[PATCH v2 1/4] mm/swapfile: fix wrong swap entry type for hwpoisoned swapcache page

[Miaohe Lin]

Hwpoisoned dirty swap cache page is kept in the swap cache and there's
simple interception code in do_swap_page() to catch it. But when trying
to swapoff, unuse_pte() will wrongly install a general sense of "future
accesses are invalid" swap entry for hwpoisoned swap cache page due to
unaware of such type of page. The user will receive SIGBUS signal without
expected BUS_MCEERR_AR payload. BTW, typo 'hwposioned' is fixed.

Fixes: 6b970599e807 ("mm: hwpoison: support recovery from ksm_might_need_to_copy()")
Signed-off-by: Miaohe Lin <linmiaohe@xxxxxxxxxx>
---
 mm/ksm.c      | 2 ++
 mm/swapfile.c | 8 ++++----
 2 files changed, 6 insertions(+), 4 deletions(-)

diff --git a/mm/ksm.c b/mm/ksm.c
index 97a9627116fa..74804158ee02 100644
--- a/mm/ksm.c
+++ b/mm/ksm.c
@@ -2794,6 +2794,8 @@ struct page *ksm_might_need_to_copy(struct page *page,
 			anon_vma->root == vma->anon_vma->root) {
 		return page;		/* still no need to copy it */
 	}
+	if (PageHWPoison(page))
+		return ERR_PTR(-EHWPOISON);
 	if (!PageUptodate(page))
 		return page;		/* let do_swap_page report the error */
 
diff --git a/mm/swapfile.c b/mm/swapfile.c
index e04eb9c0482d..0df94c4000ea 100644
--- a/mm/swapfile.c
+++ b/mm/swapfile.c
@@ -1744,7 +1744,7 @@ static int unuse_pte(struct vm_area_struct *vma, pmd_t *pmd,
 	struct page *swapcache;
 	spinlock_t *ptl;
 	pte_t *pte, new_pte, old_pte;
-	bool hwposioned = false;
+	bool hwpoisoned = PageHWPoison(page);
 	int ret = 1;
 
 	swapcache = page;
@@ -1752,7 +1752,7 @@ static int unuse_pte(struct vm_area_struct *vma, pmd_t *pmd,
 	if (unlikely(!page))
 		return -ENOMEM;
 	else if (unlikely(PTR_ERR(page) == -EHWPOISON))
-		hwposioned = true;
+		hwpoisoned = true;
 
 	pte = pte_offset_map_lock(vma->vm_mm, pmd, addr, &ptl);
 	if (unlikely(!pte || !pte_same_as_swp(ptep_get(pte),
@@ -1763,11 +1763,11 @@ static int unuse_pte(struct vm_area_struct *vma, pmd_t *pmd,
 
 	old_pte = ptep_get(pte);
 
-	if (unlikely(hwposioned || !PageUptodate(page))) {
+	if (unlikely(hwpoisoned || !PageUptodate(page))) {
 		swp_entry_t swp_entry;
 
 		dec_mm_counter(vma->vm_mm, MM_SWAPENTS);
-		if (hwposioned) {
+		if (hwpoisoned) {
 			swp_entry = make_hwpoison_entry(swapcache);
 			page = swapcache;
 		} else {
-- 
2.33.0