Subject: Re: [PATCH] powerpc/crashdump : fix page frame number check in copy_oldmem_page

From: Laurent Dufour <[email-masked]>
Date: Wed, 26 Feb 2014 15:04:37 +0100

On 25/02/2014 02:47, Michael Ellerman wrote:
> On Mon, 2014-02-24 at 17:30 +0100, Laurent Dufour wrote:
>> In copy_oldmem_page, the current check using max_pfn and min_low_pfn to
>> decide if the page is backed or not, is not valid when the memory layout is
>> not continuous.
>>
>> This happens when running as a QEMU/KVM guest, where RTAS is mapped higher
>> in the memory. In that case max_pfn points to the end of RTAS, and a hole
>> between the end of the kdump kernel and RTAS is not backed by PTEs. As a
>> consequence, the kdump kernel is crashing in copy_oldmem_page when accessing
>> in a direct way the pages in that hole.
>>
>> This fix relies on the memblock's service memblock_is_region_memory to
>> check if the read page is part or not of the directly accessible memory.
> 
> Hi Laurent,
> 
> This looks good to me, assuming you've tested it on a PowerVM system as well as
> under KVM.

Hi Michael,

Yes I tested it on PowerVM (BE), KVM (BE) and Qemu TCG (BE).

Cheers,
Laurent.