fs/proc/page.c: allow inspection of last section and fix end detection

If max_pfn does not fall onto a section boundary, it is possible to
inspect PFNs up to max_pfn, and PFNs above max_pfn, however, max_pfn
itself can't be inspected.  We can have a valid (and online) memmap at and
above max_pfn if max_pfn is not aligned to a section boundary.  The whole
early section has a memmap and is marked online.  Being able to inspect
the state of these PFNs is valuable for debugging, especially because
max_pfn can change on memory hotplug and expose these memmaps.

Also, querying page flags via "./page-types -r -a 0x144001,"
(tools/vm/page-types.c) inside a x86-64 guest with 4160MB under QEMU
results in an (almost) endless loop in user space, because the end is not
detected properly when starting after max_pfn.

Instead, let's allow to inspect all pages in the highest section and
return 0 directly if we try to access pages above that section.

While at it, check the count before adjusting it, to avoid masking user
errors.

Link: http://lkml.kernel.org/r/[email protected]
Signed-off-by: David Hildenbrand <[email protected]>
Cc: Alexey Dobriyan <[email protected]>
Cc: Oscar Salvador <[email protected]>
Cc: Michal Hocko <[email protected]>
Cc: Stephen Rothwell <[email protected]>
Cc: Bob Picco <[email protected]>
Cc: Daniel Jordan <[email protected]>
Cc: Dan Williams <[email protected]>
Cc: Michal Hocko <[email protected]>
Cc: Naoya Horiguchi <[email protected]>
Cc: Pavel Tatashin <[email protected]>
Cc: Steven Sistare <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>
Signed-off-by: Linus Torvalds <[email protected]>

0 files changed, 0 insertions, 0 deletions