From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S932082AbVKEPhv (ORCPT ); Sat, 5 Nov 2005 10:37:51 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S932084AbVKEPhv (ORCPT ); Sat, 5 Nov 2005 10:37:51 -0500 Received: from defout.telus.net ([199.185.220.240]:11215 "EHLO priv-edtnes46.telusplanet.net") by vger.kernel.org with ESMTP id S932082AbVKEPhu (ORCPT ); Sat, 5 Nov 2005 10:37:50 -0500 From: Andi Kleen To: Andrea Arcangeli Subject: Re: disable tsc with seccomp Date: Sat, 5 Nov 2005 16:37:44 +0100 User-Agent: KMail/1.8 Cc: linux-kernel@vger.kernel.org, Andrew Morton References: <20051105134727.GF18861@opteron.random> In-Reply-To: <20051105134727.GF18861@opteron.random> MIME-Version: 1.0 Content-Type: text/plain; charset="iso-8859-1" Content-Transfer-Encoding: 7bit Content-Disposition: inline Message-Id: <200511051637.44432.ak@suse.de> Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org On Saturday 05 November 2005 14:47, Andrea Arcangeli wrote: > Hello, > > This changeset is backing out an useful feature I implemented some month > ago: > > http://kernel.org/hg/linux-2.6/?cs=2fd4e5f089df > > Anything that can strengthen security is needed, the covert channels are > theoretically possible and this is a fact, you don't need hyperthreading > for that. It was useless, you can get exactly the same information by using RDPMC on perfctr 0 which always runs the NMI watchdog and counts all cycles too. And even with that I don't want to have such checks in the context switch for something that is at best theoretical. Letting it in would open the floodgates for making the context switch really slow long term. -Andi