mm: rmap: use correct helper when poisoning hugepages

Using set_pte_at() does not do the right thing when putting down
HWPOISON swap entries for hugepages on architectures that support
contiguous ptes.

Fix this problem by using set_huge_swap_pte_at() which was introduced to
fix exactly this problem.

Link: http://lkml.kernel.org/r/20170522133604.11392-7-punit.agrawal@arm.com
Signed-off-by: Punit Agrawal <punit.agrawal@arm.com>
Acked-by: Steve Capper <steve.capper@arm.com>
Cc: "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>
Cc: Catalin Marinas <catalin.marinas@arm.com>
Cc: Will Deacon <will.deacon@arm.com>
Cc: Naoya Horiguchi <n-horiguchi@ah.jp.nec.com>
Cc: Mike Kravetz <mike.kravetz@oracle.com>
Cc: Mark Rutland <mark.rutland@arm.com>
Cc: Hillf Danton <hillf.zj@alibaba-inc.com>
Cc: Aneesh Kumar K.V <aneesh.kumar@linux.vnet.ibm.com>
Cc: Michal Hocko <mhocko@suse.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

mm/rmap.c

@@ -1367,15 +1367,18 @@ static bool try_to_unmap_one(struct page *page, struct vm_area_struct *vma,
 		update_hiwater_rss(mm);
 
 		if (PageHWPoison(page) && !(flags & TTU_IGNORE_HWPOISON)) {
+			pteval = swp_entry_to_pte(make_hwpoison_entry(subpage));
 			if (PageHuge(page)) {
 				int nr = 1 << compound_order(page);
 				hugetlb_count_sub(nr, mm);
+				set_huge_swap_pte_at(mm, address,
+						     pvmw.pte, pteval,
+						     vma_mmu_pagesize(vma));
 			} else {
 				dec_mm_counter(mm, mm_counter(page));
+				set_pte_at(mm, address, pvmw.pte, pteval);
 			}
 
-			pteval = swp_entry_to_pte(make_hwpoison_entry(subpage));
-			set_pte_at(mm, address, pvmw.pte, pteval);
 		} else if (pte_unused(pteval)) {
 			/*
 			 * The guest indicated that the page content is of no