Re: [PATCH 03/16] mm: add vma_desc_size(), vma_desc_pages() helpers

David Hildenbrand
2025-09-08T15:10:28Z

On 08.09.25 13:10, Lorenzo Stoakes wrote:
> It's useful to be able to determine the size of a VMA descriptor range used
> on f_op->mmap_prepare, expressed both in bytes and pages, so add helpers
> for both and update code that could make use of it to do so.
>
> Signed-off-by: Lorenzo Stoakes <lorenzo.stoakes@oracle.com>
> ---
> fs/ntfs3/file.c | 2 +-
> include/linux/mm.h | 10 ++++++++++
> mm/secretmem.c | 2 +-
> 3 files changed, 12 insertions(+), 2 deletions(-)
>
> diff --git a/fs/ntfs3/file.c b/fs/ntfs3/file.c
> index c1ece707b195..86eb88f62714 100644
> --- a/fs/ntfs3/file.c
> +++ b/fs/ntfs3/file.c
> @@ -304,7 +304,7 @@ static int ntfs_file_mmap_prepare(struct vm_area_desc *desc)
>
> if (rw) {
> u64 to = min_t(loff_t, i_size_read(inode),
> - from + desc->end - desc->start);
> + from + vma_desc_size(desc));
>
> if (is_sparsed(ni)) {
> /* Allocate clusters for rw map. */
> diff --git a/include/linux/mm.h b/include/linux/mm.h
> index a6bfa46937a8..9d4508b20be3 100644
> --- a/include/linux/mm.h
> +++ b/include/linux/mm.h
> @@ -3560,6 +3560,16 @@ static inline unsigned long vma_pages(const struct vm_area_struct *vma)
> return (vma->vm_end - vma->vm_start) >> PAGE_SHIFT;
> }
>
> +static inline unsigned long vma_desc_size(struct vm_area_desc *desc)
> +{
> + return desc->end - desc->start;
> +}
> +
> +static inline unsigned long vma_desc_pages(struct vm_area_desc *desc)
> +{
> + return vma_desc_size(desc) >> PAGE_SHIFT;
> +}

"const struct vm_area_desc *" in both cases?

> +
> /* Look up the first VMA which exactly match the interval vm_start ... vm_end */
> static inline struct vm_area_struct *find_exact_vma(struct mm_struct *mm,
> unsigned long vm_start, unsigned long vm_end)
> diff --git a/mm/secretmem.c b/mm/secretmem.c
> index 60137305bc20..62066ddb1e9c 100644
> --- a/mm/secretmem.c
> +++ b/mm/secretmem.c
> @@ -120,7 +120,7 @@ static int secretmem_release(struct inode *inode, struct file *file)
>
> static int secretmem_mmap_prepare(struct vm_area_desc *desc)
> {
> - const unsigned long len = desc->end - desc->start;
> + const unsigned long len = vma_desc_size(desc);
>
> if ((desc->vm_flags & (VM_SHARED | VM_MAYSHARE)) == 0)
> return -EINVAL;

We really want to forbid any private mappings here, independent of cow.

Maybe a is_private_mapping() helper

or a

vma_desc_is_private_mapping()

helper if we really need it

--
Cheers

David / dhildenb