[PATCH] arm64: hugetlb: Fix huge_pte_offset to return poisoned pmd

[Punit Agrawal]

When memory failure is enabled, a poisoned hugepage PMD is marked as a
swap entry. As pmd_present() only checks for VALID and PROT_NONE
bits (turned off for swap entries), it causues huge_pte_offset() to
return NULL for poisoned PMDs.

This behaviour of huge_pte_offset() leads to the error such as below
when munmap is called on poisoned hugepages.

[  344.165544] mm/pgtable-generic.c:33: bad pmd 000000083af00074.

Fix huge_pte_offset() to return the poisoned PMD which is then
appropriately handled by the generic layer code.

Signed-off-by: Punit Agrawal <punit.agrawal@xxxxxxx>
Cc: Catalin Marinas <catalin.marinas@xxxxxxx>
Cc: Steve Capper <steve.capper@xxxxxxx>
---
 arch/arm64/mm/hugetlbpage.c | 11 ++++++++++-
 1 file changed, 10 insertions(+), 1 deletion(-)

diff --git a/arch/arm64/mm/hugetlbpage.c b/arch/arm64/mm/hugetlbpage.c
index e25584d72396..9263f206353c 100644
--- a/arch/arm64/mm/hugetlbpage.c
+++ b/arch/arm64/mm/hugetlbpage.c
@@ -150,8 +150,17 @@ pte_t *huge_pte_offset(struct mm_struct *mm, unsigned long addr)
        if (pud_huge(*pud))
                return (pte_t *)pud;
        pmd = pmd_offset(pud, addr);
+
+       /*
+        * In case of HW Poisoning, a hugepage pmd can contain
+        * poisoned entries. Poisoned entries are marked as swap
+        * entries.
+        *
+        * For pmds that are not present, check to see if it could be
+        * a swap entry (!present and !none) before giving up.
+        */
        if (!pmd_present(*pmd))
-               return NULL;
+               return !pmd_none(*pmd) ? (pte_t *)pmd : NULL;

        if (pte_cont(pmd_pte(*pmd))) {
                pmd = pmd_offset(
--
2.11.0