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=-8.3 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS, USER_AGENT_SANE_1 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 50218C4360C for ; Sun, 13 Oct 2019 09:36:58 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 29FAF20679 for ; Sun, 13 Oct 2019 09:36:58 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1728855AbfJMJgq (ORCPT ); Sun, 13 Oct 2019 05:36:46 -0400 Received: from mx1.redhat.com ([209.132.183.28]:39798 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1728662AbfJMJgq (ORCPT ); Sun, 13 Oct 2019 05:36:46 -0400 Received: from smtp.corp.redhat.com (int-mx05.intmail.prod.int.phx2.redhat.com [10.5.11.15]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mx1.redhat.com (Postfix) with ESMTPS id BA2B537E80; Sun, 13 Oct 2019 09:36:45 +0000 (UTC) Received: from localhost.localdomain (ovpn-12-16.pek2.redhat.com [10.72.12.16]) by smtp.corp.redhat.com (Postfix) with ESMTPS id A30BB5D6A3; Sun, 13 Oct 2019 09:36:34 +0000 (UTC) Subject: Re: [PATCH 3/3 v3] x86/kdump: clean up all the code related to the backup region To: "Eric W. Biederman" , Dave Young Cc: 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> <87zhi51ers.fsf@x220.int.ebiederm.org> From: lijiang Message-ID: <72edff0b-9778-2e83-224b-7fe70dfb8d73@redhat.com> Date: Sun, 13 Oct 2019 17:36:28 +0800 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:52.0) Gecko/20100101 Thunderbird/52.9.1 MIME-Version: 1.0 In-Reply-To: <87zhi51ers.fsf@x220.int.ebiederm.org> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 8bit X-Scanned-By: MIMEDefang 2.79 on 10.5.11.15 X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.5.16 (mx1.redhat.com [10.5.110.29]); Sun, 13 Oct 2019 09:36:45 +0000 (UTC) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 在 2019年10月13日 11:54, Eric W. Biederman 写道: > Dave Young writes: > >> 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. >> >>> >>>> >>>> return 0; >>>> } >>> >>>> @@ -356,9 +337,12 @@ int crash_setup_memmap_entries(struct kimage *image, struct boot_params *params) >>>> memset(&cmd, 0, sizeof(struct crash_memmap_data)); >>>> cmd.params = params; >>>> >>>> - /* Add first 640K segment */ >>>> - ei.addr = image->arch.backup_src_start; >>>> - ei.size = image->arch.backup_src_sz; >>>> + /* >>>> + * Add the low memory range[0x1000, SZ_1M], skip >>>> + * the first zero page. >>>> + */ >>>> + ei.addr = PAGE_SIZE; >>>> + ei.size = SZ_1M - PAGE_SIZE; >>>> ei.type = E820_TYPE_RAM; >>>> add_e820_entry(params, &ei); >>> >>> Likewise here. Why do we need a special case? >>> Why the magic with PAGE_SIZE? >> >> Good catch, the zero page part is useless, I think no other special >> reason, just assumed zero page is not usable, but it should be ok to >> remove the special handling, just pass 0 - 1M is good enough. > > But if we have stopped special casing the low 1M. Why do we need a > special case here at all? > Here, need to pass the low memory range to kdump kernel, which will guarantee the availability of low memory in kdump kernel, otherwise, kdump kernel won't use the low memory region. > If you need the special case it is almost certainly wrong to say you > have ram above 640KiB and below 1MiB. That is the legacy ROM and video > MMIO area. > > There is a reason the original code said 640KiB. > Do you mean that the 640k region is good enough here instead of 1MiB? Thanks. Lianbo > Eric >