[PATCH 16/19] arm64: kdump: add kdump support

Hi!

On 15/01/16 19:18, Geoff Levand wrote:

From: AKASHI Takahiro <redacted>

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.

We also need our own elfcorehdr_read() here since the weak definition of
elfcorehdr_read() utilizes copy_oldmem_page() and will hit the assertion
above on arm64.

How does this work for a different-endian crash kernel?

It looks like fs/proc/vmcore.c:parse_crash_elf64_headers() does some
validation on the elf-headers that doesn't look like it will work if
elfcorehdr:endian != kernel:endian.

Is it worth preventing this corner case by getting kexec-tools to
prevent linux with a different endianness being loaded as a kdump kernel?


Thanks,

James