Re: [PATCH 1/6] mm/gup: move gup_can_follow_protnone() to gup.c

["Lorenzo Stoakes (ARM)" <ljs@kernel.org>]

On Sun, Aug 23, 2026 at 03:17:38PM +0300, Mike Rapoport (Microsoft) wrote:
> gup_can_follow_protnone() is defined in include/linux/mm.h but only used
> by mm/gup.c.
>
> First, there is no reason to have it in already gigantic header.
>
> Next, the upcoming refactoring of userfaultfd flags will make
> gup_can_follow_protnone() depend on userfaultfd_k.h which would cause a
> cyclic header dependency.
>
> Move gup_can_follow_protnone() to mm/gup.c.
>
> No functional change.
>
> Assisted-by: copilot:claude-opus-5
> Signed-off-by: Mike Rapoport (Microsoft) <rppt@kernel.org>

LGTM so:

Reviewed-by: Lorenzo Stoakes (ARM) <ljs@kernel.org>

> ---
>  include/linux/mm.h | 38 --------------------------------------
>  mm/gup.c           | 38 ++++++++++++++++++++++++++++++++++++++
>  2 files changed, 38 insertions(+), 38 deletions(-)
>
> diff --git a/include/linux/mm.h b/include/linux/mm.h
> index 0829e0d3b2d1..4daf9cd6ae8e 100644
> --- a/include/linux/mm.h
> +++ b/include/linux/mm.h
> @@ -4860,44 +4860,6 @@ static inline int vm_fault_to_errno(vm_fault_t vm_fault, int foll_flags)
>  	return 0;
>  }
>
> -/*
> - * Indicates whether GUP can follow a PROT_NONE mapped page, or whether
> - * a (NUMA hinting or userfaultfd RWP) fault is required.
> - */
> -static inline bool gup_can_follow_protnone(const struct vm_area_struct *vma,
> -					   unsigned int flags)
> -{
> -	/*
> -	 * VM_UFFD_RWP uses protnone as an access-tracking marker, not for
> -	 * NUMA hinting. GUP must always take a fault so the access is
> -	 * delivered to userfaultfd, regardless of FOLL_HONOR_NUMA_FAULT.
> -	 *
> -	 * Only do so while the VMA is accessible. If it has been made
> -	 * inaccessible (e.g. mprotect(PROT_NONE)), fall through to the guard
> -	 * below: forcing a fault there would loop, as handle_mm_fault() makes
> -	 * no progress on protnone in an inaccessible VMA, and the access is
> -	 * denied regardless of RWP anyway.
> -	 */
> -	if (vma_test_single_mask(vma, VMA_UFFD_RWP) && vma_is_accessible(vma))
> -		return false;
> -
> -	/*
> -	 * If callers don't want to honor NUMA hinting faults, no need to
> -	 * determine if we would actually have to trigger a NUMA hinting fault.
> -	 */
> -	if (!(flags & FOLL_HONOR_NUMA_FAULT))
> -		return true;
> -
> -	/*
> -	 * NUMA hinting faults don't apply in inaccessible (PROT_NONE) VMAs.
> -	 *
> -	 * Requiring a fault here even for inaccessible VMAs would mean that
> -	 * FOLL_FORCE cannot make any progress, because handle_mm_fault()
> -	 * refuses to process NUMA hinting faults in inaccessible VMAs.
> -	 */
> -	return !vma_is_accessible(vma);
> -}
> -
>  typedef int (*pte_fn_t)(pte_t *pte, unsigned long addr, void *data);
>  extern int apply_to_page_range(struct mm_struct *mm, unsigned long address,
>  			       unsigned long size, pte_fn_t fn, void *data);
> diff --git a/mm/gup.c b/mm/gup.c
> index eb898ea1ee22..500e2aa99e48 100644
> --- a/mm/gup.c
> +++ b/mm/gup.c
> @@ -633,6 +633,44 @@ static struct page *no_page_table(struct vm_area_struct *vma,
>  	return NULL;
>  }
>
> +/*
> + * Indicates whether GUP can follow a PROT_NONE mapped page, or whether
> + * a (NUMA hinting or userfaultfd RWP) fault is required.
> + */
> +static inline bool gup_can_follow_protnone(const struct vm_area_struct *vma,
> +					   unsigned int flags)
> +{
> +	/*
> +	 * VM_UFFD_RWP uses protnone as an access-tracking marker, not for
> +	 * NUMA hinting. GUP must always take a fault so the access is
> +	 * delivered to userfaultfd, regardless of FOLL_HONOR_NUMA_FAULT.
> +	 *
> +	 * Only do so while the VMA is accessible. If it has been made
> +	 * inaccessible (e.g. mprotect(PROT_NONE)), fall through to the guard
> +	 * below: forcing a fault there would loop, as handle_mm_fault() makes
> +	 * no progress on protnone in an inaccessible VMA, and the access is
> +	 * denied regardless of RWP anyway.
> +	 */
> +	if (vma_test_single_mask(vma, VMA_UFFD_RWP) && vma_is_accessible(vma))
> +		return false;
> +
> +	/*
> +	 * If callers don't want to honor NUMA hinting faults, no need to
> +	 * determine if we would actually have to trigger a NUMA hinting fault.
> +	 */
> +	if (!(flags & FOLL_HONOR_NUMA_FAULT))
> +		return true;
> +
> +	/*
> +	 * NUMA hinting faults don't apply in inaccessible (PROT_NONE) VMAs.
> +	 *
> +	 * Requiring a fault here even for inaccessible VMAs would mean that
> +	 * FOLL_FORCE cannot make any progress, because handle_mm_fault()
> +	 * refuses to process NUMA hinting faults in inaccessible VMAs.
> +	 */
> +	return !vma_is_accessible(vma);
> +}
> +
>  #ifdef CONFIG_PGTABLE_HAS_HUGE_LEAVES
>  /* FOLL_FORCE can write to even unwritable PUDs in COW mappings. */
>  static inline bool can_follow_write_pud(pud_t pud, struct page *page,
>
> --
> 2.53.0
>

--
Cheers, Lorenzo