FAILED: patch "[PATCH] s390/mm: fix CMMA vs KSM vs others" failed to apply to 4.9-stable tree

The patch below does not apply to the 4.9-stable tree.
If someone wants it applied there, or to any other stable or longterm tree, then please email the backport, including the original git commit id to <[email protected]>.

thanks,

greg k-h

------------------ original commit in Linus's tree ------------------

From: Christian Borntraeger <[email protected]>
Date: Sun, 9 Apr 2017 22:09:38 +0200
Subject: [PATCH] s390/mm: fix CMMA vs KSM vs others

On heavy paging with KSM I see guest data corruption. Turns out that KSM will add pages to its tree, where the mapping return true for pte_unused (or might become as such later). KSM will unmap such pages and reinstantiate with different attributes (e.g. write protected or special, e.g. in replace_page or write_protect_page)). This uncovered a bug in our pagetable handling: We must remove the unused flag as soon as an entry becomes present again.

index 93e37b12e882..ecec682bb516 100644
@@ -1051,6 +1051,8 @@ static inline void set_pte_at(struct mm_struct *mm, unsigned long addr,
 {
 	if (!MACHINE_HAS_NX)
 		pte_val(entry) &= ~_PAGE_NOEXEC;
+	if (pte_present(entry))
+		pte_val(entry) &= ~_PAGE_UNUSED;
 	if (mm_has_pgste(mm))
 		ptep_set_pte_at(mm, addr, ptep, entry);
 	else