[PATCH V2 01/14] mm: Add read-write accessors for vm_page_prot
From: Anshuman Khandual <hidden>
Date: 2026-09-07 03:50:59
Also in:
linux-mm, lkml
Subsystem:
memory management, memory management - core, memory management - memory policy and migration, memory management - thp (transparent huge page), memory mapping, the rest · Maintainers:
Andrew Morton, David Hildenbrand, Liam R. Howlett, Lorenzo Stoakes, Linus Torvalds
Currently vma->vm_page_prot is safely read from and written to, without any locks with READ_ONCE() and WRITE_ONCE(). But with introduction of D128 page tables on arm64 platform, vm_page_prot grows to 128 bits which can't safely be handled with READ_ONCE() and WRITE_ONCE(). Add read and write accessors for vm_page_prot like pgprot_[read|write]() which any platform can override when required, although still defaulting as READ_ONCE() and WRITE_ONCE(), thus preserving the functionality for others. Cc: Andrew Morton <akpm@linux-foundation.org> Cc: David Hildenbrand <david@kernel.org> Cc: Lorenzo Stoakes <redacted> Cc: Mike Rapoport <rppt@kernel.org> Cc: linux-mm@kvack.org Cc: linux-kernel@vger.kernel.org Acked-by: Mike Rapoport (Microsoft) <rppt@kernel.org> Signed-off-by: Anshuman Khandual <redacted> --- include/linux/pgtable.h | 14 ++++++++++++++ mm/huge_memory.c | 4 ++-- mm/memory.c | 2 +- mm/migrate.c | 2 +- mm/mmap.c | 2 +- 5 files changed, 19 insertions(+), 5 deletions(-)
diff --git a/include/linux/pgtable.h b/include/linux/pgtable.h
index e3c8ab96941c..0df57a5c19ef 100644
--- a/include/linux/pgtable.h
+++ b/include/linux/pgtable.h@@ -524,6 +524,20 @@ static inline pgd_t pgdp_get(pgd_t *pgdp) } #endif +#ifndef pgprot_read +static inline pgprot_t pgprot_read(pgprot_t *prot) +{ + return READ_ONCE(*prot); +} +#endif + +#ifndef pgprot_write +static inline void pgprot_write(pgprot_t *prot, pgprot_t val) +{ + WRITE_ONCE(*prot, val); +} +#endif + #ifndef __HAVE_ARCH_PTEP_TEST_AND_CLEAR_YOUNG static inline bool ptep_test_and_clear_young(struct vm_area_struct *vma, unsigned long address, pte_t *ptep)
diff --git a/mm/huge_memory.c b/mm/huge_memory.c
index ced400f72d43..33753bffead4 100644
--- a/mm/huge_memory.c
+++ b/mm/huge_memory.c@@ -3391,7 +3391,7 @@ static void __split_huge_pmd_locked(struct vm_area_struct *vma, pmd_t *pmd, } else { pte_t entry; - entry = mk_pte(page, READ_ONCE(vma->vm_page_prot)); + entry = mk_pte(page, pgprot_read(&vma->vm_page_prot)); if (write) entry = pte_mkwrite(entry, vma); if (!young)
@@ -5103,7 +5103,7 @@ void remove_migration_pmd(struct page_vma_mapped_walk *pvmw, struct folio *folio entry = softleaf_from_pmd(*pvmw->pmd); folio_get(folio); - pmde = folio_mk_pmd(folio, READ_ONCE(vma->vm_page_prot)); + pmde = folio_mk_pmd(folio, pgprot_read(&vma->vm_page_prot)); if (pmd_swp_soft_dirty(*pvmw->pmd)) pmde = pmd_mksoft_dirty(pmde);
diff --git a/mm/memory.c b/mm/memory.c
index aa6b2fc770fc..fcea6098efb2 100644
--- a/mm/memory.c
+++ b/mm/memory.c@@ -939,7 +939,7 @@ static void restore_exclusive_pte(struct vm_area_struct *vma, VM_WARN_ON_FOLIO(!folio_test_locked(folio), folio); - pte = pte_mkold(mk_pte(page, READ_ONCE(vma->vm_page_prot))); + pte = pte_mkold(mk_pte(page, pgprot_read(&vma->vm_page_prot))); if (pte_swp_soft_dirty(orig_pte)) pte = pte_mksoft_dirty(pte);
diff --git a/mm/migrate.c b/mm/migrate.c
index 15b45832bcfa..579152cce502 100644
--- a/mm/migrate.c
+++ b/mm/migrate.c@@ -387,7 +387,7 @@ static bool remove_migration_pte(struct folio *folio, folio_get(folio); new = folio_page(folio, idx); - pte = mk_pte(new, READ_ONCE(vma->vm_page_prot)); + pte = mk_pte(new, pgprot_read(&vma->vm_page_prot)); if (!softleaf_is_migration_young(entry)) pte = pte_mkold(pte); if (folio_test_dirty(folio) && softleaf_is_migration_dirty(entry))
diff --git a/mm/mmap.c b/mm/mmap.c
index 4bf26b0f1e6e..729bc244b317 100644
--- a/mm/mmap.c
+++ b/mm/mmap.c@@ -89,7 +89,7 @@ void vma_set_page_prot(struct vm_area_struct *vma) vm_page_prot = vma_pgprot_modify(vm_page_prot, vma_flags); } /* remove_protection_ptes reads vma->vm_page_prot without mmap_lock */ - WRITE_ONCE(vma->vm_page_prot, vm_page_prot); + pgprot_write(&vma->vm_page_prot, vm_page_prot); } /*
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2.43.0