From mboxrd@z Thu Jan 1 00:00:00 1970 Return-path: Received: from mail-pa0-x235.google.com ([2607:f8b0:400e:c03::235]) by bombadil.infradead.org with esmtps (Exim 4.80.1 #2 (Red Hat Linux)) id 1ZpCd0-00038a-Nn for kexec@lists.infradead.org; Thu, 22 Oct 2015 09:57:48 +0000 Received: by padhk11 with SMTP id hk11so83139540pad.1 for ; Thu, 22 Oct 2015 02:57:26 -0700 (PDT) Subject: Re: [PATCH 13/16] arm64: kdump: add kdump support References: <20151022032534.GC11227@dhcp-129-115.nay.redhat.com> <5628662B.1020605@linaro.org> <20151022051548.GD11227@dhcp-129-115.nay.redhat.com> From: AKASHI Takahiro Message-ID: <5628B2FA.80209@linaro.org> Date: Thu, 22 Oct 2015 18:57:14 +0900 MIME-Version: 1.0 In-Reply-To: <20151022051548.GD11227@dhcp-129-115.nay.redhat.com> List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Content-Transfer-Encoding: 7bit Content-Type: text/plain; charset="us-ascii"; Format="flowed" Sender: "kexec" Errors-To: kexec-bounces+dwmw2=infradead.org@lists.infradead.org To: Dave Young 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 (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. > 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. Thanks, -Takahiro AKASHI > Thanks > Dave > _______________________________________________ kexec mailing list kexec@lists.infradead.org http://lists.infradead.org/mailman/listinfo/kexec