numa: fix /proc/<pid>/numa_maps for THP

In gather_pte_stats() a THP pmd is cast into a pte, which is wrong
because the layouts may differ depending on the architecture.  On s390
this will lead to inaccurate numa_maps accounting in /proc because of
misguided pte_present() and pte_dirty() checks on the fake pte.

On other architectures pte_present() and pte_dirty() may work by chance,
but there may be an issue with direct-access (dax) mappings w/o
underlying struct pages when HAVE_PTE_SPECIAL is set and THP is
available.  In vm_normal_page() the fake pte will be checked with
pte_special() and because there is no "special" bit in a pmd, this will
always return false and the VM_PFNMAP | VM_MIXEDMAP checking will be
skipped.  On dax mappings w/o struct pages, an invalid struct page
pointer would then be returned that can crash the kernel.

This patch fixes the numa_maps THP handling by introducing new "_pmd"
variants of the can_gather_numa_stats() and vm_normal_page() functions.

Signed-off-by: Gerald Schaefer <[email protected]>
Cc: Naoya Horiguchi <[email protected]>
Cc: "Kirill A . Shutemov" <[email protected]>
Cc: Konstantin Khlebnikov <[email protected]>
Cc: Michal Hocko <[email protected]>
Cc: Vlastimil Babka <[email protected]>
Cc: Jerome Marchand <[email protected]>
Cc: Johannes Weiner <[email protected]>
Cc: Dave Hansen <[email protected]>
Cc: Mel Gorman <[email protected]>
Cc: Dan Williams <[email protected]>
Cc: Martin Schwidefsky <[email protected]>
Cc: Heiko Carstens <[email protected]>
Cc: Michael Holzheu <[email protected]>
Cc: <[email protected]>	[4.3+]
Signed-off-by: Andrew Morton <[email protected]>
Signed-off-by: Linus Torvalds <[email protected]>

1 files changed, 2 insertions, 0 deletions

diff --git a/include/linux/mm.h b/include/linux/mm.h
index 79b6c18d0a38..864d7221de84 100644
--- a/include/linux/mm.h
+++ b/include/linux/mm.h
@@ -1140,6 +1140,8 @@ struct zap_details {
 
 struct page *vm_normal_page(struct vm_area_struct *vma, unsigned long addr,
 		pte_t pte);
+struct page *vm_normal_page_pmd(struct vm_area_struct *vma, unsigned long addr,
+				pmd_t pmd);
 
 int zap_vma_ptes(struct vm_area_struct *vma, unsigned long address,
 		unsigned long size);