From mboxrd@z Thu Jan 1 00:00:00 1970 Return-path: Date: Thu, 22 Oct 2015 13:15:48 +0800 From: Dave Young Subject: Re: [PATCH 13/16] arm64: kdump: add kdump support Message-ID: <20151022051548.GD11227@dhcp-129-115.nay.redhat.com> References: <20151022032534.GC11227@dhcp-129-115.nay.redhat.com> <5628662B.1020605@linaro.org> MIME-Version: 1.0 Content-Disposition: inline In-Reply-To: <5628662B.1020605@linaro.org> List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Sender: "kexec" Errors-To: kexec-bounces+dwmw2=infradead.org@lists.infradead.org To: AKASHI Takahiro Cc: Mark Rutland , AKASHI@infradead.org, Geoff Levand , Catalin Marinas , Will Deacon , marc.zyngier@arm.com, linux-arm-kernel@lists.infradead.org, kexec@lists.infradead.org, christoffer.dall@linaro.org On 10/22/15 at 01:29pm, AKASHI Takahiro wrote: > Hi Dave, > > Thank you for your comment. > > On 10/22/2015 12:25 PM, Dave Young wrote: > >Hi, AKASHI, > > > >On 10/19/15 at 11:38pm, Geoff Levand wrote: > >>From: AKASHI Takahiro > >> > >>On crash dump kernel, all the information about primary kernel's core > >>image is available in elf core header specified by "elfcorehdr=" boot > >>parameter. reserve_elfcorehdr() will set aside the region to avoid any > >>corruption by crash dump kernel. > >> > >>Crash dump kernel will access the system memory of primary kernel via > >>copy_oldmem_page(), which reads one page by ioremap'ing it since it does > >>not reside in linear mapping on crash dump kernel. > >>Please note that we should add "mem=X[MG]" boot parameter to limit the > >>memory size and avoid the following assertion at ioremap(): > >> if (WARN_ON(pfn_valid(__phys_to_pfn(phys_addr)))) > >> return NULL; > >>when accessing any pages beyond the usable memories of crash dump kernel. > > > >How does kexec-tools pass usable memory ranges to kernel? using dtb? > >Passing an extra mem=X sounds odd in the design. Kdump kernel should get > >usable ranges and hanle the limit better than depending on an extern kernel > >param. > > Well, regarding "depending on an external kernel param," > - this limitation ("mem=") is compatible with arm(32) implementation although > it is not clearly described in kernel's Documentation/kdump/kdump.txt. > - "elfcorehdr" kernel parameter is mandatory on x86 as well as on arm/arm64. > The parameter is explicitly generated and added by kexec-tools. > > Do I miss your point? Arm previously use atag_mem tag for memory kernel uses, with dtb, Booting.txt says: The boot loader must pass at a minimum the size and location of the system memory In arm64 booting.txt, it does mentions about dtb but without above sentence. So if you are using dtb to pass memory I think the extra mem= should be not necessary unless there's other limitations dtb can not been used. One thing I'm confused is mem= only pass the memory size, where does you pass the start addresses? What if there's multiple sections such as some reserved ranges 2nd kernel also need? Thanks Dave _______________________________________________ kexec mailing list kexec@lists.infradead.org http://lists.infradead.org/mailman/listinfo/kexec