From d13ba37a34cf71d69858586382a7034ec2519751 Mon Sep 17 00:00:00 2001
From: "Liam R. Howlett" <Liam.Howlett@oracle.com>
Date: Thu, 5 May 2022 13:51:19 -0700
Subject: [PATCH] mm/mmap: Introduce sub_vma() and use it in __split_vma()

sub_vma() creates a vma that covers a subset of the addresses covered by
the larger vma.  Use this new function in __split_vma() and in later
commits of the series.

Signed-off-by: Liam R. Howlett <Liam.Howlett@oracle.com>
---
 mm/mmap.c | 118 ++++++++++++++++++++++++++++++++----------------------
 1 file changed, 70 insertions(+), 48 deletions(-)

diff --git a/mm/mmap.c b/mm/mmap.c
index 2dc1de1cbd99..443c0a06656d 100644
--- a/mm/mmap.c
+++ b/mm/mmap.c
@@ -2273,6 +2273,63 @@ static inline int vma_replace(struct vm_area_struct *vma,
 	return 0;
 }
 
+/**
+ * sub_vma() - Create a vma that covers a part of another vma
+ * @mm: The mm_struct
+ * @vma: The large vma
+ * @new_vma: Pointer for the new vma
+ * @start: The start address
+ * @end: The end address
+ *
+ * Will clone the anon vma, take a ref to a file, call vm_ops open if needed.
+ * Returns: 0 on success
+ */
+int sub_vma(struct mm_struct *mm, struct vm_area_struct *vma,
+	struct vm_area_struct **new_vma, unsigned long start, unsigned long end)
+{
+	int err = -ENOMEM;
+
+	BUG_ON(vma->vm_start > end);
+	BUG_ON(vma->vm_end < start);
+	BUG_ON(start > end);
+
+	(*new_vma) = vm_area_dup(vma);
+	if (!(*new_vma))
+		return err;
+
+	if (start == vma->vm_start) {
+		(*new_vma)->vm_end = end;
+		(*new_vma)->vm_pgoff = vma->vm_pgoff;
+	} else {
+		(*new_vma)->vm_start = start;
+		(*new_vma)->vm_pgoff += ((start - vma->vm_start) >> PAGE_SHIFT);
+	}
+
+	err = vma_dup_policy(vma, *new_vma);
+	if (err)
+		goto no_new_vma_policy;
+
+	err = anon_vma_clone(*new_vma, vma);
+	if (err)
+		goto no_new_vma_anon;
+
+	if ((*new_vma)->vm_file) {
+		get_file((*new_vma)->vm_file);
+	}
+
+	if ((*new_vma)->vm_ops && (*new_vma)->vm_ops->open) {
+		(*new_vma)->vm_ops->open(*new_vma);
+	}
+
+	return 0;
+
+no_new_vma_anon:
+	mpol_put(vma_policy(*new_vma));
+no_new_vma_policy:
+	vm_area_free(*new_vma);
+	*new_vma = NULL;
+	return err;
+}
 /*
  * __split_vma() - Split one VMA into two new VMAs.
  * @mm: The mm_struct
@@ -2290,51 +2347,19 @@ int __split_vma(struct mm_struct *mm, struct vm_area_struct **vma,
 	struct vm_area_struct *start, *end;
 	int err;
 	validate_mm_mt(mm);
-
 	if ((*vma)->vm_ops && (*vma)->vm_ops->may_split) {
 		err = (*vma)->vm_ops->may_split(*vma, addr);
 		if (err)
 			return err;
 	}
 
-	err = -ENOMEM;
-	start = vm_area_dup(*vma);
-	if (!start)
-		goto no_start;
-
-	end = vm_area_dup(*vma);
-	if (!end)
-		goto no_end;
-
-	start->vm_end = addr;
-	end->vm_start = addr;
-	end->vm_pgoff += ((addr - start->vm_start) >> PAGE_SHIFT);
-
-	err = vma_dup_policy(*vma, start);
+	err = sub_vma(mm, *vma, &start, (*vma)->vm_start, addr);
 	if (err)
-		goto no_start_policy;
-
-	err = vma_dup_policy(*vma, end);
-	if (err)
-		goto no_end_policy;
-
-	err = anon_vma_clone(start, *vma);
-	if (err)
-		goto no_start_anon;
+		goto no_start;
 
-	err = anon_vma_clone(end, *vma);
+	err = sub_vma(mm, *vma, &end, addr, (*vma)->vm_end);
 	if (err)
-		goto no_end_anon;
-
-	if (start->vm_file) {
-		get_file(start->vm_file);
-		get_file(end->vm_file);
-	}
-
-	if (start->vm_ops && start->vm_ops->open) {
-		start->vm_ops->open(start);
-		end->vm_ops->open(end);
-	}
+		goto no_end;
 
 
 	if (vma_replace(*vma, start, end))
@@ -2348,24 +2373,21 @@ int __split_vma(struct mm_struct *mm, struct vm_area_struct **vma,
 
 no_replace:
 	/* Clean everything up if vma_replace failed. */
-	if (start->vm_ops && start->vm_ops->close) {
-		start->vm_ops->close(start);
+	if (end->vm_ops && end->vm_ops->close)
 		end->vm_ops->close(end);
-	}
-	if (start->vm_file) {
-		fput(start->vm_file);
+	if (end->vm_file)
 		fput(end->vm_file);
-	}
 	unlink_anon_vmas(end);
-no_end_anon:
-	unlink_anon_vmas(start);
-no_start_anon:
 	mpol_put(vma_policy(end));
-no_end_policy:
-	mpol_put(vma_policy(start));
-no_start_policy:
 	vm_area_free(end);
+
 no_end:
+	if (start->vm_ops && start->vm_ops->close)
+		start->vm_ops->close(start);
+	if (start->vm_file)
+		fput(start->vm_file);
+	unlink_anon_vmas(start);
+	mpol_put(vma_policy(start));
 	vm_area_free(start);
 no_start:
 	validate_mm_mt(mm);
-- 
2.50.1