[RFC,17/30] shmem/userfaultfd: Pass over uffd-wp special swap pte when fork()
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Message ID 20210115170907.24498-18-peterx@redhat.com
State New, archived
Headers show
Series
  • userfaultfd-wp: Support shmem and hugetlbfs
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Commit Message

Peter Xu Jan. 15, 2021, 5:08 p.m. UTC
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(-)

Patch
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diff --git a/mm/memory.c b/mm/memory.c
index f87b5a8a098e..59d56f57ba2c 100644
--- a/mm/memory.c
+++ b/mm/memory.c
@@ -703,8 +703,21 @@  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;