[PATCH 13/16] arm64: kdump: add kdump support
dyoung at redhat.com
Fri Oct 23 02:50:59 PDT 2015
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 <takahiro.akashi at linaro.org>
> >>>>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
> >>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.
More information about the kexec