Re: [PATCH 2/4] mm/mprotect: move softleaf code out of the main function

[Lorenzo Stoakes (Oracle)]

On Thu, Mar 19, 2026 at 06:31:06PM +0000, Pedro Falcato wrote:
> Move softleaf change_pte_range code into a separate function. This makes
> the change_pte_range() function (or where it inlines) a good bit
> smaller. Plus it lessens cognitive load when reading through the
> function.
>
> Signed-off-by: Pedro Falcato <pfalcato@xxxxxxx>

Honestly I like this as a refactoring, the noinline notwithstanding, so:

Reviewed-by: Lorenzo Stoakes (Oracle) <ljs@xxxxxxxxxx>

> ---
>  mm/mprotect.c | 128 +++++++++++++++++++++++++++-----------------------
>  1 file changed, 68 insertions(+), 60 deletions(-)
>
> diff --git a/mm/mprotect.c b/mm/mprotect.c
> index 1bd0d4aa07c2..8d4fa38a8a26 100644
> --- a/mm/mprotect.c
> +++ b/mm/mprotect.c
> @@ -211,6 +211,73 @@ static void set_write_prot_commit_flush_ptes(struct vm_area_struct *vma,
>  	commit_anon_folio_batch(vma, folio, page, addr, ptep, oldpte, ptent, nr_ptes, tlb);
>  }
>
> +static noinline long change_pte_softleaf(struct vm_area_struct *vma,
> +	unsigned long addr, pte_t *pte, pte_t oldpte, unsigned long cp_flags)
> +{
> +	bool uffd_wp = cp_flags & MM_CP_UFFD_WP;
> +	bool uffd_wp_resolve = cp_flags & MM_CP_UFFD_WP_RESOLVE;
> +	softleaf_t entry = softleaf_from_pte(oldpte);
> +	pte_t newpte;
> +
> +	if (softleaf_is_migration_write(entry)) {
> +		const struct folio *folio = softleaf_to_folio(entry);
> +
> +		/*
> +		 * A protection check is difficult so
> +		 * just be safe and disable write
> +		 */
> +		if (folio_test_anon(folio))
> +			entry = make_readable_exclusive_migration_entry(
> +					     swp_offset(entry));
> +		else
> +			entry = make_readable_migration_entry(swp_offset(entry));
> +		newpte = swp_entry_to_pte(entry);
> +		if (pte_swp_soft_dirty(oldpte))
> +			newpte = pte_swp_mksoft_dirty(newpte);
> +	} else if (softleaf_is_device_private_write(entry)) {
> +		/*
> +		 * We do not preserve soft-dirtiness. See
> +		 * copy_nonpresent_pte() for explanation.
> +		 */
> +		entry = make_readable_device_private_entry(
> +					swp_offset(entry));
> +		newpte = swp_entry_to_pte(entry);
> +		if (pte_swp_uffd_wp(oldpte))
> +			newpte = pte_swp_mkuffd_wp(newpte);
> +	} else if (softleaf_is_marker(entry)) {
> +		/*
> +		 * Ignore error swap entries unconditionally,
> +		 * because any access should sigbus/sigsegv
> +		 * anyway.
> +		 */
> +		if (softleaf_is_poison_marker(entry) ||
> +		    softleaf_is_guard_marker(entry))
> +			return 0;

This just continues in the original:

				if (softleaf_is_poison_marker(entry) ||
				    softleaf_is_guard_marker(entry))
					continue;
So this is correct.


> +		/*
> +		 * If this is uffd-wp pte marker and we'd like
> +		 * to unprotect it, drop it; the next page
> +		 * fault will trigger without uffd trapping.
> +		 */
> +		if (uffd_wp_resolve) {
> +			pte_clear(vma->vm_mm, addr, pte);
> +			return 1;

This incrmements pages and continues in the orignal:

				if (uffd_wp_resolve) {
					pte_clear(vma->vm_mm, addr, pte);
					pages++;
				}
				continue;

So this is correct.

