Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755550AbcDNN2h (ORCPT ); Thu, 14 Apr 2016 09:28:37 -0400 Received: from mx2.suse.de ([195.135.220.15]:34968 "EHLO mx2.suse.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753642AbcDNN2g (ORCPT ); Thu, 14 Apr 2016 09:28:36 -0400 Date: Thu, 14 Apr 2016 15:28:31 +0200 (CEST) From: Miroslav Benes To: Jessica Yu cc: Michael Ellerman , linuxppc-dev@ozlabs.org, bsingharora@gmail.com, duwe@lst.de, linux-kernel@vger.kernel.org, rostedt@goodmis.org, kamalesh@linux.vnet.ibm.com, pmladek@suse.com, jikos@kernel.org, live-patching@vger.kernel.org Subject: Re: Live patching for powerpc In-Reply-To: <20160413182228.GA16776@packer-debian-8-amd64.digitalocean.com> Message-ID: References: <1460552003-15409-1-git-send-email-mpe@ellerman.id.au> <20160413182228.GA16776@packer-debian-8-amd64.digitalocean.com> User-Agent: Alpine 2.00 (LNX 1167 2008-08-23) MIME-Version: 1.0 Content-Type: TEXT/PLAIN; charset=US-ASCII Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2275 Lines: 57 On Wed, 13 Apr 2016, Jessica Yu wrote: > +++ Miroslav Benes [13/04/16 15:01 +0200]: > > On Wed, 13 Apr 2016, Michael Ellerman wrote: > > > > > This series adds live patching support for powerpc (ppc64le only ATM). > > > > > > It's unchanged since the version I posted on March 24, with the exception > > > that > > > I've dropped the first patch, which was a testing-only patch. > > > > > > If there's no further comments I'll put this in a topic branch in the next > > > day > > > or two and Jiri & I will both merge that into next. > > > > Hi, > > > > I'll definitely give it a proper look today or tomorrow, but there is one > > thing that needs to be solved. The patch set from Jessica reworking > > relocations for live patching is now merged in our for-next branch. This > > means that we need to find out if there is something in struct > > mod_arch_specific for powerpc which needs to be preserved and do it. > > > > I took a look around the powerpc module.c code and it looks like the > mod_arch_specific stuff should be fine, since it is statically allocated > in the module struct (unlike the situation in s390, where > mod->arch.syminfo was vmalloc'd and we had to delay the free). > However I'm not familiar with the powerpc code so I need to dig around > a bit more to be 100% sure. I came to the same conclusion. There is only struct bug_entry *bug_table in mod_arch_specific but it looks unimportant wrt relocations. > A second concern I have is that apply_relocate_add() relies on > sections like .stubs and .toc (for 64-bit) and .init.plt and .plt > sections (for 32-bit). In order for apply_relocate_add() to work for > livepatch, we must make sure these sections aren't thrown away and are > not in init module memory since this memory will be freed at the end > of module load (see how INIT_OFFSET_MASK is used in kernel/module.c). > As long as these sections are placed in module core memory, we will be > OK. I need to think about this a bit more. I knew I shouldn't have opened arch/powerpc/kernel/module*.c. We could always hack sh_flags of those sections in module_arch_frob_sections() to make them stay. Miroslav > > Third and unrelated comment: the klp_write_module_reloc stub isn't > needed anymore :-) > > Thanks, > Jessica >