Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S261462AbVENTVu (ORCPT ); Sat, 14 May 2005 15:21:50 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S261464AbVENTVu (ORCPT ); Sat, 14 May 2005 15:21:50 -0400 Received: from mustang.oldcity.dca.net ([216.158.38.3]:16846 "HELO mustang.oldcity.dca.net") by vger.kernel.org with SMTP id S261462AbVENTVr (ORCPT ); Sat, 14 May 2005 15:21:47 -0400 Subject: Re: Hyper-Threading Vulnerability From: Lee Revell To: Arjan van de Ven Cc: Alan Cox , Dave Jones , Matt Mackall , Andy Isaacson , Andi Kleen , "Richard F. Rebel" , Gabor MICSKO , Linux Kernel Mailing List , tytso@mit.edu In-Reply-To: <1116093694.6007.15.camel@laptopd505.fenrus.org> References: <1115963481.1723.3.camel@alderaan.trey.hu> <1116009483.4689.803.camel@rebel.corp.whenu.com> <20050513190549.GB47131@muc.de> <20050513212620.GA12522@hexapodia.org> <20050513215905.GY5914@waste.org> <1116024419.20646.41.camel@localhost.localdomain> <1116025212.6380.50.camel@mindpipe> <20050513232708.GC13846@redhat.com> <1116027488.6380.55.camel@mindpipe> <1116084186.20545.47.camel@localhost.localdomain> <1116088229.8880.7.camel@mindpipe> <1116089068.6007.13.camel@laptopd505.fenrus.org> <1116093396.9141.11.camel@mindpipe> <1116093694.6007.15.camel@laptopd505.fenrus.org> Content-Type: text/plain Date: Sat, 14 May 2005 15:21:44 -0400 Message-Id: <1116098504.9141.31.camel@mindpipe> Mime-Version: 1.0 X-Mailer: Evolution 2.3.1 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1686 Lines: 37 On Sat, 2005-05-14 at 20:01 +0200, Arjan van de Ven wrote: > On Sat, 2005-05-14 at 13:56 -0400, Lee Revell wrote: > > On Sat, 2005-05-14 at 18:44 +0200, Arjan van de Ven wrote: > > > then JACK is terminally broken if it doesn't have a fallback for non- > > > rdtsc cpus. > > > > It does have a fallback, but the selection is done at compile time. It > > uses rdtsc for all x86 CPUs except pre-i586 SMP systems. > > > > Maybe we should check at runtime, > > it's probably a sign that JACK isn't used on SMP systems much, at least > not on the bigger systems (like IBM's x440's) where the tsc *will* > differ wildly between cpus... Correct. The only bug reports we have seen related to the use of the TSC is due to CPU frequency scaling. The fix is to not use it - people who want to use their PC as a DSP for audio probably don't want their processor slowing down anyway. And JACK is targeted at desktop and smaller systems, it would be kind of crazy to run it on a big iron. Well, maybe there are people who like to record sessions or practice guitar in the server room... If gettimeofday is really as cheap as rdtsc on x86_64, we should use it. But it's too expensive for slower x86 systems. Anyway, Andi's fix disables *all* high res timing including gettimeofday. Obviously no multimedia app can tolerate this, so discussing rdtsc is really a red herring. But multimedia apps aren't much in seccomp environments either. Lee - 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/