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From:   Liam Howlett <liam.howlett@oracle.com>
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        Liam Howlett <liam.howlett@oracle.com>
Subject: [PATCH 01/22] mm: Add vma_lookup()
Thread-Topic: [PATCH 01/22] mm: Add vma_lookup()
Thread-Index: AQHXRb2/5QqU4ByieE67cOKQO9MokQ==
Date:   Mon, 10 May 2021 16:58:49 +0000
Message-ID: <20210510165839.2692974-2-Liam.Howlett@Oracle.com>
References: <20210510165839.2692974-1-Liam.Howlett@Oracle.com>
In-Reply-To: <20210510165839.2692974-1-Liam.Howlett@Oracle.com>
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Many places in the kernel use find_vma() to get a vma and then check the
start address of the vma to ensure the next vma was not returned.

Other places use the find_vma_intersection() call with add, addr + 1 as
the range; looking for just the vma at a specific address.

The third use of find_vma() is by developers who do not know that the
function starts searching at the provided address upwards for the next
vma.  This results in a bug that is often overlooked for a long time.

Adding the new vma_lookup() function will allow for cleaner code by
removing the find_vma() calls which check limits, making
find_vma_intersection() calls of a single address to be shorter, and
potentially reduce the incorrect uses of find_vma().

Signed-off-by: Liam R. Howlett <Liam.Howlett@Oracle.com>
---
 include/linux/mm.h | 18 ++++++++++++++++++
 1 file changed, 18 insertions(+)

diff --git a/include/linux/mm.h b/include/linux/mm.h
index 25b9041f9925..5f2a15e702ff 100644
--- a/include/linux/mm.h
+++ b/include/linux/mm.h
@@ -2689,6 +2689,24 @@ static inline struct vm_area_struct * find_vma_inter=
section(struct mm_struct * m
 	return vma;
 }
=20
+/**
+ * vma_lookup() - Find a VMA at a specific address
+ * @mm: The process address space.
+ * @addr: The user address.
+ *
+ * Return: The vm_area_struct at the given address, %NULL otherwise.
+ */
+static inline
+struct vm_area_struct *vma_lookup(struct mm_struct *mm, unsigned long addr=
)
+{
+	struct vm_area_struct * vma =3D find_vma(mm, addr);
+
+	if (vma && addr < vma->vm_start)
+		vma =3D NULL;
+
+	return vma;
+}
+
 static inline unsigned long vm_start_gap(struct vm_area_struct *vma)
 {
 	unsigned long vm_start =3D vma->vm_start;
--=20
2.30.2