From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1759861AbYDUPPk (ORCPT ); Mon, 21 Apr 2008 11:15:40 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1755075AbYDUPPK (ORCPT ); Mon, 21 Apr 2008 11:15:10 -0400 Received: from terminus.zytor.com ([198.137.202.10]:47484 "EHLO terminus.zytor.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754887AbYDUPPI (ORCPT ); Mon, 21 Apr 2008 11:15:08 -0400 Message-ID: <480CADD3.3010209@zytor.com> Date: Mon, 21 Apr 2008 11:08:03 -0400 From: "H. Peter Anvin" User-Agent: Thunderbird 2.0.0.12 (X11/20080226) MIME-Version: 1.0 To: Mathieu Desnoyers CC: Pavel Machek , mingo@elte.hu, akpm@osdl.org, Jeremy Fitzhardinge , Steven Rostedt , "Frank Ch. Eigler" , linux-kernel@vger.kernel.org Subject: Re: [RFC PATCH] x86 NMI-safe INT3 and Page Fault (v5) References: <20080417165839.GA25198@Krystal> <20080417165944.GB25198@Krystal> <20080417201410.GB31616@Krystal> <20080421140054.GB4685@ucw.cz> <480CA337.3090709@zytor.com> <20080421150825.GA4070@Krystal> In-Reply-To: <20080421150825.GA4070@Krystal> Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Mathieu Desnoyers wrote: > > Just to be clear : the added cost on normal interrupt return is to add a > supplementary test of the thread flags already loaded in registers and > a conditional branch. This is used to detect if we are nested over an > NMI handler. I doubt anyone ever notice an impact caused by this added > test/branch. > Why the **** would you do this except in the handful of places where you actually *could* be nested over an NMI handler (basically #MC, #DB and INT3)? -hpa