From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1762363AbYDUOaq (ORCPT ); Mon, 21 Apr 2008 10:30:46 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1760691AbYDUOa2 (ORCPT ); Mon, 21 Apr 2008 10:30:28 -0400 Received: from terminus.zytor.com ([198.137.202.10]:56509 "EHLO terminus.zytor.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1760336AbYDUOa1 (ORCPT ); Mon, 21 Apr 2008 10:30:27 -0400 Message-ID: <480CA337.3090709@zytor.com> Date: Mon, 21 Apr 2008 10:22:47 -0400 From: "H. Peter Anvin" User-Agent: Thunderbird 2.0.0.12 (X11/20080226) MIME-Version: 1.0 To: Pavel Machek CC: Mathieu Desnoyers , 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> In-Reply-To: <20080421140054.GB4685@ucw.cz> 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 Pavel Machek wrote: > On Thu 2008-04-17 16:14:10, Mathieu Desnoyers wrote: >> (hopefully finally CCing LKML) :) >> >> Implements an alternative iret with popf and return so trap and exception >> handlers can return to the NMI handler without issuing iret. iret would cause >> NMIs to be reenabled prematurely. x86_32 uses popf and far return. x86_64 has to >> copy the return instruction pointer to the top of the previous stack, issue a >> popf, loads the previous esp and issue a near return (ret). > > sounds expensive. Does it slow down normal loads? > It should *only* be used to return from NMI, #MC or INT3 (breakpoint), which should never happen in normal operation, and even then only when interrupting another NMI or #MC handler. -hpa