Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1759100AbdCVMRQ (ORCPT ); Wed, 22 Mar 2017 08:17:16 -0400 Received: from mx0a-001b2d01.pphosted.com ([148.163.156.1]:53302 "EHLO mx0a-001b2d01.pphosted.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1758838AbdCVMRG (ORCPT ); Wed, 22 Mar 2017 08:17:06 -0400 Subject: Re: [PATCH v3 1/3] kexec: Move vmcoreinfo out of the kernel's .bss section To: xlpang@redhat.com, Dave Young , "Eric W. Biederman" References: <1489989033-1179-1-git-send-email-xlpang@redhat.com> <87pohbz4lo.fsf@xmission.com> <20170322025536.GA4424@dhcp-128-65.nay.redhat.com> <87pohaxam1.fsf@xmission.com> <20170322043004.GB4424@dhcp-128-65.nay.redhat.com> <58D24543.5020700@redhat.com> Cc: Baoquan He , Atsushi Kumagai , Petr Tesarik , linux-kernel@vger.kernel.org, akpm@linux-foundation.org, holzheu@linux.vnet.ibm.com, kexec@lists.infradead.org From: Hari Bathini Date: Wed, 22 Mar 2017 17:45:28 +0530 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:45.0) Gecko/20100101 Thunderbird/45.7.0 MIME-Version: 1.0 In-Reply-To: <58D24543.5020700@redhat.com> Content-Type: text/plain; charset=windows-1252; format=flowed Content-Transfer-Encoding: 7bit X-TM-AS-MML: disable x-cbid: 17032212-1617-0000-0000-000001B9A7A0 X-IBM-AV-DETECTION: SAVI=unused REMOTE=unused XFE=unused x-cbparentid: 17032212-1618-0000-0000-000047F65449 Message-Id: <30b07524-0558-7edb-3b0f-ba5e4976ffb7@linux.vnet.ibm.com> X-Proofpoint-Virus-Version: vendor=fsecure engine=2.50.10432:,, definitions=2017-03-22_10:,, signatures=0 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 spamscore=0 suspectscore=0 malwarescore=0 phishscore=0 adultscore=0 bulkscore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.0.1-1702020001 definitions=main-1703220107 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2022 Lines: 46 Hi Xunlei, On Wednesday 22 March 2017 03:04 PM, Xunlei Pang wrote: > On 03/22/2017 at 12:30 PM, Dave Young wrote: >> On 03/21/17 at 10:18pm, Eric W. Biederman wrote: >>> Dave Young writes: >>> >>>> On 03/20/17 at 10:33pm, Eric W. Biederman wrote: >>>>> Xunlei Pang writes: >>>>> >>>>>> As Eric said, >>>>>> "what we need to do is move the variable vmcoreinfo_note out >>>>>> of the kernel's .bss section. And modify the code to regenerate >>>>>> and keep this information in something like the control page. >>>>>> >>>>>> Definitely something like this needs a page all to itself, and ideally >>>>>> far away from any other kernel data structures. I clearly was not >>>>>> watching closely the data someone decided to keep this silly thing >>>>>> in the kernel's .bss section." >>>>>> >>>>>> This patch allocates extra pages for these vmcoreinfo_XXX variables, >>>>>> one advantage is that it enhances some safety of vmcoreinfo, because >>>>>> vmcoreinfo now is kept far away from other kernel data structures. >>>>> Can you preceed this patch with a patch that removes CRASHTIME from >>>>> vmcoreinfo? If someone actually cares we can add a separate note that holds >>>>> a 64bit crashtime in the per cpu notes. >>>> I think makedumpfile is using it, but I also vote to remove the >>>> CRASHTIME. It is better not to do this while crashing and a makedumpfile >>>> userspace patch is needed to drop the use of it. >>>> > By moving the CRASHTIME info to the cpu note of crashed cpu may be a good > way. In kdump kernel, notes of vmcore elfhdr will be merged into one big note > section, I don't know how makedumpfile or crash handle the big note section? > If they process the note in some order, breakage will definitely happen... > > There is also a fadump may be affected. > Would like to keep a tab of such change as fadump builds cpu notes differently and such change may have an impact on it considering it depends on the same tools - crash, makedumpfile.. Thanks Hari