[PATCH v2 14/24] shmem/userfaultfd: Pass over uffd-wp special swap pte when fork()

Peter Xu
2021-04-27T16:24:02Z

It should be handled similarly like other uffd-wp wr-protected ptes: we should
pass it over when the dst_vma has VM_UFFD_WP armed, otherwise drop it.

Signed-off-by: Peter Xu <peterx@redhat.com>
---
mm/memory.c | 15 ++++++++++++++-
1 file changed, 14 insertions(+), 1 deletion(-)

diff --git a/mm/memory.c b/mm/memory.c
index 872fb59192277..f1cdc613b5887 100644
--- a/mm/memory.c
+++ b/mm/memory.c
@@ -715,8 +715,21 @@ copy_nonpresent_pte(struct mm_struct *dst_mm, struct mm_struct *src_mm,
unsigned long vm_flags = dst_vma->vm_flags;
pte_t pte = *src_pte;
struct page *page;
- swp_entry_t entry = pte_to_swp_entry(pte);
+ swp_entry_t entry;
+
+ if (unlikely(is_swap_special_pte(pte))) {
+ /*
+ * uffd-wp special swap pte is the only possibility for now.
+ * If dst vma is registered with uffd-wp, copy it over.
+ * Otherwise, ignore this pte as if it's a none pte would work.
+ */
+ WARN_ON_ONCE(!pte_swp_uffd_wp_special(pte));
+ if (userfaultfd_wp(dst_vma))
+ set_pte_at(dst_mm, addr, dst_pte, pte);
+ return 0;
+ }

+ entry = pte_to_swp_entry(pte);
if (likely(!non_swap_entry(entry))) {
if (swap_duplicate(entry) < 0)
return entry.val;
--
2.26.2