[PATCH v3] mm/memory-failure: fix infinite UCE for VM_PFNMAP pfn

[Jinjiang Tu <tujinjiang@huawei.com>]

When memory_failure() is called for a already hwpoisoned pfn,
kill_accessing_process() will be called to kill current task. However, if
the vma of the accessing vaddr is VM_PFNMAP, walk_page_range() will skip
the vma in walk_page_test() and return 0.

Before commit aaf99ac2ceb7 ("mm/hwpoison: do not send SIGBUS to processes
with recovered clean pages"), kill_accessing_process() will return EFAULT.
For x86, the current task will be killed in kill_me_maybe().

However, after this commit, kill_accessing_process() simplies return 0,
that means UCE is handled properly, but it doesn't actually. In such case,
the user task will trigger UCE infinitely.

To fix it, add .test_walk callback for hwpoison_walk_ops to scan all vmas.

Fixes: aaf99ac2ceb7 ("mm/hwpoison: do not send SIGBUS to processes with recovered clean pages")
Acked-by: David Hildenbrand <david@redhat.com>
Acked-by: Miaohe Lin <linmiaohe@huawei.com>
Reviewed-by: Jane Chu <jane.chu@oracle.com>
Cc: <stable@vger.kernel.org>
Signed-off-by: Jinjiang Tu <tujinjiang@huawei.com>
---

Changelog since v2:
 * add a comment and cc stable

Changelog since v1:
 * update patch description, suggested by David Hildenbrand 

 mm/memory-failure.c | 8 ++++++++
 1 file changed, 8 insertions(+)

diff --git a/mm/memory-failure.c b/mm/memory-failure.c
index e2e685b971bb..fc30ca4804bf 100644
--- a/mm/memory-failure.c
+++ b/mm/memory-failure.c
@@ -853,9 +853,17 @@ static int hwpoison_hugetlb_range(pte_t *ptep, unsigned long hmask,
 #define hwpoison_hugetlb_range	NULL
 #endif
 
+static int hwpoison_test_walk(unsigned long start, unsigned long end,
+			     struct mm_walk *walk)
+{
+	/* We also want to consider pages mapped into VM_PFNMAP. */
+	return 0;
+}
+
 static const struct mm_walk_ops hwpoison_walk_ops = {
 	.pmd_entry = hwpoison_pte_range,
 	.hugetlb_entry = hwpoison_hugetlb_range,
+	.test_walk = hwpoison_test_walk,
 	.walk_lock = PGWALK_RDLOCK,
 };
 
-- 
2.43.0