From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1756077AbaIKTht (ORCPT ); Thu, 11 Sep 2014 15:37:49 -0400 Received: from cantor2.suse.de ([195.135.220.15]:42753 "EHLO mx2.suse.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752886AbaIKThs (ORCPT ); Thu, 11 Sep 2014 15:37:48 -0400 Date: Thu, 11 Sep 2014 21:37:44 +0200 From: Petr Tesarik To: Eric Biederman Cc: Vivek Goyal , kexec@lists.infradead.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH] Put each per-cpu kdump ELF notes into a single page Message-ID: <20140911213744.42735c3c@hananiah.suse.cz> In-Reply-To: <20140905183314.23690175@hananiah.suse.cz> References: <20140905183314.23690175@hananiah.suse.cz> Organization: SUSE Linux, s.r.o. X-Mailer: Claws Mail 3.9.2 (GTK+ 2.24.22; x86_64-suse-linux-gnu) Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Hi all, is anything wrong with the patch below? Are there questions? I thought this would be an easy one-line bugfix... Regards, Petr Tesarik On Fri, 5 Sep 2014 18:33:14 +0200 Petr Tesarik wrote: > On architectures that use percpu-vm, the percpu region is not guaranteed > to be contiguous in physical space. However, fs/proc/vmcore.c expects > all ELF notes to be contiguous. If the ELF note happens to occupy > two non-adjacent physical pages, part of the note may be read from an > incorrect memory location by the kdump kernel, resulting in failure to > initialize /proc/vmcore (if the content of the following physical page, > incorrectly interpreted as an ELF note specifies a large number), wrong > register values or other apparent random memory corruption. > > There is currently no mechanism to pass the virtual-to-physical mapping > of the percpu allocation to the kdump kernel. So, instead, I'm changing > the alignment of the ELF note buffer. Since sizeof(note_buf_t) is less > than PAGE_SIZE, aligning the buffer to the nearest higher power of 2 > is enough to make sure that the buffer cannot cross a page boundary, > effectively ensuring that the whole buffer is contiguous in physical > space. > > Signed-off-by: Petr Tesarik > --- > kernel/kexec.c | 3 ++- > 1 file changed, 2 insertions(+), 1 deletion(-) > > diff --git a/kernel/kexec.c b/kernel/kexec.c > index 2bee072..cdab59d 100644 > --- a/kernel/kexec.c > +++ b/kernel/kexec.c > @@ -1610,7 +1610,8 @@ void crash_save_cpu(struct pt_regs *regs, int cpu) > static int __init crash_notes_memory_init(void) > { > /* Allocate memory for saving cpu registers. */ > - crash_notes = alloc_percpu(note_buf_t); > + crash_notes = __alloc_percpu(sizeof(note_buf_t), > + roundup_pow_of_two(sizeof(note_buf_t))); > if (!crash_notes) { > pr_warn("Kexec: Memory allocation for saving cpu register states failed\n"); > return -ENOMEM;