Patch "numa: fix /proc/<pid>/numa_maps for hugetlbfs on s390" has been added to the 4.4-stable tree

This is a note to let you know that I've just added the patch titled

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

to the 4.4-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
numa-fix-proc-pid-numa_maps-for-hugetlbfs-on-s390.patch
and it can be found in the queue-4.4 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree, please let <[email protected]> know about it.

From: Michael Holzheu <[email protected]>
Date: Tue, 2 Feb 2016 16:57:26 -0800
Subject: numa: fix /proc/<pid>/numa_maps for hugetlbfs on s390

From: Michael Holzheu <[email protected]>

commit 5c2ff95e41c9290d16556cd02e35b25d81be8fe0 upstream.

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.

---
 fs/proc/task_mmu.c |    7 ++++---
 1 file changed, 4 insertions(+), 3 deletions(-)

@@ -1473,18 +1473,19 @@ static int gather_pte_stats(pmd_t *pmd,
 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;
 }
 

Patches currently in stable-queue which might be from [email protected] are

queue-4.4/numa-fix-proc-pid-numa_maps-for-hugetlbfs-on-s390.patch