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Subject: Re: [PATCH] powerpc/crashdump : fix page frame number check in
 copy_oldmem_page
From: Michael Ellerman <mpe@ellerman.id.au>
To: Laurent Dufour <ldufour@linux.vnet.ibm.com>
Date: Tue, 25 Feb 2014 12:47:02 +1100
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Cc: Paul Mackerras <paulus@samba.org>, linuxppc-dev@lists.ozlabs.org
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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.

cheers