mm: introduce and use vma_end_pgoff()

We already have vma_last_pgoff() which retrieves the last page offset
within a VMA.

However, code often wishes to span a page offset range, which requires the
exclusive end of this range.

So provide this in vma_end_pgoff() and update vma_last_pgoff() to use this
function.

Also update the VMA userland tests to reflect the change.

No functional change intended.

Link: https://lore.kernel.org/20260710-b4-pre-scalable-cow-v2-4-2a5aa403d977@kernel.org
Signed-off-by: Lorenzo Stoakes <ljs@kernel.org>
Reviewed-by: Gregory Price <gourry@gourry.net>
Reviewed-by: Pedro Falcato <pfalcato@suse.de>
Reviewed-by: Vlastimil Babka (SUSE) <vbabka@kernel.org>
Reviewed-by: Zi Yan <ziy@nvidia.com>
Cc: Ackerley Tng <ackerleytng@google.com>
Cc: David Hildenbrand (Arm) <david@kernel.org>
Cc: Kai Huang <kai.huang@intel.com>
Cc: Marek Szyprowski <m.szyprowski@samsung.com>
Cc: SJ Park <sj@kernel.org>
Cc: Thomas Zimmermann <tzimmermann@suse.de>
Cc: Liam R. Howlett (Oracle) <liam@infradead.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

include/linux/mm.h

@@ -4335,6 +4335,23 @@ static inline pgoff_t vma_start_pgoff(const struct vm_area_struct *vma)
 	return vma->vm_pgoff;
 }
 
+/**
+ * vma_end_pgoff() - Get the page offset of the exclusive end of @vma
+ * @vma: The VMA whose end page offset is required.
+ *
+ * This returns the exclusive end page offset of @vma, which is useful for
+ * expressing page offset ranges.
+ *
+ * See the description of vma_start_pgoff() for a description of VMA page
+ * offsets.
+ *
+ * Returns: The exclusive end page offset of @vma.
+ */
+static inline pgoff_t vma_end_pgoff(const struct vm_area_struct *vma)
+{
+	return vma_start_pgoff(vma) + vma_pages(vma);
+}
+
 /**
  * vma_last_pgoff() - Get the page offset of the last page in @vma
  * @vma: The VMA whose last page offset is required.
@@ -4348,7 +4365,7 @@ static inline pgoff_t vma_start_pgoff(const struct vm_area_struct *vma)
  */
 static inline pgoff_t vma_last_pgoff(const struct vm_area_struct *vma)
 {
-	return vma_start_pgoff(vma) + vma_pages(vma) - 1;
+	return vma_end_pgoff(vma) - 1;
 }
 
 static inline unsigned long vma_desc_size(const struct vm_area_desc *desc)

tools/testing/vma/include/dup.h

@@ -1306,6 +1306,11 @@ static inline pgoff_t vma_start_pgoff(const struct vm_area_struct *vma)
 	return vma->vm_pgoff;
 }
 
+static inline pgoff_t vma_end_pgoff(const struct vm_area_struct *vma)
+{
+	return vma_start_pgoff(vma) + vma_pages(vma);
+}
+
 static inline int vfs_mmap_prepare(struct file *file, struct vm_area_desc *desc)
 {
 	return file->f_op->mmap_prepare(desc);