From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752163AbaEUOVU (ORCPT ); Wed, 21 May 2014 10:21:20 -0400 Received: from mail.skyhub.de ([78.46.96.112]:55857 "EHLO mail.skyhub.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751395AbaEUOVS (ORCPT ); Wed, 21 May 2014 10:21:18 -0400 Date: Wed, 21 May 2014 16:20:55 +0200 From: Borislav Petkov To: Jiri Kosina Cc: Steven Rostedt , "H. Peter Anvin" , Linus Torvalds , linux-kernel@vger.kernel.org, x86@kernel.org, Salman Qazi , Ingo Molnar , Michal Hocko , Vojtech Pavlik , Petr Tesarik , Petr Mladek , Andy Lutomirski Subject: Re: 64bit x86: NMI nesting still buggy? Message-ID: <20140521142055.GH21205@pd.tnic> References: <20140429100345.3f76a5bd@gandalf.local.home> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.5.23 (2014-03-12) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed, May 21, 2014 at 03:42:24PM +0200, Jiri Kosina wrote: > Alright, Andy's iret optimization efforts do immediately bring a > followup question -- why is this not a problem with iret-based return > from #MC possibly interrupting NMI? Yeah, and frankly, I don't see this nesting fun at all protected against a #MC interrupting it at any point actually. Because once the #MC handler returns, it goes into paranoid_exit and that place doesn't account for NMIs at all, AFAICS. Which would mean: * NMI goes off * MCE happens, we switch to machine_check which is paranoidzeroentry * #MC handler is done -> paranoid_exit -> IRET -> boom! Or if not "boom", at least, the NMI gets forgotten. Am I missing something? -- Regards/Gruss, Boris. Sent from a fat crate under my desk. Formatting is fine. --