Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752916AbbLJVJj (ORCPT ); Thu, 10 Dec 2015 16:09:39 -0500 Received: from mail-ob0-f176.google.com ([209.85.214.176]:36261 "EHLO mail-ob0-f176.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751265AbbLJVJi (ORCPT ); Thu, 10 Dec 2015 16:09:38 -0500 MIME-Version: 1.0 In-Reply-To: References: From: Andy Lutomirski Date: Thu, 10 Dec 2015 13:09:18 -0800 Message-ID: Subject: Re: [PATCH 1/1] Fix int1 recursion when no perf_bp_event is registeredy To: Thomas Gleixner Cc: Jeff Merkey , LKML , Ingo Molnar , "H. Peter Anvin" , X86 ML , Peter Zijlstra , Andy Lutomirski , Masami Hiramatsu , Steven Rostedt , Borislav Petkov , Jiri Olsa Content-Type: text/plain; charset=UTF-8 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1542 Lines: 33 On Thu, Dec 10, 2015 at 12:49 PM, Thomas Gleixner wrote: > On Thu, 10 Dec 2015, Andy Lutomirski wrote: >> On brief inspection, this smells like a microcode bug. Can you send >> /proc/cpuinfo output? >> >> If this is the issue, I'm not sure we want to be in the business of >> working around localized microcode bugs and, if we do, then I think we >> should explicitly detect the bug and log about it. > > I think we should handle such stuff gracefully. Yes, we should log it > and we also should check what the contents of the debug registers are. > > If dr7 has a break point enabled w/o perf having one installed then we > know that someone did a horrible hackery .... I mis-read this. I don't think this is the microcode bug. Do we know what the actual problem is? Jeff, how did you trigger this? If it's lazy DR switching (which I haven't looked at the details of), then it seems that this could just be triggered by some unfortunate combination of perf config and context switching). But, if so, then I think that the proposed fix is wrong -- shouldn't we fix dr7 rather than fudging RF to work around this instance of the problem? After all, if we're hitting this condition in a tight userspace loop, we're going to destroy performance unless we fix dr7. --Andy -- 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/