[PATCH] numa: fix /proc/<pid>/numa_maps for hugetlbfs on s390

[Michael Holzheu]

When working with hugetlbfs ptes (which are actually pmds) is not
valid to directly use pte functions like pte_present() because the
hardware bit layout of pmds and ptes can be different. This is the
case on s390. Therefore we have to convert the hugetlbfs ptes first
into a valid pte encoding with huge_ptep_get().

Currently the /proc/<pid>/numa_maps code uses hugetlbfs ptes without
huge_ptep_get(). On s390 this leads to the following two problems:

1) The pte_present() function returns false (instead of true) for
   PROT_NONE hugetlb ptes. Therefore PROT_NONE vmas are missing
   completely in the "numa_maps" output.

2) The pte_dirty() function always returns false for all hugetlb ptes.
   Therefore these pages are reported as "mapped=xxx" instead of
   "dirty=xxx".

Therefore use huge_ptep_get() to correctly convert the hugetlb ptes.

Reviewed-by: Gerald Schaefer <gerald.schaefer@xxxxxxxxxx>
Signed-off-by: Michael Holzheu <holzheu@xxxxxxxxxxxxxxxxxx>
---
 fs/proc/task_mmu.c | 7 ++++---
 1 file changed, 4 insertions(+), 3 deletions(-)

diff --git a/fs/proc/task_mmu.c b/fs/proc/task_mmu.c
index 85d16c6..4a0c31f 100644
--- a/fs/proc/task_mmu.c
+++ b/fs/proc/task_mmu.c
@@ -1552,18 +1552,19 @@ static int gather_pte_stats(pmd_t *pmd, unsigned long addr,
 static int gather_hugetlb_stats(pte_t *pte, unsigned long hmask,
 		unsigned long addr, unsigned long end, struct mm_walk *walk)
 {
+	pte_t huge_pte = huge_ptep_get(pte);
 	struct numa_maps *md;
 	struct page *page;
 
-	if (!pte_present(*pte))
+	if (!pte_present(huge_pte))
 		return 0;
 
-	page = pte_page(*pte);
+	page = pte_page(huge_pte);
 	if (!page)
 		return 0;
 
 	md = walk->private;
-	gather_stats(page, md, pte_dirty(*pte), 1);
+	gather_stats(page, md, pte_dirty(huge_pte), 1);
 	return 0;
 }
 
-- 
2.3.9