Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S932491AbaD2ODv (ORCPT ); Tue, 29 Apr 2014 10:03:51 -0400 Received: from cdptpa-outbound-snat.email.rr.com ([107.14.166.226]:63829 "EHLO cdptpa-oedge-vip.email.rr.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1757454AbaD2ODu (ORCPT ); Tue, 29 Apr 2014 10:03:50 -0400 Date: Tue, 29 Apr 2014 10:03:45 -0400 From: Steven Rostedt To: Jiri Kosina Cc: "H. Peter Anvin" , Linus Torvalds , linux-kernel@vger.kernel.org, x86@kernel.org, Salman Qazi , Ingo Molnar , Michal Hocko , Borislav Petkov , Vojtech Pavlik , Petr Tesarik , Petr Mladek Subject: Re: 64bit x86: NMI nesting still buggy? Message-ID: <20140429100345.3f76a5bd@gandalf.local.home> In-Reply-To: References: X-Mailer: Claws Mail 3.9.3 (GTK+ 2.24.22; x86_64-pc-linux-gnu) MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit X-RR-Connecting-IP: 107.14.168.130:25 X-Cloudmark-Score: 0 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue, 29 Apr 2014 15:05:55 +0200 (CEST) Jiri Kosina wrote: > According to 38.4 of [1], when SMM mode is entered while the CPU is > handling NMI, the end result might be that upon exit from SMM, NMIs will > be re-enabled and latched NMI delivered as nested [2]. Note, if this were true, then the x86_64 hardware would be extremely buggy. That's because NMIs are not made to be nested. If SMM's come in during an NMI and re-enables the NMI, then *all* software would break. That would basically make NMIs useless. The only time I've ever witness problems (and I stress NMIs all the time), is when the NMI itself does a fault. Which my patch set handles properly. I've also stressed this on boxes that do have SMIs and SMMs. Now, you can have a bad BIOS that does re-enable NMIs from SMMs or SMIs, but then you need to take that up with your vendor. -- Steve -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/