I found it by pure code review, that pte_same_as_swp() of unuse_vma() didn't
take uffd-wp bit into account when comparing ptes. pte_same_as_swp() returning
false negative could cause failure to swapoff swap ptes that was wr-protected
by userfaultfd.
Cc: Hugh Dickins <hughd@xxxxxxxxxx>
Cc: Andrea Arcangeli <aarcange@xxxxxxxxxx>
Cc: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
Signed-off-by: Peter Xu <peterx@xxxxxxxxxx>
---
include/linux/swapops.h | 15 +++++++++++----
mm/swapfile.c | 2 +-
2 files changed, 12 insertions(+), 5 deletions(-)
diff --git a/include/linux/swapops.h b/include/linux/swapops.h
index af3d2661e41e..d356ab4047f7 100644
--- a/include/linux/swapops.h
+++ b/include/linux/swapops.h
@@ -23,6 +23,16 @@
#define SWP_TYPE_SHIFT (BITS_PER_XA_VALUE - MAX_SWAPFILES_SHIFT)
#define SWP_OFFSET_MASK ((1UL << SWP_TYPE_SHIFT) - 1)
+/* Clear all flags but only keep swp_entry_t related information */
+static inline pte_t pte_swp_clear_flags(pte_t pte)
+{
+ if (pte_swp_soft_dirty(pte))
+ pte = pte_swp_clear_soft_dirty(pte);
+ if (pte_swp_uffd_wp(pte))
+ pte = pte_swp_clear_uffd_wp(pte);
+ return pte;
+}
+
/*
* Store a type+offset into a swp_entry_t in an arch-independent format
*/
@@ -66,10 +76,7 @@ static inline swp_entry_t pte_to_swp_entry(pte_t pte)
{
swp_entry_t arch_entry;
- if (pte_swp_soft_dirty(pte))
- pte = pte_swp_clear_soft_dirty(pte);
- if (pte_swp_uffd_wp(pte))
- pte = pte_swp_clear_uffd_wp(pte);
+ pte = pte_swp_clear_flags(pte);
arch_entry = __pte_to_swp_entry(pte);
return swp_entry(__swp_type(arch_entry), __swp_offset(arch_entry));
}
diff --git a/mm/swapfile.c b/mm/swapfile.c
index 6212bc033602..1e07d1c776f2 100644
--- a/mm/swapfile.c
+++ b/mm/swapfile.c
@@ -1887,7 +1887,7 @@ unsigned int count_swap_pages(int type, int free)
static inline int pte_same_as_swp(pte_t pte, pte_t swp_pte)
{
- return pte_same(pte_swp_clear_soft_dirty(pte), swp_pte);
+ return pte_same(pte_swp_clear_flags(pte), swp_pte);
}
/*
--
2.31.1
