[PATCH V2 1/4] arm64/mm: Use pmdp_get() for PMD accesses
Anshuman Khandual
anshuman.khandual at arm.com
Wed Sep 23 04:01:43 PDT 2026
On Wed, Sep 23, 2026 at 09:32:17AM +0100, Ryan Roberts wrote:
> On 22/09/2026 07:16, Anshuman Khandual wrote:
> > Replace READ_ONCE() with pmdp_get() for PMD accesses in preparation for
> > supporting both D64 and D128 translation table formats.
> >
> > READ_ONCE() cannot currently be used for 128-bit page table entries on
> > arm64 because it does not provide the required 128-bit single-copy
> > atomicity, causing builds to fail for accesses wider than 64 bits.
> >
> > Although LDP/STP provide the required atomicity when FEAT_LSE is
> > available (as required by FEAT_D128), extending READ_ONCE() to support
> > 128-bit accesses is undesirable. READ_ONCE() is a general-purpose API,
> > so doing so could encourage other 128-bit users that would either fail
> > to build in configurations without D128 support or, if D128 becomes a
> > runtime option, silently permit tearing on systems without the required
> > hardware support.
> >
> > Instead, standardize PMD accesses on the existing page-table helpers.
> > These can be overridden on arm64 to provide 128-bit single-copy
> > atomicity when required. No functional change intended.
>
> I notice you have an unconverted READ_ONCE(*pmdp) in
> pmdp_test_and_clear_young(). Is that intentional?
Converting the above READ_ONCE() instances as pmdp_get() cuases a build
failure as pmpd_get() which is defined in generic pgtable header is not
visible inside platform specific pgtable header, even with a forward
declaration.
In D128 V2 series these conversions were performed later in the series,
when platform specific pxdp_get() overrides were added via ptval_get().
But to avoid this, we could just move pmdp_test_and_clear_young() inside
arch/arm64/mm/mmu.c file instead. Folding in the following change builds.
diff --git a/arch/arm64/include/asm/pgtable.h b/arch/arm64/include/asm/pgtable.h
index ae41946c54f26..13ca85ec89f6a 100644
--- a/arch/arm64/include/asm/pgtable.h
+++ b/arch/arm64/include/asm/pgtable.h
@@ -1289,14 +1289,8 @@ static inline bool __ptep_clear_flush_young(struct vm_area_struct *vma,
#if defined(CONFIG_TRANSPARENT_HUGEPAGE) || defined(CONFIG_ARCH_HAS_NONLEAF_PMD_YOUNG)
#define __HAVE_ARCH_PMDP_TEST_AND_CLEAR_YOUNG
-static inline bool pmdp_test_and_clear_young(struct vm_area_struct *vma,
- unsigned long address, pmd_t *pmdp)
-{
- /* Operation applies to PMD table entry only if FEAT_HAFT is enabled */
- VM_WARN_ON(pmd_table(READ_ONCE(*pmdp)) && !system_supports_haft());
- return __ptep_test_and_clear_young(vma, address, (pte_t *)pmdp);
-}
-#endif /* CONFIG_TRANSPARENT_HUGEPAGE || CONFIG_ARCH_HAS_NONLEAF_PMD_YOUNG */
+bool pmdp_test_and_clear_young(struct vm_area_struct *vma, unsigned long address, pmd_t *pmdp);
+#endif
static inline pte_t __ptep_get_and_clear_anysz(struct mm_struct *mm,
unsigned long address,
diff --git a/arch/arm64/mm/mmu.c b/arch/arm64/mm/mmu.c
index 76d8d320aeedf..b3fd06a623db5 100644
--- a/arch/arm64/mm/mmu.c
+++ b/arch/arm64/mm/mmu.c
@@ -2440,4 +2440,15 @@ void __check_safe_pte_update(struct mm_struct *mm, pte_t *ptep, pte_t pte)
__func__, pte_str_old, pte_str);
}
#endif /* CONFIG_DEBUG_VM */
+
+#if defined(CONFIG_TRANSPARENT_HUGEPAGE) || defined(CONFIG_ARCH_HAS_NONLEAF_PMD_YOUNG)
+#define __HAVE_ARCH_PMDP_TEST_AND_CLEAR_YOUNG
+bool pmdp_test_and_clear_young(struct vm_area_struct *vma, unsigned long address, pmd_t *pmdp)
+{
+ /* Operation applies to PMD table entry only if FEAT_HAFT is enabled */
+ VM_WARN_ON(pmd_table(pmdp_get(pmdp)) && !system_supports_haft());
