From mboxrd@z Thu Jan 1 00:00:00 1970 Return-path: Date: Fri, 23 Oct 2015 17:50:59 +0800 From: Dave Young Subject: Re: [PATCH 13/16] arm64: kdump: add kdump support Message-ID: <20151023095059.GH11227@dhcp-129-115.nay.redhat.com> References: <20151022032534.GC11227@dhcp-129-115.nay.redhat.com> <5628662B.1020605@linaro.org> <20151022051548.GD11227@dhcp-129-115.nay.redhat.com> <5628B2FA.80209@linaro.org> MIME-Version: 1.0 Content-Disposition: inline In-Reply-To: <5628B2FA.80209@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, ard.biesheuvel@linaro.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 06:57pm, AKASHI Takahiro wrote: > (added Ard to Cc.) > > On 10/22/2015 02:15 PM, Dave Young wrote: > >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. > > I would expect comments from arm64 maintainers here. > > In my old implementation, I added "usablemem" attributes, along with "reg," to > "memory" nodes in dtb to specify the usable memory region on crash dump kernel. > > But I removed this feature partly because, on uefi system, uefi might pass > no memory information in dtb. If this is the case there must be somewhere else one can pass memory infomation to kernel, the booting.txt should be updated? kexec as a boot loader need use same method as the 1st kernel boot loader. > > >One thing I'm confused is mem= only pass the memory size, where does you pass > >the start addresses? > > In the current arm64 implementation, any regions below the start address will > be ignored as system ram. > > >What if there's multiple sections such as some reserved > >ranges 2nd kernel also need? > > My patch utilizes only a single contiguous region of memory as system ram. > One exception that I notice is uefi's runtime data. They will be ioremap'ed separately. > > Please let me know if there is any other case that should be supported. For example the elf headers range, you reserved them in kdump kernel code, but kexec-tools can do that early if it can provides all memory info to 2nd kernel. Ditto for mark all the memory ranges 1st kernel used as reserved. Thanks Dave _______________________________________________ kexec mailing list kexec@lists.infradead.org http://lists.infradead.org/mailman/listinfo/kexec