[PATCH v4 10/14] mm/userfaultfd: Support COW PTE

[Chih-En Lin <shiyn.lin@gmail.com>]

If uffd fills the zeropage or installs to COW-ed PTE, break it first.

Signed-off-by: Chih-En Lin <shiyn.lin@gmail.com>
---
 mm/userfaultfd.c | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/mm/userfaultfd.c b/mm/userfaultfd.c
index 0499907b6f1a..3f66aa3eb54f 100644
--- a/mm/userfaultfd.c
+++ b/mm/userfaultfd.c
@@ -70,6 +70,9 @@ int mfill_atomic_install_pte(struct mm_struct *dst_mm, pmd_t *dst_pmd,
 	struct inode *inode;
 	pgoff_t offset, max_off;
 
+	if (break_cow_pte(dst_vma, dst_pmd, dst_addr))
+		return -ENOMEM;
+
 	_dst_pte = mk_pte(page, dst_vma->vm_page_prot);
 	_dst_pte = pte_mkdirty(_dst_pte);
 	if (page_in_cache && !vm_shared)
@@ -229,6 +232,9 @@ static int mfill_zeropage_pte(struct mm_struct *dst_mm,
 	pgoff_t offset, max_off;
 	struct inode *inode;
 
+	if (break_cow_pte(dst_vma, dst_pmd, dst_addr))
+		return -ENOMEM;
+
 	_dst_pte = pte_mkspecial(pfn_pte(my_zero_pfn(dst_addr),
 					 dst_vma->vm_page_prot));
 	dst_pte = pte_offset_map_lock(dst_mm, dst_pmd, dst_addr, &ptl);
-- 
2.34.1