+ return __ptep_test_and_clear_young(vma, address, (pte_t *)pmdp);
+}
+#endif /* CONFIG_TRANSPARENT_HUGEPAGE || CONFIG_ARCH_HAS_NONLEAF_PMD_YOUNG */
+
#endif
>
> Thanks,
> Ryan
>
>
> >
> > Cc: Catalin Marinas <catalin.marinas at arm.com>
> > Cc: Will Deacon <will at kernel.org>
> > Cc: Ryan Roberts <ryan.roberts at arm.com>
> > Cc: Mark Rtland <mark.rtland at arm.com>
> > Cc: linx-arm-kernel at lists.infradead.org
> > Cc: linx-kernel at vger.kernel.org
> > Cc: kasan-dev at googlegrops.com
> > Reviewed-by: Ryan Roberts <ryan.roberts at arm.com>
> > Signed-off-by: Anshuman Khandual <anshuman.khandual at arm.com>
> > ---
> > arch/arm64/include/asm/pgtable.h | 3 ++-
> > arch/arm64/mm/fault.c | 2 +-
> > arch/arm64/mm/fixmap.c | 2 +-
> > arch/arm64/mm/hugetlbpage.c | 2 +-
> > arch/arm64/mm/kasan_init.c | 4 ++--
> > arch/arm64/mm/mmu.c | 22 +++++++++++-----------
> > arch/arm64/mm/pageattr.c | 2 +-
> > arch/arm64/mm/trans_pgd.c | 2 +-
> > 8 files changed, 20 insertions(+), 19 deletions(-)
> >
> > diff --git a/arch/arm64/include/asm/pgtable.h b/arch/arm64/include/asm/pgtable.h
> > index 763c5a411d64..b953ea0ba3ed 100644
> > --- a/arch/arm64/include/asm/pgtable.h
> > +++ b/arch/arm64/include/asm/pgtable.h
> > @@ -811,7 +811,8 @@ static inline unsigned long pmd_page_vaddr(pmd_t pmd)
> > }
> >
> > /* Find an entry in the third-level page table. */
> > -#define pte_offset_phys(dir,addr) (pmd_page_paddr(READ_ONCE(*(dir))) + pte_index(addr) * sizeof(pte_t))
> > +#define pte_offset_phys(dir, addr) (pmd_page_paddr(pmdp_get(dir)) + \
> > + pte_index(addr) * sizeof(pte_t))
> >
> > #define pte_set_fixmap(addr) ((pte_t *)set_fixmap_offset(FIX_PTE, addr))
> > #define pte_set_fixmap_offset(pmd, addr) pte_set_fixmap(pte_offset_phys(pmd, addr))
> > diff --git a/arch/arm64/mm/fault.c b/arch/arm64/mm/fault.c
> > index 2cecf6ba6df7..2757ee0c4300 100644
> > --- a/arch/arm64/mm/fault.c
> > +++ b/arch/arm64/mm/fault.c
> > @@ -188,7 +188,7 @@ static void show_pte(unsigned long addr)
> > break;
> >
> > pmdp = pmd_offset_lockless(pudp, pud, addr);
> > - pmd = READ_ONCE(*pmdp);
> > + pmd = pmdp_get(pmdp);
> > ptval_to_str(pxd_str, pmd_val(pmd));
> > pr_cont(", pmd=%s", pxd_str);
> > if (pmd_none(pmd) || pmd_bad(pmd))
> > diff --git a/arch/arm64/mm/fixmap.c b/arch/arm64/mm/fixmap.c
> > index f66a0016dd02..3cdac8021d4f 100644
> > --- a/arch/arm64/mm/fixmap.c
> > +++ b/arch/arm64/mm/fixmap.c
> > @@ -42,7 +42,7 @@ static inline pte_t *fixmap_pte(unsigned long addr)
> >
> > static void __init early_fixmap_init_pte(pmd_t *pmdp, unsigned long addr)
> > {
> > - pmd_t pmd = READ_ONCE(*pmdp);
> > + pmd_t pmd = pmdp_get(pmdp);
> > pte_t *ptep;
> >
> > if (pmd_none(pmd)) {
> > diff --git a/arch/arm64/mm/hugetlbpage.c b/arch/arm64/mm/hugetlbpage.c
> > index 8e799c1fe0aa..cdaa4500faf9 100644
> > --- a/arch/arm64/mm/hugetlbpage.c
> > +++ b/arch/arm64/mm/hugetlbpage.c
> > @@ -304,7 +304,7 @@ pte_t *huge_pte_offset(struct mm_struct *mm,
> > addr &= CONT_PMD_MASK;
> >
> > pmdp = pmd_offset(pudp, addr);
> > - pmd = READ_ONCE(*pmdp);
> > + pmd = pmdp_get(pmdp);
> > if (!(sz == PMD_SIZE || sz == CONT_PMD_SIZE) &&
> > pmd_none(pmd))
> > return NULL;
> > diff --git a/arch/arm64/mm/kasan_init.c b/arch/arm64/mm/kasan_init.c
> > index 45fbdce684c8..7ca833c5de5e 100644
> > --- a/arch/arm64/mm/kasan_init.c
> > +++ b/arch/arm64/mm/kasan_init.c
> > @@ -62,7 +62,7 @@ static phys_addr_t __init kasan_alloc_raw_page(int node)
> > static pte_t *__init kasan_pte_offset(pmd_t *pmdp, unsigned long addr, int node,
> > bool early)
> > {
> > - if (pmd_none(READ_ONCE(*pmdp))) {
> > + if (pmd_none(pmdp_get(pmdp))) {
> > phys_addr_t pte_phys = early ?
