From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-6.8 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 797E9ECE588 for ; Tue, 15 Oct 2019 11:12:19 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 4DD3D20873 for ; Tue, 15 Oct 2019 11:12:19 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1731742AbfJOLMS convert rfc822-to-8bit (ORCPT ); Tue, 15 Oct 2019 07:12:18 -0400 Received: from out03.mta.xmission.com ([166.70.13.233]:42398 "EHLO out03.mta.xmission.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1728769AbfJOLMR (ORCPT ); Tue, 15 Oct 2019 07:12:17 -0400 Received: from in02.mta.xmission.com ([166.70.13.52]) by out03.mta.xmission.com with esmtps (TLS1.2:ECDHE_RSA_AES_128_GCM_SHA256:128) (Exim 4.87) (envelope-from ) id 1iKKkR-0004nD-5y; Tue, 15 Oct 2019 05:12:15 -0600 Received: from ip68-227-160-95.om.om.cox.net ([68.227.160.95] helo=x220.xmission.com) by in02.mta.xmission.com with esmtpsa (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.87) (envelope-from ) id 1iKKkQ-0005CK-BC; Tue, 15 Oct 2019 05:12:15 -0600 From: ebiederm@xmission.com (Eric W. Biederman) To: lijiang Cc: Dave Young , linux-kernel@vger.kernel.org, tglx@linutronix.de, mingo@redhat.com, bp@alien8.de, hpa@zytor.com, x86@kernel.org, bhe@redhat.com, jgross@suse.com, dhowells@redhat.com, Thomas.Lendacky@amd.com, vgoyal@redhat.com, kexec@lists.infradead.org References: <20191012022140.19003-1-lijiang@redhat.com> <20191012022140.19003-4-lijiang@redhat.com> <87d0f22oi5.fsf@x220.int.ebiederm.org> <20191012121625.GA11587@dhcp-128-65.nay.redhat.com> Date: Tue, 15 Oct 2019 06:11:21 -0500 In-Reply-To: (lijiang's message of "Mon, 14 Oct 2019 18:02:22 +0800") Message-ID: <87tv8az2jq.fsf@x220.int.ebiederm.org> User-Agent: Gnus/5.13 (Gnus v5.13) Emacs/26.1 (gnu/linux) MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: 8BIT X-XM-SPF: eid=1iKKkQ-0005CK-BC;;;mid=<87tv8az2jq.fsf@x220.int.ebiederm.org>;;;hst=in02.mta.xmission.com;;;ip=68.227.160.95;;;frm=ebiederm@xmission.com;;;spf=neutral X-XM-AID: U2FsdGVkX1/CQX+QOBFNW++gFp6mHXP7BzIXPyWEAgA= X-SA-Exim-Connect-IP: 68.227.160.95 X-SA-Exim-Mail-From: ebiederm@xmission.com Subject: Re: [PATCH 3/3 v3] x86/kdump: clean up all the code related to the backup region X-SA-Exim-Version: 4.2.1 (built Thu, 05 May 2016 13:38:54 -0600) X-SA-Exim-Scanned: Yes (on in02.mta.xmission.com) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org lijiang writes: > 在 2019年10月12日 20:16, Dave Young 写道: >> Hi Eric, >> >> On 10/12/19 at 06:26am, Eric W. Biederman wrote: >>> Lianbo Jiang writes: >>> >>>> When the crashkernel kernel command line option is specified, the >>>> low 1MiB memory will always be reserved, which makes that the memory >>>> allocated later won't fall into the low 1MiB area, thereby, it's not >>>> necessary to create a backup region and also no need to copy the first >>>> 640k content to a backup region. >>>> >>>> Currently, the code related to the backup region can be safely removed, >>>> so lets clean up. >>>> >>>> Signed-off-by: Lianbo Jiang >>>> --- >>> >>>> diff --git a/arch/x86/kernel/crash.c b/arch/x86/kernel/crash.c >>>> index eb651fbde92a..cc5774fc84c0 100644 >>>> --- a/arch/x86/kernel/crash.c >>>> +++ b/arch/x86/kernel/crash.c >>>> @@ -173,8 +173,6 @@ void native_machine_crash_shutdown(struct pt_regs *regs) >>>> >>>> #ifdef CONFIG_KEXEC_FILE >>>> >>>> -static unsigned long crash_zero_bytes; >>>> - >>>> static int get_nr_ram_ranges_callback(struct resource *res, void *arg) >>>> { >>>> unsigned int *nr_ranges = arg; >>>> @@ -234,9 +232,15 @@ static int prepare_elf64_ram_headers_callback(struct resource *res, void *arg) >>>> { >>>> struct crash_mem *cmem = arg; >>>> >>>> - cmem->ranges[cmem->nr_ranges].start = res->start; >>>> - cmem->ranges[cmem->nr_ranges].end = res->end; >>>> - cmem->nr_ranges++; >>>> + if (res->start >= SZ_1M) { >>>> + cmem->ranges[cmem->nr_ranges].start = res->start; >>>> + cmem->ranges[cmem->nr_ranges].end = res->end; >>>> + cmem->nr_ranges++; >>>> + } else if (res->end > SZ_1M) { >>>> + cmem->ranges[cmem->nr_ranges].start = SZ_1M; >>>> + cmem->ranges[cmem->nr_ranges].end = res->end; >>>> + cmem->nr_ranges++; >>>> + } >>> >>> What is going on with this chunk? I can guess but this needs a clear >>> comment. >> >> Indeed it needs some code comment, this is based on some offline >> discussion. cat /proc/vmcore will give a warning because ioremap is >> mapping the system ram. >> >> We pass the first 1M to kdump kernel in e820 as system ram so that 2nd >> kernel can use the low 1M memory because for example the trampoline >> code. >> > Thank you, Eric and Dave. I will add the code comment as below if it would be OK. > > @@ -234,9 +232,20 @@ static int prepare_elf64_ram_headers_callback(struct resource *res, void *arg) > { > struct crash_mem *cmem = arg; > > - cmem->ranges[cmem->nr_ranges].start = res->start; > - cmem->ranges[cmem->nr_ranges].end = res->end; > - cmem->nr_ranges++; > + /* > + * Currently, pass the low 1MiB range to kdump kernel in e820 > + * as system ram so that kdump kernel can also use the low 1MiB > + * memory due to the real mode trampoline code. > + * And later, the low 1MiB range will be exclued from elf header, > + * which will avoid remapping the 1MiB system ram when dumping > + * vmcore. > + */ > + if (res->start >= SZ_1M) { > + cmem->ranges[cmem->nr_ranges].start = res->start; > + cmem->ranges[cmem->nr_ranges].end = res->end; > + cmem->nr_ranges++; > + } else if (res->end > SZ_1M) { > + cmem->ranges[cmem->nr_ranges].start = SZ_1M; > + cmem->ranges[cmem->nr_ranges].end = res->end; > + cmem->nr_ranges++; > + } > > return 0; > } I just read through the appropriate section of crash.c and the way things are structured doing this work in prepare_elf64_ram_headers_callback is wrong. This can be done in a simpler manner in elf_header_exclude_ranges. Something like: /* The low 1MiB is always reserved */ ret = crash_exclude_mem_range(cmem, 0, 1024*1024); if (ret) return ret; Eric