From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753396Ab1HAUb6 (ORCPT ); Mon, 1 Aug 2011 16:31:58 -0400 Received: from mx1.redhat.com ([209.132.183.28]:42766 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753065Ab1HAUbx (ORCPT ); Mon, 1 Aug 2011 16:31:53 -0400 Date: Mon, 1 Aug 2011 16:31:43 -0400 From: Vivek Goyal To: Michael Holzheu Cc: ebiederm@xmission.com, mahesh@linux.vnet.ibm.com, hbabu@us.ibm.com, oomichi@mxs.nes.nec.co.jp, horms@verge.net.au, schwidefsky@de.ibm.com, heiko.carstens@de.ibm.com, kexec@lists.infradead.org, linux-kernel@vger.kernel.org, linux-s390@vger.kernel.org Subject: Re: [patch v2 02/10] kdump: Make kimage_load_crash_segment() weak Message-ID: <20110801203143.GH3805@redhat.com> References: <20110727125504.491183728@linux.vnet.ibm.com> <20110727125807.695225427@linux.vnet.ibm.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20110727125807.695225427@linux.vnet.ibm.com> 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 Wed, Jul 27, 2011 at 02:55:06PM +0200, Michael Holzheu wrote: > From: Michael Holzheu > > On s390 we do not create page tables at all for the crashkernel memory. > This requires a s390 specific version for kimage_load_crash_segment(). > Therefore this patch declares this function as "__weak". The s390 version is > very simple. It just copies the kexec segment to real memory without using > page tables: > > int kimage_load_crash_segment(struct kimage *image, > struct kexec_segment *segment) > { > return copy_from_user_real((void *) segment->mem, segment->buf, > segment->bufsz); > } > > There are two main advantages of not creating page tables for the > crashkernel memory: > > a) It saves memory. We have scenarios in mind, where crashkernel > memory can be very large and saving page table space is important. > b) We protect the crashkernel memory from being overwritten. > > Signed-off-by: Michael Holzheu > --- > kernel/kexec.c | 4 ++-- > 1 file changed, 2 insertions(+), 2 deletions(-) > > --- a/kernel/kexec.c > +++ b/kernel/kexec.c > @@ -842,8 +842,8 @@ out: > return result; > } > > -static int kimage_load_crash_segment(struct kimage *image, > - struct kexec_segment *segment) > +int __weak kimage_load_crash_segment(struct kimage *image, > + struct kexec_segment *segment) A comment here why we are making it weak should help in increasing the code readability. Thanks Vivek > { > /* For crash dumps kernels we simply copy the data from > * user space to it's destination.