Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S965127Ab3E2RNJ (ORCPT ); Wed, 29 May 2013 13:13:09 -0400 Received: from e06smtp17.uk.ibm.com ([195.75.94.113]:56653 "EHLO e06smtp17.uk.ibm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S965410Ab3E2RM6 (ORCPT ); Wed, 29 May 2013 13:12:58 -0400 Date: Wed, 29 May 2013 19:12:49 +0200 From: Michael Holzheu To: Vivek Goyal Cc: Zhang Yanfei , "Eric W. Biederman" , HATAYAMA Daisuke , Jan Willeke , Martin Schwidefsky , Heiko Carstens , linux-kernel@vger.kernel.org, kexec@lists.infradead.org, Andrew Morton Subject: Re: [PATCH 0/2] kdump/mmap: Fix mmap of /proc/vmcore for s390 Message-ID: <20130529191249.19a235be@holzheu> In-Reply-To: <20130529162325.GD22146@redhat.com> References: <20130524143644.GD18218@redhat.com> <20130524170626.2ac06efe@holzheu> <20130524152849.GF18218@redhat.com> <87mwrkatgu.fsf@xmission.com> <51A006CF.90105@gmail.com> <87k3mnahkf.fsf@xmission.com> <51A076FE.3060604@gmail.com> <20130525145217.0549138a@holzheu> <20130528135500.GC7088@redhat.com> <20130529135144.7f95c4c0@holzheu> <20130529162325.GD22146@redhat.com> Organization: IBM X-Mailer: Claws Mail 3.8.0 (GTK+ 2.24.10; i686-pc-linux-gnu) Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit X-TM-AS-MML: No X-Content-Scanned: Fidelis XPS MAILER x-cbid: 13052917-0542-0000-0000-000005660AF9 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 3710 Lines: 94 On Wed, 29 May 2013 12:23:26 -0400 Vivek Goyal wrote: > On Wed, May 29, 2013 at 01:51:44PM +0200, Michael Holzheu wrote: > > On Tue, 28 May 2013 09:55:01 -0400 > > Vivek Goyal wrote: > > > > > On Sat, May 25, 2013 at 02:52:17PM +0200, Michael Holzheu wrote: > > > > [snip] > > > > > > Besides of the newmem mechanism, for completeness, we also > > > > implemented the oldmem ELF header mechansim in kexec. But this > > > > is disabled by default. > > > > > > > > See: "#ifdef WITH_ELF_HEADER" in > > > > kexec/arch/s390/crashdump-s390.c > > > > > > > > Currently no distribution uses the oldmem mechanism. > > > > > > Hi Michael, > > > > > > Mechanism to read from newmem is not there yet (your patches are > > > still being reviewed) and you mentioned that no distribution is > > > building kexec-tools with WITH_ELF_HEADER on s390. So how things > > > are currently working for kdump on s390? > > > > Hello Vivek, > > > > On s390, if we do not get the ELF header from the 1st kernel with > > "elfcorehdr=", we build the ELF header in the 2nd kernel. This is > > currently the default because WITH_ELF_HEADER is not defined for > > kexec tools. > > > > >>> START QUOTE > > > > [PATCH v3 1/3] kdump: Introduce ELF header in new memory feature > > > > Currently for s390 we create the ELF core header in the 2nd kernel > > with a small trick. We relocate the addresses in the ELF header in > > a way that for the /proc/vmcore code it seems to be in the 1st > > kernel (old) memory and the read_from_oldmem() returns the correct > > data. This allows the /proc/vmcore code to use the ELF header in > > the 2nd kernel. > > > > >>> END QUOTE > > > > For our current zfcpdump project (see "[PATCH 3/3]s390/kdump: Use > > vmcore for zfcpdump") we could no longer use this trick. Therefore > > we sent you the patches to get a clean interface for ELF header > > creation in the 2nd kernel. > > > > > > > > > > Therefore, if necessary, IMHO we can switch to the ELF header > > > > memory swap mechanism for s390 in the kernel. Of course we > > > > would then also have to adjust the (disabled) kexec code. > > > > > > So are you saying that s390 is ready to switch to mechanism of > > > creating ELF headers in first kernel by kexec-tools and new kernel > > > does not have to preare ELF headers? > > > > No, I meant that currently nobody is using the kexec tools ELF > > header creation in the 1st kernel on s390. We create the ELF header > > in the 2nd kernel (mainly because of our cpuplugd issue). > > > > Therefore, I think, we can safely change the ELF header creation in > > 2nd kernel to use your p_offset swap trick *and* we remove the swap > > code in the copy_oldmem_page() implementation (same kernel). > > Ok. Got it. So s390 can fix it in kernel without creating any backward > compatibility issues (given the fact that nobody sees to be using > kexec-tools to build headers). > > So please go ahead and fix it and that should solve your mmap() issue > too. Also please fix kexec-tools and that change will not be backward > compatible. Ok, I will do this. I think we should add this "swap in ELF header" patch to the "kdump: Allow ELF header creation in new kernel" patch series (on top of the mmap patch series). Because when I remove the swap code from copy_oldmem_page(), the old trick to access the ELF header in the first kernel memory will no longer work. Is that ok for you? Michael -- 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/