Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752541AbbELFoV (ORCPT ); Tue, 12 May 2015 01:44:21 -0400 Received: from mx1.redhat.com ([209.132.183.28]:55185 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752064AbbELFoT (ORCPT ); Tue, 12 May 2015 01:44:19 -0400 Date: Tue, 12 May 2015 13:43:04 +0800 From: Dave Young To: AKASHI Takahiro Cc: Mark Rutland , Catalin Marinas , Will Deacon , "vgoyal@redhat.com" , "hbabus@us.ibm.com" , "linaro-kernel@lists.linaro.org" , "geoff@infradead.org" , "kexec@lists.infradead.org" , "linux-kernel@vger.kernel.org" , "broonie@kernel.org" , "david.griego@linaro.org" , "linux-arm-kernel@lists.infradead.org" , ard.biesheuvel@linaro.org Subject: Re: [v2 0/5] arm64: add kdump support Message-ID: <20150512054304.GA29874@localhost.localdomain> References: <1429861989-8417-1-git-send-email-takahiro.akashi@linaro.org> <20150424095312.GD29183@leverpostej> <55504956.9020007@linaro.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <55504956.9020007@linaro.org> User-Agent: Mutt/1.5.22.1-rc1 (2013-10-16) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2272 Lines: 54 On 05/11/15 at 03:16pm, AKASHI Takahiro wrote: > Hi > > Sorry for late response. I was on vacation. > > On 04/24/2015 06:53 PM, Mark Rutland wrote: > >Hi, > > > >On Fri, Apr 24, 2015 at 08:53:03AM +0100, AKASHI Takahiro wrote: > >>This patch set enables kdump (crash dump kernel) support on arm64 on top of > >>Geoff's kexec patchset. > >> > >>In this version, there are some arm64-specific usage/constraints: > >>1) "mem=" boot parameter must be specified on crash dump kernel > >> if the system starts on uefi. > > > >This sounds very painful. Why is this the case, and how do x86 and/or > >ia64 get around that? > > As Dave (Young) said, x86 uses "memmap=XX" kernel commandline parameters > to specify usable memory for crash dump kernel. Originally x86 use memmap=exactmap memmap=XX to specify each section of memories for 2nd kernel. But later because a lot of reserved type ranges need to be passed ie. for pci mmconfig, and kernel cmdline buffer is limited so kexec-tools later switch to passing these in x86 boot params as E820 memory ranges directly. > On my arm64 implementation, "linux,usable-memory" property is added > to device tree blob by kexec-tools for this purpose. > This is because, when I first implemented kdump on arm64, ppc is the only > architecture that supports kdump AND utilizes device trees. > Since kexec-tools as well as the kernel already has this framework, > I believed that device-tree approach was smarter than a commandline > parameter. > > However, uefi-based kernel ignores all the memory-related properties > in a device tree and so this "mem=" workaround was added. Kdump kernel reuses the memmap info getting from firmware during 1st kernel boot, I do not think the memmap info can be cooked for crash kernel usable memory. But it might be a better way to use a special fdt node for crash kernel memory even for UEFI.. Another way is introducing a similar memmap=, but maybe consider only system_ram type ranges. For other memory areas still use UEFI memmap. Thanks Dave -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/