mm: move vma_mmu_pagesize() from hugetlb to vma.c

vma_mmu_pagesize() is also queried on non-hugetlb VMAs and does not really
belong into hugetlb.c.

PPC64 provides a custom overwrite with CONFIG_HUGETLB_PAGE, see
arch/powerpc/mm/book3s64/slice.c, so we cannot easily make this a static
inline function.

So let's move it to vma.c and add some proper kerneldoc.

To make vma tests happy, add a simple vma_kernel_pagesize() stub in
tools/testing/vma/include/custom.h.

Link: https://lkml.kernel.org/r/20260309151901.123947-3-david@kernel.org
Signed-off-by: David Hildenbrand (Arm) <david@kernel.org>
Reviewed-by: Lorenzo Stoakes (Oracle) <ljs@kernel.org>
Acked-by: Mike Rapoport (Microsoft) <rppt@kernel.org>
Cc: "Christophe Leroy (CS GROUP)" <chleroy@kernel.org>
Cc: Dan Williams <dan.j.williams@intel.com>
Cc: Jann Horn <jannh@google.com>
Cc: Liam Howlett <liam.howlett@oracle.com>
Cc: Madhavan Srinivasan <maddy@linux.ibm.com>
Cc: Michael Ellerman <mpe@ellerman.id.au>
Cc: Michal Hocko <mhocko@suse.com>
Cc: Muchun Song <muchun.song@linux.dev>
Cc: Nicholas Piggin <npiggin@gmail.com>
Cc: Oscar Salvador <osalvador@suse.de>
Cc: Paolo Bonzini <pbonzini@redhat.com>
Cc: Pedro Falcato <pfalcato@suse.de>
Cc: Suren Baghdasaryan <surenb@google.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

2 files changed, 21 insertions, 11 deletions

diff --git a/mm/hugetlb.c b/mm/hugetlb.c
index 66761ae5ce71..a786034ac95c 100644
--- a/mm/hugetlb.c
+++ b/mm/hugetlb.c
@@ -1018,17 +1018,6 @@ static pgoff_t vma_hugecache_offset(struct hstate *h,
 }
 
 /*
- * 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
- * architectures where it differs, an architecture-specific 'strong'
- * version of this symbol is required.
- */
-__weak unsigned long vma_mmu_pagesize(struct vm_area_struct *vma)
-{
-	return vma_kernel_pagesize(vma);
-}
-
-/*
  * Flags for MAP_PRIVATE reservations.  These are stored in the bottom
  * bits of the reservation map pointer, which are always clear due to
  * alignment.
diff --git a/mm/vma.c b/mm/vma.c
index be64f781a3aa..e95fd5a5fe5c 100644
--- a/mm/vma.c
+++ b/mm/vma.c
@@ -3300,3 +3300,24 @@ int insert_vm_struct(struct mm_struct *mm, struct vm_area_struct *vma)
 
 	return 0;
 }
+
+/**
+ * vma_mmu_pagesize - Default MMU page size granularity for this VMA.
+ * @vma: The user mapping.
+ *
+ * In the common case, the default page size used by the MMU matches the
+ * default page size used by the kernel (see vma_kernel_pagesize()). On
+ * architectures where it differs, an architecture-specific 'strong' version
+ * of this symbol is required.
+ *
+ * The default MMU page size is not affected by Transparent Huge Pages
+ * being in effect, or any usage of larger MMU page sizes (either through
+ * architectural huge-page mappings or other explicit/implicit coalescing of
+ * virtual ranges performed by the MMU).
+ *
+ * Return: The default MMU page size granularity for this VMA.
+ */
+__weak unsigned long vma_mmu_pagesize(struct vm_area_struct *vma)
+{
+	return vma_kernel_pagesize(vma);
+}