[PATCH 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.

Fixes: 6b970599e807 ("mm: hwpoison: support recovery from ksm_might_need_to_copy()")
Signed-off-by: Miaohe Lin <linmiaohe@xxxxxxxxxx>
---
 mm/swapfile.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/mm/swapfile.c b/mm/swapfile.c
index 346e22b8ae97..02f6808e65bf 100644
--- a/mm/swapfile.c
+++ b/mm/swapfile.c
@@ -1767,7 +1767,8 @@ static int unuse_pte(struct vm_area_struct *vma, pmd_t *pmd,
 		swp_entry_t swp_entry;
 
 		dec_mm_counter(vma->vm_mm, MM_SWAPENTS);
-		if (hwposioned) {
+		/* Hwpoisoned swapcache page is also !PageUptodate. */
+		if (hwposioned || PageHWPoison(page)) {
 			swp_entry = make_hwpoison_entry(swapcache);
 			page = swapcache;
 		} else {
-- 
2.33.0