From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S934377AbZFOVHI (ORCPT ); Mon, 15 Jun 2009 17:07:08 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S934318AbZFOVGt (ORCPT ); Mon, 15 Jun 2009 17:06:49 -0400 Received: from claw.goop.org ([74.207.240.146]:45471 "EHLO claw.goop.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S934315AbZFOVGr (ORCPT ); Mon, 15 Jun 2009 17:06:47 -0400 Message-ID: <4A36B7DE.9000007@goop.org> Date: Mon, 15 Jun 2009 14:06:38 -0700 From: Jeremy Fitzhardinge User-Agent: Mozilla/5.0 (X11; U; Linux x86_64; en-US; rv:1.9.1b3pre) Gecko/20090513 Fedora/3.0-2.3.beta2.fc11 Thunderbird/3.0b2 MIME-Version: 1.0 To: Linus Torvalds CC: Ingo Molnar , Mathieu Desnoyers , mingo@redhat.com, hpa@zytor.com, paulus@samba.org, acme@redhat.com, linux-kernel@vger.kernel.org, a.p.zijlstra@chello.nl, penberg@cs.helsinki.fi, vegard.nossum@gmail.com, efault@gmx.de, npiggin@suse.de, tglx@linutronix.de, linux-tip-commits@vger.kernel.org Subject: Re: [tip:perfcounters/core] perf_counter: x86: Fix call-chain support to use NMI-safe methods References: <20090615171845.GA7664@elte.hu> <20090615180527.GB4201@Krystal> <20090615183649.GA16999@elte.hu> <4A36ABB5.1040109@goop.org> In-Reply-To: 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 On 06/15/09 13:27, Linus Torvalds wrote: > On Mon, 15 Jun 2009, Jeremy Fitzhardinge wrote: > >> We have to restore the usermode %gs somewhere... >> > > None of this is useful for user-mode return _anyway_, since you have to > restore %cs/%ss too. At that point, you have to use iret. > Ah, right. I'd even looked at that at one point, when I was investigating optimising kernel->kernel exit paths (I'd decided it wasn't worth it for its own sake, since they simply don't happen that often). J