[PATCH v21 1/8] arm64: kdump: reserve memory for crash dump kernel

On Wed, Jul 06, 2016 at 03:11:45PM -0300, Thiago Jung Bauermann wrote:

Am Mittwoch, 06 Juli 2016, 16:52:19 schrieb AKASHI Takahiro:

quoted

On the startup of primary kernel, the memory region used by crash dump
kernel must be specified by "crashkernel=" kernel parameter.
reserve_crashkernel() will allocate and reserve the region for later use.

User space tools, like kexec-tools, will be able to find that region
marked as "Crash kernel" in /proc/iomem.

On powerpc, userspace tools get everything from the device tree (exposed to 
userspace in /proc/device-tree/), not /proc/iomem.

I started my kdump patches with arm (not arm64) implementation, and
so /proc/iomem is used for consistency. Since my kexec-tools (for arm64)
have to access /proc/iomem to identify usable memory regions on
*UEFI* systems anyway, I didn't think it was odd.

(Please note that UEFI won't expose memory regions information via
a device tree, but via ACPI table.)

In the case of the crashkernel reserved region, that information is in 
/chosen/linux,crashkernel-base and /chosen/linux,crashkernel-size.

Either way is fine I think. I'm just mentioning this for reference in case 
you want the ARM implementation to be closer to another arch which is also 
based on the device tree.

Adding those properties to a device tree is quite easy
(and it won't conflict with /proc/iomem), so I'd like 
to defer to arm64 maintainers.

Thanks,
-Takahiro AKASHI

-- 
[]'s
Thiago Jung Bauermann
IBM Linux Technology Center