From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1756270Ab3KFKmA (ORCPT ); Wed, 6 Nov 2013 05:42:00 -0500 Received: from cam-admin0.cambridge.arm.com ([217.140.96.50]:37007 "EHLO cam-admin0.cambridge.arm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1755753Ab3KFKl7 (ORCPT ); Wed, 6 Nov 2013 05:41:59 -0500 Date: Wed, 6 Nov 2013 10:41:10 +0000 From: Will Deacon To: Sandeepa Prabhu Cc: Jiang Liu , Steven Rostedt , Catalin Marinas , Jiang Liu , "linux-arm-kernel@lists.infradead.org" , "linux-kernel@vger.kernel.org" Subject: Re: [PATCH v5 2/7] arm64: introduce interfaces to hotpatch kernel and module code Message-ID: <20131106104110.GC21074@mudshark.cambridge.arm.com> References: <1382109602-27432-1-git-send-email-liuj97@gmail.com> <1382109602-27432-3-git-send-email-liuj97@gmail.com> <20131030001245.GB25346@mudshark.cambridge.arm.com> <527671E9.8040704@gmail.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.5.21 (2010-09-15) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Mon, Nov 04, 2013 at 03:12:56PM +0000, Sandeepa Prabhu wrote: > On 3 November 2013 23:55, Jiang Liu wrote: > > On 10/30/2013 08:12 AM, Will Deacon wrote: > >> On Fri, Oct 18, 2013 at 04:19:56PM +0100, Jiang Liu wrote: > >>> + atomic_set(&text_patch_id, smp_processor_id()); > >>> + ret = stop_machine(aarch64_insn_patch_text_cb, &patch, cpu_online_mask); > >> > >> Instead of doing this, why not instead call aarch64_insn_patch_text_nosync > >> inline, then call kick_all_cpus_sync immediately afterwards, without the > >> need to stop_machine. > > Sandeepa, who is working on kprobe for ARM64, needs the stop_machine() > > mechanism to synchronize all online CPUs, so it's a preparation for > > kprobe. > > I had published kprobes patches for ARM64: > http://lwn.net/Articles/570648/ and using your patcset (v3) for > patching support, it works so far. > I CCed you on my RFC but unfortunately to your huawei email not the gmail. > > I can give a try with kick_all_cpus_sync but wanted to understand this > a bit detail on hows different from stop_machine and how this work. My point was just that for nosync patching, the update to the instruction stream is atomic with respect to instruction fetch, so stop_machine seems a bit overkill. kick_all_cpus can be used to ensure visibility of the new instruction. Jiang Liu seemed to imply that this isn't suitable for kprobes, but I would like to know if/why that is the case. Will