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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 05ea88608d ("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 c1d53b92b9
("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: c1d53b92b9 ("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>
master
David Hildenbrand (Arm) 2026-03-09 16:18:58 +01:00 committed by Andrew Morton
parent 1eba4c9599
commit 341ffe82a7
3 changed files with 20 additions and 24 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

7
include/linux/hugetlb.h
View File

@ -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;

20
include/linux/mm.h
View File

@ -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)
{

17
mm/hugetlb.c
View File

@ -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