powerpc/crashdump : Fix page frame number check in copy_oldmem_page
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. Signed-off-by: NLaurent Dufour <ldufour@linux.vnet.ibm.com> Tested-by: NMahesh Salgaonkar <mahesh@linux.vnet.ibm.com> CC: <stable@vger.kernel.org> Signed-off-by: NBenjamin Herrenschmidt <benh@kernel.crashing.org>
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