Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754970Ab0A0OAH (ORCPT ); Wed, 27 Jan 2010 09:00:07 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S932152Ab0A0OAC (ORCPT ); Wed, 27 Jan 2010 09:00:02 -0500 Received: from hrndva-omtalb.mail.rr.com ([71.74.56.125]:56193 "EHLO hrndva-omtalb.mail.rr.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752088Ab0A0N77 (ORCPT ); Wed, 27 Jan 2010 08:59:59 -0500 X-Authority-Analysis: v=1.0 c=1 a=7U3hwN5JcxgA:10 a=0kZOHi1rR7WaGBm7pV0A:9 a=a9Whc8VzzVObCBgTpCQA:7 a=UWmenQWppCumnNqqBO0ThMow-lgA:4 X-Cloudmark-Score: 0 X-Originating-IP: 74.67.89.75 Subject: Re: linux-next: add utrace tree From: Steven Rostedt Reply-To: rostedt@goodmis.org To: Linus Torvalds Cc: Peter Zijlstra , Tom Tromey , Kyle Moffett , "Frank Ch. Eigler" , Oleg Nesterov , Andrew Morton , Stephen Rothwell , Fr??d??ric Weisbecker , LKML , Arnaldo Carvalho de Melo , linux-next@vger.kernel.org, "H. Peter Anvin" , utrace-devel@redhat.com, Thomas Gleixner , JimKeniston , Arjan van de Ven In-Reply-To: References: <20100121013822.28781960.sfr@canb.auug.org.au> <20100122005147.GD22003@redhat.com> <20100121170541.7425ff10.akpm@linux-foundation.org> <20100122182827.GA13185@redhat.com> <20100122200129.GG22003@redhat.com> <20100122221348.GA4263@redhat.com> <1264575134.4283.1983.camel@laptop> Content-Type: text/plain; charset="ISO-8859-15" Organization: Kihon Technologies Inc. Date: Wed, 27 Jan 2010 08:59:52 -0500 Message-ID: <1264600792.31321.464.camel@gandalf.stny.rr.com> 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: 1591 Lines: 41 [ Added Arjan ] On Wed, 2010-01-27 at 02:43 -0800, Linus Torvalds wrote: > > On Wed, 27 Jan 2010, Peter Zijlstra wrote: > > > > Right, so you're going to love uprobes, which does exactly that. The > > current proposal is overwriting the target instruction with an INT3 and > > injecting an extra vma into the target process's address space > > containing the original instruction(s) and possible jumps back to the > > old code stream. > > Just out of interest, how does it handle the threading issue? > > Last I saw, at least some CPU people were _very_ nervous about overwriting > instructions if another CPU might be just about to execute them. I think the issue was that ring 0 was never meant to do that, where as, ring 3 does it all the time. Doesn't the dynamic library modify its text? -- Steve > > Even the "overwrite only the first byte with 'int3'" made them go "umm, I > need to talk to some core CPU people to see if that's ok". They mumble > about possible CPU errata, I$ coherency, instruction retry etc. > > I realize kprobes does this very thing, but kprobes is esoteric stuff and > doesn't have much choice. In user space, you _could_ do the modification > on a different physical page and then just switch the page table entry > instead, and not get into the whole D$/I$ coherency thing at all. > > Linus -- 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/