[PATCH v1 1/4] mm: move vma_kernel_pagesize() from hugetlb to mm.h

["David Hildenbrand (Arm)" <david@kernel.org>]

In the past, only hugetlb had special "vma_kernel_pagesize()"
requirements, so it provided its own implementation.

In commit 05ea88608d4e ("mm, hugetlbfs: introduce ->pagesize() to
vm_operations_struct") we generalized that approach by providing a
vm_ops->pagesize() callback to be used by device-dax.

Once device-dax started using that callback in commit c1d53b92b95c
("device-dax: implement ->pagesize() for smaps to report MMUPageSize")
it was missed that CONFIG_DEV_DAX does not depend on hugetlb support.

So building a kernel with CONFIG_DEV_DAX but without CONFIG_HUGETLBFS
would not pick up that value.

Fix it by moving vma_kernel_pagesize() to mm.h, providing only a single
implementation. While at it, improve the kerneldoc a bit.

Ideally, we'd move vma_mmu_pagesize() as well to the header. However,
its __weak symbol might be overwritten by a PPC variant in hugetlb code.
So let's leave it in there for now, as it really only matters for some
hugetlb oddities.

This was found by code inspection.

Fixes: c1d53b92b95c ("device-dax: implement ->pagesize() for smaps to report MMUPageSize")
Cc: Dan Williams <dan.j.williams@intel.com>
Signed-off-by: David Hildenbrand (Arm) <david@kernel.org>
---
 include/linux/hugetlb.h |  7 -------
 include/linux/mm.h      | 20 ++++++++++++++++++++
 mm/hugetlb.c            | 17 -----------------
 3 files changed, 20 insertions(+), 24 deletions(-)

diff --git a/include/linux/hugetlb.h b/include/linux/hugetlb.h
index 65910437be1c..44c1848a2c21 100644
--- a/include/linux/hugetlb.h
+++ b/include/linux/hugetlb.h
@@ -777,8 +777,6 @@ static inline unsigned long huge_page_size(const struct hstate *h)
 	return (unsigned long)PAGE_SIZE << h->order;
 }
 
-extern unsigned long vma_kernel_pagesize(struct vm_area_struct *vma);
-
 extern unsigned long vma_mmu_pagesize(struct vm_area_struct *vma);
 
 static inline unsigned long huge_page_mask(struct hstate *h)
@@ -1177,11 +1175,6 @@ static inline unsigned long huge_page_mask(struct hstate *h)
 	return PAGE_MASK;
 }
 
-static inline unsigned long vma_kernel_pagesize(struct vm_area_struct *vma)
-{
-	return PAGE_SIZE;
-}
-
 static inline unsigned long vma_mmu_pagesize(struct vm_area_struct *vma)
 {
 	return PAGE_SIZE;
diff --git a/include/linux/mm.h b/include/linux/mm.h
index 44e04a42fe77..227809790f1a 100644
--- a/include/linux/mm.h
+++ b/include/linux/mm.h
@@ -1307,6 +1307,26 @@ static inline bool vma_is_shared_maywrite(const struct vm_area_struct *vma)
 	return is_shared_maywrite(&vma->flags);
 }
 
+/**
+ * vma_kernel_pagesize - Default page size granularity for this VMA.
+ * @vma: The user mapping.
+ *
+ * The kernel page size specifies in which granularity VMA modifications
+ * can be performed. Folios in this VMA will be aligned to, and at least
+ * the size of the number of bytes returned by this function.
+ *
+ * The default kernel page size is not affected by Transparent Huge Pages
+ * being in effect.
+ *
+ * Return: The default page size granularity for this VMA.
+ */
+static inline unsigned long vma_kernel_pagesize(struct vm_area_struct *vma)
+{
+	if (unlikely(vma->vm_ops && vma->vm_ops->pagesize))
+		return vma->vm_ops->pagesize(vma);
+	return PAGE_SIZE;
+}
+
 static inline
 struct vm_area_struct *vma_find(struct vma_iterator *vmi, unsigned long max)
 {
diff --git a/mm/hugetlb.c b/mm/hugetlb.c
index 1d41fa3dd43e..66eadfa9e958 100644
--- a/mm/hugetlb.c
+++ b/mm/hugetlb.c
@@ -1017,23 +1017,6 @@ static pgoff_t vma_hugecache_offset(struct hstate *h,
 			(vma->vm_pgoff >> huge_page_order(h));
 }
 
-/**
- * vma_kernel_pagesize - Page size granularity for this VMA.
- * @vma: The user mapping.
- *
- * Folios in this VMA will be aligned to, and at least the size of the
- * number of bytes returned by this function.
- *
- * Return: The default size of the folios allocated when backing a VMA.
- */
-unsigned long vma_kernel_pagesize(struct vm_area_struct *vma)
-{
-	if (vma->vm_ops && vma->vm_ops->pagesize)
-		return vma->vm_ops->pagesize(vma);
-	return PAGE_SIZE;
-}
-EXPORT_SYMBOL_GPL(vma_kernel_pagesize);
-
 /*
  * Return the page size being used by the MMU to back a VMA. In the majority
  * of cases, the page size used by the kernel matches the MMU size. On
-- 
2.43.0