Re: [RFC PATCH v2 3/4] mm: add functions folio_in_range() and folio_within_vma()

[Yu Zhao]

On Fri, Jul 21, 2023 at 3:41 AM Yin Fengwei <fengwei.yin@xxxxxxxxx> wrote:
>
> It will be used to check whether the folio is mapped to specific
> VMA and whether the mapping address of folio is in the range.
>
> Also a helper function folio_within_vma() to check whether folio
> is in the range of vma based on folio_in_range().
>
> Signed-off-by: Yin Fengwei <fengwei.yin@xxxxxxxxx>
> ---
>  mm/internal.h | 32 ++++++++++++++++++++++++++++++++
>  1 file changed, 32 insertions(+)
>
> diff --git a/mm/internal.h b/mm/internal.h
> index 483add0bfb28..c7dd15d8de3e 100644
> --- a/mm/internal.h
> +++ b/mm/internal.h
> @@ -585,6 +585,38 @@ extern long faultin_vma_page_range(struct vm_area_struct *vma,
>                                    bool write, int *locked);
>  extern bool mlock_future_ok(struct mm_struct *mm, unsigned long flags,
>                                unsigned long bytes);
> +
> +static inline bool
> +folio_in_range(struct folio *folio, struct vm_area_struct *vma,
> +               unsigned long start, unsigned long end)
> +{
> +       pgoff_t pgoff, addr;
> +       unsigned long vma_pglen = (vma->vm_end - vma->vm_start) >> PAGE_SHIFT;
> +
> +       VM_WARN_ON_FOLIO(folio_test_ksm(folio), folio);
> +       if (start < vma->vm_start)
> +               start = vma->vm_start;
> +
> +       if (end > vma->vm_end)
> +               end = vma->vm_end;
> +
> +       pgoff = folio_pgoff(folio);
> +
> +       /* if folio start address is not in vma range */
> +       if (pgoff < vma->vm_pgoff || pgoff > vma->vm_pgoff + vma_pglen)
> +               return false;
> +
> +       addr = vma->vm_start + ((pgoff - vma->vm_pgoff) << PAGE_SHIFT);
> +
> +       return ((addr >= start) && (addr + folio_size(folio) <= end));

Not sure how much we care but better to avoid (addr + folio_size()),
since it might wrap to 0 on 32-bit systems.

Reusing some helpers from mm/internal.h, e.g., vma_pgoff_address(),
would be great, if it's possible (I'm not sure if it's).