> +		}
> +	} else {
> +		newpte = oldpte;
> +	}
> +
> +	if (uffd_wp)
> +		newpte = pte_swp_mkuffd_wp(newpte);
> +	else if (uffd_wp_resolve)
> +		newpte = pte_swp_clear_uffd_wp(newpte);
> +
> +	if (!pte_same(oldpte, newpte)) {
> +		set_pte_at(vma->vm_mm, addr, pte, newpte);
> +		return 1;

This increments pages and is at the end of the loop in the original:

			if (!pte_same(oldpte, newpte)) {
				set_pte_at(vma->vm_mm, addr, pte, newpte);
				pages++;
			}

So this is correct.

> +	}
> +	return 0;
> +}
> +
>  static long change_pte_range(struct mmu_gather *tlb,
>  		struct vm_area_struct *vma, pmd_t *pmd, unsigned long addr,
>  		unsigned long end, pgprot_t newprot, unsigned long cp_flags)
> @@ -317,66 +384,7 @@ static long change_pte_range(struct mmu_gather *tlb,
>  				pages++;
>  			}
>  		} else  {
> -			softleaf_t entry = softleaf_from_pte(oldpte);
> -			pte_t newpte;
> -
> -			if (softleaf_is_migration_write(entry)) {
> -				const struct folio *folio = softleaf_to_folio(entry);
> -
> -				/*
> -				 * A protection check is difficult so
> -				 * just be safe and disable write
> -				 */
> -				if (folio_test_anon(folio))
> -					entry = make_readable_exclusive_migration_entry(
> -							     swp_offset(entry));
> -				else
> -					entry = make_readable_migration_entry(swp_offset(entry));
> -				newpte = swp_entry_to_pte(entry);
> -				if (pte_swp_soft_dirty(oldpte))
> -					newpte = pte_swp_mksoft_dirty(newpte);
> -			} else if (softleaf_is_device_private_write(entry)) {
> -				/*
> -				 * We do not preserve soft-dirtiness. See
> -				 * copy_nonpresent_pte() for explanation.
> -				 */
> -				entry = make_readable_device_private_entry(
> -							swp_offset(entry));
> -				newpte = swp_entry_to_pte(entry);
> -				if (pte_swp_uffd_wp(oldpte))
> -					newpte = pte_swp_mkuffd_wp(newpte);
> -			} else if (softleaf_is_marker(entry)) {
> -				/*
> -				 * Ignore error swap entries unconditionally,
> -				 * because any access should sigbus/sigsegv
> -				 * anyway.
> -				 */
> -				if (softleaf_is_poison_marker(entry) ||
> -				    softleaf_is_guard_marker(entry))
> -					continue;
> -				/*
> -				 * If this is uffd-wp pte marker and we'd like
> -				 * to unprotect it, drop it; the next page
> -				 * fault will trigger without uffd trapping.
> -				 */
> -				if (uffd_wp_resolve) {
> -					pte_clear(vma->vm_mm, addr, pte);
> -					pages++;
> -				}
> -				continue;
> -			} else {
> -				newpte = oldpte;
> -			}
> -
> -			if (uffd_wp)
> -				newpte = pte_swp_mkuffd_wp(newpte);
> -			else if (uffd_wp_resolve)
> -				newpte = pte_swp_clear_uffd_wp(newpte);
> -
> -			if (!pte_same(oldpte, newpte)) {
> -				set_pte_at(vma->vm_mm, addr, pte, newpte);
> -				pages++;
> -			}
> +			pages += change_pte_softleaf(vma, addr, pte, oldpte, cp_flags);
>  		}
>  	} while (pte += nr_ptes, addr += nr_ptes * PAGE_SIZE, addr != end);
>  	lazy_mmu_mode_disable();
> --
> 2.53.0
>