[PATCH v7 2/4] userfaultfd: split mwriteprotect_range()

[Muhammad Usama Anjum]

Split mwriteprotect_range() to create a unlocked version. This
will be used in the next patch to write protect a memory area.
Add a helper function, wp_range_async() as well.

Signed-off-by: Muhammad Usama Anjum <usama.anjum@xxxxxxxxxxxxx>
---
 fs/userfaultfd.c              | 11 ++++++++++
 include/linux/userfaultfd_k.h | 10 +++++++++
 mm/userfaultfd.c              | 40 ++++++++++++++++++++++-------------
 3 files changed, 46 insertions(+), 15 deletions(-)

diff --git a/fs/userfaultfd.c b/fs/userfaultfd.c
index be5e10d15058..5ff5ff4314e3 100644
--- a/fs/userfaultfd.c
+++ b/fs/userfaultfd.c
@@ -1967,6 +1967,17 @@ static int userfaultfd_continue(struct userfaultfd_ctx *ctx, unsigned long arg)
 	return ret;
 }
 
+int wp_range_async(struct vm_area_struct *vma, unsigned long start, unsigned long len)
+{
+	struct userfaultfd_ctx *ctx = vma->vm_userfaultfd_ctx.ctx;
+
+	if (!ctx)
+		return -1;
+
+	ctx->async = true;
+	return __mwriteprotect_range(ctx->mm, start, len, true, &ctx->mmap_changing);
+}
+
 static inline unsigned int uffd_ctx_features(__u64 user_features)
 {
 	/*
diff --git a/include/linux/userfaultfd_k.h b/include/linux/userfaultfd_k.h
index 9df0b9a762cc..fba05a32f8e9 100644
--- a/include/linux/userfaultfd_k.h
+++ b/include/linux/userfaultfd_k.h
@@ -73,6 +73,9 @@ extern ssize_t mcopy_continue(struct mm_struct *dst_mm, unsigned long dst_start,
 extern int mwriteprotect_range(struct mm_struct *dst_mm,
 			       unsigned long start, unsigned long len,
 			       bool enable_wp, atomic_t *mmap_changing);
+extern int __mwriteprotect_range(struct mm_struct *dst_mm,
+				 unsigned long start, unsigned long len,
+				 bool enable_wp, atomic_t *mmap_changing);
 extern void uffd_wp_range(struct mm_struct *dst_mm, struct vm_area_struct *vma,
 			  unsigned long start, unsigned long len, bool enable_wp);
 
@@ -179,6 +182,8 @@ extern int userfaultfd_unmap_prep(struct mm_struct *mm, unsigned long start,
 				  unsigned long end, struct list_head *uf);
 extern void userfaultfd_unmap_complete(struct mm_struct *mm,
 				       struct list_head *uf);
+extern int wp_range_async(struct vm_area_struct *vma, unsigned long start,
+			  unsigned long len);
 
 #else /* CONFIG_USERFAULTFD */
 
@@ -274,6 +279,11 @@ static inline bool uffd_disable_fault_around(struct vm_area_struct *vma)
 	return false;
 }
 
+int wp_range_async(struct vm_area_struct *vma, unsigned long start, unsigned long len)
+{
+	return -1;
+}
+
 #endif /* CONFIG_USERFAULTFD */
 
 static inline bool pte_marker_entry_uffd_wp(swp_entry_t entry)
diff --git a/mm/userfaultfd.c b/mm/userfaultfd.c
index 65ad172add27..9d8a43faf764 100644
--- a/mm/userfaultfd.c
+++ b/mm/userfaultfd.c
@@ -734,25 +734,13 @@ void uffd_wp_range(struct mm_struct *dst_mm, struct vm_area_struct *dst_vma,
 	tlb_finish_mmu(&tlb);
 }
 
-int mwriteprotect_range(struct mm_struct *dst_mm, unsigned long start,
-			unsigned long len, bool enable_wp,
-			atomic_t *mmap_changing)
+int __mwriteprotect_range(struct mm_struct *dst_mm, unsigned long start,
+			  unsigned long len, bool enable_wp,
+			  atomic_t *mmap_changing)
 {
 	struct vm_area_struct *dst_vma;
 	unsigned long page_mask;
 	int err;
-
-	/*
-	 * Sanitize the command parameters:
-	 */
-	BUG_ON(start & ~PAGE_MASK);
-	BUG_ON(len & ~PAGE_MASK);
-
-	/* Does the address range wrap, or is the span zero-sized? */
-	BUG_ON(start + len <= start);
-
-	mmap_read_lock(dst_mm);
-
 	/*
 	 * If memory mappings are changing because of non-cooperative
 	 * operation (e.g. mremap) running in parallel, bail out and
@@ -783,6 +771,28 @@ int mwriteprotect_range(struct mm_struct *dst_mm, unsigned long start,
 
 	err = 0;
 out_unlock:
+	return err;
+}
+
+int mwriteprotect_range(struct mm_struct *dst_mm, unsigned long start,
+			unsigned long len, bool enable_wp,
+			atomic_t *mmap_changing)
+{
+	int err;
+
+	/*
+	 * Sanitize the command parameters:
+	 */
+	BUG_ON(start & ~PAGE_MASK);
+	BUG_ON(len & ~PAGE_MASK);
+
+	/* Does the address range wrap, or is the span zero-sized? */
+	BUG_ON(start + len <= start);
+
+	mmap_read_lock(dst_mm);
+
+	err = __mwriteprotect_range(dst_mm, start, len, enable_wp, mmap_changing);
+
 	mmap_read_unlock(dst_mm);
 	return err;
 }
-- 
2.30.2