Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754596Ab0ARNQP (ORCPT ); Mon, 18 Jan 2010 08:16:15 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1751490Ab0ARNQO (ORCPT ); Mon, 18 Jan 2010 08:16:14 -0500 Received: from bombadil.infradead.org ([18.85.46.34]:33408 "EHLO bombadil.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751056Ab0ARNQN (ORCPT ); Mon, 18 Jan 2010 08:16:13 -0500 Subject: Re: [RFC] [PATCH 1/7] User Space Breakpoint Assistance Layer (UBP) From: Peter Zijlstra To: Avi Kivity Cc: ananth@in.ibm.com, Jim Keniston , Srikar Dronamraju , Ingo Molnar , Arnaldo Carvalho de Melo , utrace-devel , Frederic Weisbecker , Masami Hiramatsu , Maneesh Soni , Mark Wielaard , LKML In-Reply-To: <4B5455FF.7010409@redhat.com> References: <20100111122521.22050.3654.sendpatchset@srikar.in.ibm.com> <20100111122529.22050.32596.sendpatchset@srikar.in.ibm.com> <1263467289.4244.288.camel@laptop> <1263498366.4875.25.camel@localhost.localdomain> <1263546228.4244.343.camel@laptop> <20100115093831.GC26396@in.ibm.com> <1263549014.4244.374.camel@laptop> <4B53213C.9050303@redhat.com> <1263739939.557.20938.camel@twins> <4B5325CF.5000001@redhat.com> <1263740593.557.20967.camel@twins> <4B53661A.9090907@redhat.com> <1263800752.4283.19.camel@laptop> <4B543F93.3060509@redhat.com> <1263815072.4283.305.camel@laptop> <4B544D7C.2060708@redhat.com> <1263816396.4283.361.camel@laptop> <4B544F8E.1080603@redhat.com> <1263816857.4283.381.camel@laptop> <4B5455FF.7010409@redhat.com> Content-Type: text/plain; charset="UTF-8" Date: Mon, 18 Jan 2010 14:15:51 +0100 Message-ID: <1263820551.4283.499.camel@laptop> Mime-Version: 1.0 X-Mailer: Evolution 2.28.1 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1582 Lines: 37 On Mon, 2010-01-18 at 14:37 +0200, Avi Kivity wrote: > On 01/18/2010 02:14 PM, Peter Zijlstra wrote: > > > >> Well, the alternatives are very unappealing. Emulation and > >> single-stepping are going to be very slow compared to a couple of jumps. > >> > > With CPL2 or RPL on user segments the protection issue seems to be > > manageable for running the instructions from kernel space. > > > > CPL2 gives unrestricted access to the kernel address space; and RPL does > not affect page level protection. Segment limits don't work on x86-64. > But perhaps I missed something - these things are tricky. So setting RPL to 3 on the user segments allows access to kernel pages just fine? How useful.. :/ > It should be possible to translate the instruction into an address space > check, followed by the action, but that's still slower due to privilege > level switches. Well, if you manage to do the address validation you don't need the priv level switch anymore, right? Are the ins encodings sane enough to recognize mem parameters without needing to know the actual ins? How about using a hw-breakpoint to close the gap for the inline single step? You could even re-insert the int3 lazily when you need the hw-breakpoint again. It would consume one hw-breakpoint register for each task/cpu that has probes though.. -- 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/