Re: [PATCH 1/5] arm64: kdump: reserve memory for crash dump kernel

From: Pratyush Anand
Date: Thu Apr 09 2015 - 09:11:11 EST

Hi Takahiro,

On Thursday 26 March 2015 01:58 PM, AKASHI Takahiro wrote:
Crash dump kernel will access memory regions in system kernel via
copy_oldmem_page(), which reads a page with ioremap'ing it assuming that
such pages are not part of main memory of crash dump kernel.
This is true under non-UEFI environment because kexec-tools modifies
a device tree adding "usablemem" attributes to memory sections.
Under UEFI, however, this is not true because UEFI remove memory sections
in a device tree and export all the memory regions, even though they belong
to system kernel.

So we should add "mem=X[MG]" boot parameter to limit the meory size and
avoid hitting the following assertion in ioremap():
if (WARN_ON(pfn_valid(__phys_to_pfn(phys_addr))))
return NULL;

Well I am using your updated kexec-tool which has support of automatic addition of "mem=" parameter. I found that this warning is still appearing and therefore another error about "Kdump: vmcore not initialized".

Memory address for which ioremap failed was almost at the top of crash_reserved_mem. So I modified kexec-tool [1] to accept user specific mem= parameter with a value lesser than physical location which was being remapped, however still the warning was there.

Further I noticed that there is no reserved memblock with nonzero memblock_region->size when early_mem -> memblock_enforce_memory_limit is called. Therefore this mem= param is not limiting memory location in my case.

I was just wondering, why do not we use ioremap_cache instead of ioremap in copy_oldmem_page?


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