mm/gup: Expose mm_populate_vma() for use when the vma is known

When a vma is known, avoid calling mm_populate to search for the vma to
populate.

Signed-off-by: Liam R. Howlett <Liam.Howlett@Oracle.com>

include/linux/mm.h

@@ -2587,8 +2587,12 @@ static inline void mm_populate(unsigned long addr, unsigned long len)
 	/* Ignore errors */
 	(void) __mm_populate(addr, len, 1);
 }
+extern void mm_populate_vma(struct vm_area_struct *vma, unsigned long start,
+			    unsigned long end);
 #else
 static inline void mm_populate(unsigned long addr, unsigned long len) {}
+void mm_populate_vma(struct vm_area_struct *vma, unsigned long start,
+		     unsigned long end) {}
 #endif
 
 /* These take the mm semaphore themselves */

mm/gup.c

@@ -1431,6 +1431,26 @@ long populate_vma_page_range(struct vm_area_struct *vma,
 				NULL, NULL, locked);
 }
 
+/*
+ * mm_populate_vma() - Populate a single range in a single vma.
+ * @vma: The vma to populate.
+ * @start: The start address to populate
+ * @end: The end address to stop populating
+ *
+ * Note: Ignores errors.
+ */
+void mm_populate_vma(struct vm_area_struct *vma, unsigned long start,
+		unsigned long end)
+{
+	struct mm_struct *mm = current->mm;
+	int locked = 1;
+
+	mmap_read_lock(mm);
+	populate_vma_page_range(vma, start, end, &locked);
+	if (locked)
+		mmap_read_unlock(mm);
+}
+
 /*
  * __mm_populate - populate and/or mlock pages within a range of address space.
  *