mm: move vma_kernel_pagesize() from hugetlb to mm.h

Patch series "mm: move vma_(kernel|mmu)_pagesize() out of hugetlb.c", v2.

Looking into vma_(kernel|mmu)_pagesize(), I realized that there is one
scenario where DAX would not do the right thing when the kernel is not
compiled with hugetlb support.

Without hugetlb support, vma_(kernel|mmu)_pagesize() will always return
PAGE_SIZE instead of using the ->pagesize() result provided by dax-device
code.

Fix that by moving vma_kernel_pagesize() to core MM code, where it
belongs.  I don't think this is stable material, but am not 100% sure.

Also, move vma_mmu_pagesize() while at it.  Remove the unnecessary
hugetlb.h inclusion from KVM code.


This patch (of 4):

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.

Link: https://lkml.kernel.org/r/20260309151901.123947-1-david@kernel.org
Link: https://lkml.kernel.org/r/20260309151901.123947-2-david@kernel.org
Fixes: c1d53b92b95c ("device-dax: implement ->pagesize() for smaps to report MMUPageSize")
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: Dan Williams <dan.j.williams@intel.com>
Cc: "Christophe Leroy (CS GROUP)" <chleroy@kernel.org>
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, 20 insertions, 7 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 c758f4e68727..e62cea754b0e 100644
--- a/include/linux/mm.h
+++ b/include/linux/mm.h
@@ -1351,6 +1351,26 @@ 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)
 {