > Unless there is a signal pending and the signal setup code is about to > hit the same failed memory. I suppose we can just treat cases like > this as "oh well, time to kill the whole system". > > But we should genuinely agree that we're okay with deferring this handling. It doesn't delay much. The moment it does that local_irq_enable() it's subject to preemption, just like it is on the return to user path. Do you really want to create code that unwinds enough of nmi_enter() to get you to a preemptible context? *shudder*