linux-kernel - [PATCH v2 1/2] mm/mremap: Clean up vma_to

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Message-ID: <20241018174114.2871880-2-Liam.Howlett@oracle.com>
Date: Fri, 18 Oct 2024 13:41:13 -0400
From: "Liam R. Howlett" <Liam.Howlett@...cle.com>
To: Andrew Morton <akpm@...ux-foundation.org>
Cc: linux-mm@...ck.org, linux-kernel@...r.kernel.org,
        Lorenzo Stoakes <lorenzo.stoakes@...cle.com>,
        Jann Horn <jannh@...gle.com>, David Hildenbrand <david@...hat.com>,
        Qi Zheng <zhengqi.arch@...edance.com>,
        Kefeng Wang <wangkefeng.wang@...wei.com>,
        Jeff Xu <jeffxu@...omium.org>, Pedro Falcato <pedro.falcato@...il.com>,
        "Liam R. Howlett" <Liam.Howlett@...cle.com>
Subject: [PATCH v2 1/2] mm/mremap: Clean up vma_to_resize()

From: "Liam R. Howlett" <Liam.Howlett@...cle.com>

vma_to_resize() is used in two locations to find and validate the vma
for the mremap location.  One of the two locations already has the vma,
which is then re-found to validate the same vma.

This code can be simplified by moving the vma_lookup() from
vma_to_resize() to mremap_to() and changing the return type to an int
error.

Since the function now just validates the vma, the function is renamed
to resize_is_valid() to better reflect what it is doing.

This commit also adds documentation about the function.

Signed-off-by: Liam R. Howlett <Liam.Howlett@...cle.com>
---
 mm/mremap.c | 53 +++++++++++++++++++++++++++++++----------------------
 1 file changed, 31 insertions(+), 22 deletions(-)

diff --git a/mm/mremap.c b/mm/mremap.c
index 5917feafe8cc..e781ec4573ca 100644
--- a/mm/mremap.c
+++ b/mm/mremap.c
@@ -826,17 +826,24 @@ static unsigned long move_vma(struct vm_area_struct *vma,
 	return new_addr;
 }
 
-static struct vm_area_struct *vma_to_resize(unsigned long addr,
+/*
+ * resize_is_valid() - Ensure the vma can be resized to the new length at the give
+ * address.
+ *
+ * @vma: The vma to resize
+ * @addr: The old address
+ * @old_len: The current size
+ * @new_len: The desired size
+ * @flags: The vma flags
+ *
+ * Return 0 on success, error otherwise.
+ */
+static int resize_is_valid(struct vm_area_struct *vma, unsigned long addr,
 	unsigned long old_len, unsigned long new_len, unsigned long flags)
 {
 	struct mm_struct *mm = current->mm;
-	struct vm_area_struct *vma;
 	unsigned long pgoff;
 
-	vma = vma_lookup(mm, addr);
-	if (!vma)
-		return ERR_PTR(-EFAULT);
-
 	/*
 	 * !old_len is a special case where an attempt is made to 'duplicate'
 	 * a mapping.  This makes no sense for private mappings as it will
@@ -847,37 +854,37 @@ static struct vm_area_struct *vma_to_resize(unsigned long addr,
 	 */
 	if (!old_len && !(vma->vm_flags & (VM_SHARED | VM_MAYSHARE))) {
 		pr_warn_once("%s (%d): attempted to duplicate a private mapping with mremap.  This is not supported.\n", current->comm, current->pid);
-		return ERR_PTR(-EINVAL);
+		return -EINVAL;
 	}
 
 	if ((flags & MREMAP_DONTUNMAP) &&
 			(vma->vm_flags & (VM_DONTEXPAND | VM_PFNMAP)))
-		return ERR_PTR(-EINVAL);
+		return -EINVAL;
 
 	/* We can't remap across vm area boundaries */
 	if (old_len > vma->vm_end - addr)
-		return ERR_PTR(-EFAULT);
+		return -EFAULT;
 
 	if (new_len == old_len)
-		return vma;
+		return 0;
 
 	/* Need to be careful about a growing mapping */
 	pgoff = (addr - vma->vm_start) >> PAGE_SHIFT;
 	pgoff += vma->vm_pgoff;
 	if (pgoff + (new_len >> PAGE_SHIFT) < pgoff)
-		return ERR_PTR(-EINVAL);
+		return -EINVAL;
 
 	if (vma->vm_flags & (VM_DONTEXPAND | VM_PFNMAP))
-		return ERR_PTR(-EFAULT);
+		return -EFAULT;
 
 	if (!mlock_future_ok(mm, vma->vm_flags, new_len - old_len))
-		return ERR_PTR(-EAGAIN);
+		return -EAGAIN;
 
 	if (!may_expand_vm(mm, vma->vm_flags,
 				(new_len - old_len) >> PAGE_SHIFT))
-		return ERR_PTR(-ENOMEM);
+		return -ENOMEM;
 
-	return vma;
+	return 0;
 }
 
 static unsigned long mremap_to(unsigned long addr, unsigned long old_len,
@@ -936,12 +943,16 @@ static unsigned long mremap_to(unsigned long addr, unsigned long old_len,
 		old_len = new_len;
 	}
 
-	vma = vma_to_resize(addr, old_len, new_len, flags);
-	if (IS_ERR(vma)) {
-		ret = PTR_ERR(vma);
+	vma = vma_lookup(mm, addr);
+	if (!vma) {
+		ret = -EFAULT;
 		goto out;
 	}
 
+	ret = resize_is_valid(vma, addr, old_len, new_len, flags);
+	if (ret)
+		goto out;
+
 	/* MREMAP_DONTUNMAP expands by old_len since old_len == new_len */
 	if (flags & MREMAP_DONTUNMAP &&
 		!may_expand_vm(mm, vma->vm_flags, old_len >> PAGE_SHIFT)) {
@@ -1114,11 +1125,9 @@ SYSCALL_DEFINE5(mremap, unsigned long, addr, unsigned long, old_len,
 	/*
 	 * Ok, we need to grow..
 	 */
-	vma = vma_to_resize(addr, old_len, new_len, flags);
-	if (IS_ERR(vma)) {
-		ret = PTR_ERR(vma);
+	ret = resize_is_valid(vma, addr, old_len, new_len, flags);
+	if (ret)
 		goto out;
-	}
 
 	/* old_len exactly to the end of the area..
 	 */
-- 
2.43.0