From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S932817Ab3GKOrM (ORCPT ); Thu, 11 Jul 2013 10:47:12 -0400 Received: from prod-mail-xrelay02.akamai.com ([72.246.2.14]:41711 "EHLO prod-mail-xrelay02.akamai.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1756125Ab3GKOrI (ORCPT ); Thu, 11 Jul 2013 10:47:08 -0400 Message-ID: <51DEC56A.4050001@akamai.com> Date: Thu, 11 Jul 2013 10:47:06 -0400 From: Jason Baron User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:17.0) Gecko/20130330 Thunderbird/17.0.5 MIME-Version: 1.0 To: Steven Rostedt CC: "H. Peter Anvin" , Jiri Kosina , Masami Hiramatsu , Jason Baron , Borislav Petkov , linux-kernel@vger.kernel.org Subject: Re: [RFC] [PATCH 1/2 v2] x86: introduce int3-based instruction patching References: <51DDD3E9.6090601@linux.intel.com> <1373553344.17876.13.camel@gandalf.local.home> In-Reply-To: <1373553344.17876.13.camel@gandalf.local.home> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 07/11/2013 10:35 AM, Steven Rostedt wrote: > On Wed, 2013-07-10 at 14:36 -0700, H. Peter Anvin wrote: >> On 07/10/2013 02:31 PM, Jiri Kosina wrote: >>> If any CPU instruction execution would collide with the patching, >>> it'd be trapped by the int3 breakpoint and redirected to the provided >>> "handler" (which would typically mean just skipping over the patched >>> region, acting as "nop" has been there, in case we are doing nop -> jump >>> and jump -> nop transitions). >>> >> I'm wondering if it would be easier/more general to just return to the >> instruction. The "more general" bit would allow this to be used for >> other things, like alternatives, and perhaps eventually dynamic call >> patching. >> >> Returning to the instruction will, in effect, be a busy-wait for the >> faulted CPU until the patch is complete; more or less what stop_machine >> would do, but only for a CPU which actually strays into the affected region. >> > Wont work for ftrace, as it patches all functions, it even patches > functions used to do the changes. Thus, it would cause a deadlock if a > breakpoint were to spin till the changes were finished. > > -- Steve > > I'm not sure this works for jump labels either. Some tracepoints (which use jump_labels) have interrupts disabled across them. Thus, they will spin with interrupts disabled, while we are trying to issue an IPI. Thanks, -Jason