On 25/02/2014 02:47, Michael Ellerman wrote:

On Mon, 2014-02-24 at 17:30 +0100, Laurent Dufour wrote:

quoted

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.