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 1DD4CC10F14 for ; Tue, 15 Oct 2019 11:05:30 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id E13C52086A for ; Tue, 15 Oct 2019 11:05:29 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1731631AbfJOLF2 convert rfc822-to-8bit (ORCPT ); Tue, 15 Oct 2019 07:05:28 -0400 Received: from out02.mta.xmission.com ([166.70.13.232]:46141 "EHLO out02.mta.xmission.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726054AbfJOLF2 (ORCPT ); Tue, 15 Oct 2019 07:05:28 -0400 Received: from in01.mta.xmission.com ([166.70.13.51]) by out02.mta.xmission.com with esmtps (TLS1.2:ECDHE_RSA_AES_128_GCM_SHA256:128) (Exim 4.87) (envelope-from ) id 1iKKdl-0007dW-VC; Tue, 15 Oct 2019 05:05:21 -0600 Received: from ip68-227-160-95.om.om.cox.net ([68.227.160.95] helo=x220.xmission.com) by in01.mta.xmission.com with esmtpsa (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.87) (envelope-from ) id 1iKKdk-0007IJ-Jj; Tue, 15 Oct 2019 05:05:21 -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> <87zhi51ers.fsf@x220.int.ebiederm.org> <72edff0b-9778-2e83-224b-7fe70dfb8d73@redhat.com> Date: Tue, 15 Oct 2019 06:04:27 -0500 In-Reply-To: <72edff0b-9778-2e83-224b-7fe70dfb8d73@redhat.com> (lijiang's message of "Sun, 13 Oct 2019 17:36:28 +0800") Message-ID: <8736fu1d8k.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=1iKKdk-0007IJ-Jj;;;mid=<8736fu1d8k.fsf@x220.int.ebiederm.org>;;;hst=in01.mta.xmission.com;;;ip=68.227.160.95;;;frm=ebiederm@xmission.com;;;spf=neutral X-XM-AID: U2FsdGVkX19iVApUpJOYp2UXKbyUu9vVJ5ookFgRwWM= 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 in01.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? Reading through the code of crash_setup_memap_entries I see that what the code is doing now. The code is repeating the e820 memory map with the memory areas that were not reserved for the crash kernel removed. In which case what the code needs to be doing something like: cmd.type = E820_TYPE_RAM; flags = IORESOURCE_MEM; walk_iomem_res_desc(IORES_DESC_RESERVED, flags, 0, 1024*1024, &cmd, memmap_entry_callback); Depending on which bugs exist it might make sense to limit this to the low 640KiB. But finding something the kernel already recognizes as RAM should prevent most of those problems already. Barring bugs I admit it doesn't make sense to repeat the work that someone else has already done. This bit: /* Add e820 reserved ranges */ cmd.type = E820_TYPE_RESERVED; flags = IORESOURCE_MEM; walk_iomem_res_desc(IORES_DESC_RESERVED, flags, 0, -1, &cmd, memmap_entry_callback); Should probably start at 1MiB instead of 0. Just so we don't report the memory below 1MiB as unconditionally reserved. I don't properly understand the IORES_DESC_RESERVED flag, and how that differs from flags. So please test my suggestions to verify the code works as expected. Eric