[PATCH v2 1/2] mm/mprotect: move softleaf code out of the main function

Pedro Falcato
2026-03-24T15:44:06Z

Move softleaf change_pte_range code into a separate function. This makes
the change_pte_range() function a good bit smaller, and lessens cognitive
load when reading through the function.

Reviewed-by: Lorenzo Stoakes (Oracle) <ljs@kernel.org>
Signed-off-by: Pedro Falcato <pfalcato@suse.de>
---
mm/mprotect.c | 129 +++++++++++++++++++++++++++-----------------------
1 file changed, 69 insertions(+), 60 deletions(-)

diff --git a/mm/mprotect.c b/mm/mprotect.c
index 9681f055b9fc..2eaf862e5734 100644
--- a/mm/mprotect.c
+++ b/mm/mprotect.c
@@ -211,6 +211,74 @@ 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 long change_softleaf_pte(struct vm_area_struct *vma,
+ unsigned long addr, pte_t *pte, pte_t oldpte, unsigned long cp_flags)
+{
+ const bool uffd_wp = cp_flags & MM_CP_UFFD_WP;
+ const 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;
+ /*
+ * 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;
+ }
+ return 0;
+ } 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;
+ }
+ 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 +385,7 @@ 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_softleaf_pte(vma, addr, pte, oldpte, cp_flags);
}
} while (pte += nr_ptes, addr += nr_ptes * PAGE_SIZE, addr != end);
lazy_mmu_mode_disable();
--
2.53.0