[PATCH RFC 2/5] mm: Extend copy_vma()

[Kirill Tkhai <ktkhai@virtuozzo.com>]

This prepares the function to copy a vma between
two processes. Two new arguments are introduced.

Signed-off-by: Kirill Tkhai <ktkhai@virtuozzo.com>
---
 include/linux/mm.h |    4 ++--
 mm/mmap.c          |   33 ++++++++++++++++++++++++---------
 mm/mremap.c        |    4 ++--
 3 files changed, 28 insertions(+), 13 deletions(-)

diff --git a/include/linux/mm.h b/include/linux/mm.h
index 0e8834ac32b7..afe07e4a76f8 100644
--- a/include/linux/mm.h
+++ b/include/linux/mm.h
@@ -2329,8 +2329,8 @@ extern void __vma_link_rb(struct mm_struct *, struct vm_area_struct *,
 	struct rb_node **, struct rb_node *);
 extern void unlink_file_vma(struct vm_area_struct *);
 extern struct vm_area_struct *copy_vma(struct vm_area_struct **,
-	unsigned long addr, unsigned long len, pgoff_t pgoff,
-	bool *need_rmap_locks);
+	struct mm_struct *, unsigned long addr, unsigned long len,
+	pgoff_t pgoff, bool *need_rmap_locks, bool clear_flags_ctx);
 extern void exit_mmap(struct mm_struct *);
 
 static inline int check_data_rlimit(unsigned long rlim,
diff --git a/mm/mmap.c b/mm/mmap.c
index 9cf52bdb22a8..46266f6825ae 100644
--- a/mm/mmap.c
+++ b/mm/mmap.c
@@ -3194,19 +3194,21 @@ int insert_vm_struct(struct mm_struct *mm, struct vm_area_struct *vma)
 }
 
 /*
- * Copy the vma structure to a new location in the same mm,
- * prior to moving page table entries, to effect an mremap move.
+ * Copy the vma structure to new location in the same vma
+ * prior to moving page table entries, to effect an mremap move;
  */
 struct vm_area_struct *copy_vma(struct vm_area_struct **vmap,
-	unsigned long addr, unsigned long len, pgoff_t pgoff,
-	bool *need_rmap_locks)
+				struct mm_struct *mm, unsigned long addr,
+				unsigned long len, pgoff_t pgoff,
+				bool *need_rmap_locks, bool clear_flags_ctx)
 {
 	struct vm_area_struct *vma = *vmap;
 	unsigned long vma_start = vma->vm_start;
-	struct mm_struct *mm = vma->vm_mm;
+	struct vm_userfaultfd_ctx uctx;
 	struct vm_area_struct *new_vma, *prev;
 	struct rb_node **rb_link, *rb_parent;
 	bool faulted_in_anon_vma = true;
+	unsigned long flags;
 
 	/*
 	 * If anonymous vma has not yet been faulted, update new pgoff
@@ -3219,15 +3221,25 @@ struct vm_area_struct *copy_vma(struct vm_area_struct **vmap,
 
 	if (find_vma_links(mm, addr, addr + len, &prev, &rb_link, &rb_parent))
 		return NULL;	/* should never get here */
-	new_vma = vma_merge(mm, prev, addr, addr + len, vma->vm_flags,
-			    vma->anon_vma, vma->vm_file, pgoff, vma_policy(vma),
-			    vma->vm_userfaultfd_ctx);
+
+	uctx = vma->vm_userfaultfd_ctx;
+	flags = vma->vm_flags;
+	if (clear_flags_ctx) {
+		uctx = NULL_VM_UFFD_CTX;
+		flags &= ~(VM_UFFD_MISSING | VM_UFFD_WP | VM_MERGEABLE |
+			   VM_LOCKED | VM_LOCKONFAULT | VM_WIPEONFORK |
+			   VM_DONTCOPY);
+	}
+
+	new_vma = vma_merge(mm, prev, addr, addr + len, flags, vma->anon_vma,
+			    vma->vm_file, pgoff, vma_policy(vma), uctx);
 	if (new_vma) {
 		/*
 		 * Source vma may have been merged into new_vma
 		 */
 		if (unlikely(vma_start >= new_vma->vm_start &&
-			     vma_start < new_vma->vm_end)) {
+			     vma_start < new_vma->vm_end) &&
+			     vma->vm_mm == mm) {
 			/*
 			 * The only way we can get a vma_merge with
 			 * self during an mremap is if the vma hasn't
@@ -3248,6 +3260,9 @@ struct vm_area_struct *copy_vma(struct vm_area_struct **vmap,
 		new_vma = vm_area_dup(vma);
 		if (!new_vma)
 			goto out;
+		new_vma->vm_mm = mm;
+		new_vma->vm_flags = flags;
+		new_vma->vm_userfaultfd_ctx = uctx;
 		new_vma->vm_start = addr;
 		new_vma->vm_end = addr + len;
 		new_vma->vm_pgoff = pgoff;
diff --git a/mm/mremap.c b/mm/mremap.c
index 37b5b2ad91be..9a96cfc28675 100644
--- a/mm/mremap.c
+++ b/mm/mremap.c
@@ -352,8 +352,8 @@ static unsigned long move_vma(struct vm_area_struct *vma,
 		return err;
 
 	new_pgoff = vma->vm_pgoff + ((old_addr - vma->vm_start) >> PAGE_SHIFT);
-	new_vma = copy_vma(&vma, new_addr, new_len, new_pgoff,
-			   &need_rmap_locks);
+	new_vma = copy_vma(&vma, mm, new_addr, new_len, new_pgoff,
+			   &need_rmap_locks, false);
 	if (!new_vma)
 		return -ENOMEM;