commit a96dfddbcc upstream.
Reading a sysfs "memoryN/valid_zones" file leads to the following oops
when the first page of a range is not backed by struct page.
show_valid_zones() assumes that 'start_pfn' is always valid for
page_zone().
BUG: unable to handle kernel paging request at ffffea017a000000
IP: show_valid_zones+0x6f/0x160
This issue may happen on x86-64 systems with 64GiB or more memory since
their memory block size is bumped up to 2GiB. [1] An example of such
systems is desribed below. 0x3240000000 is only aligned by 1GiB and
this memory block starts from 0x3200000000, which is not backed by
struct page.
BIOS-e820: [mem 0x0000003240000000-0x000000603fffffff] usable
Since test_pages_in_a_zone() already checks holes, fix this issue by
extending this function to return 'valid_start' and 'valid_end' for a
given range. show_valid_zones() then proceeds with the valid range.
[1] 'Commit bdee237c03 ("x86: mm: Use 2GB memory block size on
large-memory x86-64 systems")'
Link: http://lkml.kernel.org/r/20170127222149.30893-3-toshi.kani@hpe.com
Signed-off-by: Toshi Kani <toshi.kani@hpe.com>
Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Cc: Zhang Zhen <zhenzhang.zhang@huawei.com>
Cc: Reza Arbab <arbab@linux.vnet.ibm.com>
Cc: David Rientjes <rientjes@google.com>
Cc: Dan Williams <dan.j.williams@intel.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
6cb0497aec