From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S932173AbaIKUne (ORCPT ); Thu, 11 Sep 2014 16:43:34 -0400 Received: from cantor2.suse.de ([195.135.220.15]:43569 "EHLO mx2.suse.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S932149AbaIKUnd (ORCPT ); Thu, 11 Sep 2014 16:43:33 -0400 Date: Thu, 11 Sep 2014 22:43:30 +0200 From: Petr Tesarik To: Vivek Goyal Cc: kexec@lists.infradead.org, Eric Biederman , linux-kernel@vger.kernel.org Subject: Re: [PATCH] Put each per-cpu kdump ELF notes into a single page Message-ID: <20140911224330.0cec9b4c@hananiah.suse.cz> In-Reply-To: <20140911200110.GA24699@redhat.com> References: <20140905183314.23690175@hananiah.suse.cz> <20140911200110.GA24699@redhat.com> 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 On Thu, 11 Sep 2014 16:01:10 -0400 Vivek Goyal wrote: > On Fri, Sep 05, 2014 at 06:33:14PM +0200, Petr Tesarik wrote: > > On architectures that use percpu-vm, the percpu region is not guaranteed > > to be contiguous in physical space. > > Petr, > > Which are those arches? All except nommu. Actually, percpu-km will be used instead even on MMU if SMP is disabled, but since SMP is pretty standard now, I guess the vast majority of all kernels out there is affected. ;-) > > 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))); > > I think some of the changelog should show up here as comment in short > form. I don't think it is obvious that why we are using __alloc_percpu() > and why aligning to nearst higher power of 2 is needed here. Please also > mention here which arches run into issues. OK, I'll add it as a comment in the code. I'll see if I can make it short but still understandable. Thanks, Petr Tesarik > Thanks > Vivek > > > if (!crash_notes) { > > pr_warn("Kexec: Memory allocation for saving cpu register states failed\n"); > > return -ENOMEM; > > -- > > 1.8.4.5 > > > > _______________________________________________ > > kexec mailing list > > kexec@lists.infradead.org > > http://lists.infradead.org/mailman/listinfo/kexec > > _______________________________________________ > kexec mailing list > kexec@lists.infradead.org > http://lists.infradead.org/mailman/listinfo/kexec