> > __pa_symbol(kasan_early_shadow_pte)
> > : kasan_alloc_zeroed_page(node);
> > @@ -138,7 +138,7 @@ static void __init kasan_pmd_populate(pud_t *pudp, unsigned long addr,
> > do {
> > next = pmd_addr_end(addr, end);
> > kasan_pte_populate(pmdp, addr, next, node, early);
> > - } while (pmdp++, addr = next, addr != end && pmd_none(READ_ONCE(*pmdp)));
> > + } while (pmdp++, addr = next, addr != end && pmd_none(pmdp_get(pmdp)));
> > }
> >
> > static void __init kasan_pud_populate(p4d_t *p4dp, unsigned long addr,
> > diff --git a/arch/arm64/mm/mmu.c b/arch/arm64/mm/mmu.c
> > index e589fb00d1e3..95621913679e 100644
> > --- a/arch/arm64/mm/mmu.c
> > +++ b/arch/arm64/mm/mmu.c
> > @@ -200,7 +200,7 @@ static int alloc_init_cont_pte(pmd_t *pmdp, unsigned long addr,
> > int flags)
> > {
> > unsigned long next;
> > - pmd_t pmd = READ_ONCE(*pmdp);
> > + pmd_t pmd = pmdp_get(pmdp);
> > pte_t *ptep;
> >
> > BUG_ON(pmd_leaf(pmd));
> > @@ -257,7 +257,7 @@ static int init_pmd(pmd_t *pmdp, unsigned long addr, unsigned long end,
> > unsigned long next;
> >
> > do {
> > - pmd_t old_pmd = READ_ONCE(*pmdp);
> > + pmd_t old_pmd = pmdp_get(pmdp);
> >
> > next = pmd_addr_end(addr, end);
> >
> > @@ -272,7 +272,7 @@ static int init_pmd(pmd_t *pmdp, unsigned long addr, unsigned long end,
> > * only allow updates to the permission attributes.
> > */
> > BUG_ON(!pgattr_change_is_safe(pmd_val(old_pmd),
> > - READ_ONCE(pmd_val(*pmdp))));
> > + pmd_val(pmdp_get(pmdp))));
> > } else {
> > int ret;
> >
> > @@ -282,7 +282,7 @@ static int init_pmd(pmd_t *pmdp, unsigned long addr, unsigned long end,
> > return ret;
> >
> > VM_WARN_ON_ONCE(pmd_val(old_pmd) != 0 &&
> > - pmd_val(old_pmd) != READ_ONCE(pmd_val(*pmdp)));
> > + pmd_val(old_pmd) != pmd_val(pmdp_get(pmdp)));
> > }
> > phys += next - addr;
> > } while (pmdp++, addr = next, addr != end);
> > @@ -293,7 +293,7 @@ static int init_pmd(pmd_t *pmdp, unsigned long addr, unsigned long end,
> > static bool pmd_range_has_valid_noncont(pmd_t *pmdp)
> > {
> > for (int i = 0; i < CONT_PMDS; i++) {
> > - pte_t pte = pmd_pte(READ_ONCE(pmdp[i]));
> > + pte_t pte = pmd_pte(pmdp_get(pmdp + i));
> >
> > if (pte_valid(pte) && !pte_cont(pte))
> > return true;
> > @@ -1553,7 +1553,7 @@ static void unmap_hotplug_pmd_range(pud_t *pudp, unsigned long addr,
> > do {
> > next = pmd_addr_end(addr, end);
> > pmdp = pmd_offset(pudp, addr);
> > - pmd = READ_ONCE(*pmdp);
> > + pmd = pmdp_get(pmdp);
> > if (pmd_none(pmd))
> > continue;
> >
> > @@ -1708,7 +1708,7 @@ static void free_empty_pmd_table(pud_t *pudp, unsigned long addr,
> > do {
> > next = pmd_addr_end(addr, end);
> > pmdp = pmd_offset(pudp, addr);
> > - pmd = READ_ONCE(*pmdp);
> > + pmd = pmdp_get(pmdp);
> > if (pmd_none(pmd))
> > continue;
> >
> > @@ -1729,7 +1729,7 @@ static void free_empty_pmd_table(pud_t *pudp, unsigned long addr,
> > */
> > pmdp = pmd_offset(pudp, 0UL);
> > for (i = 0; i < PTRS_PER_PMD; i++) {
> > - if (!pmd_none(READ_ONCE(pmdp[i])))
> > + if (!pmd_none(pmdp_get(pmdp + i)))
> > return;
> > }
> >
> > @@ -1881,7 +1881,7 @@ int pmd_set_huge(pmd_t *pmdp, phys_addr_t phys, pgprot_t prot)
> > pmd_t new_pmd = pfn_pmd(__phys_to_pfn(phys), mk_pmd_sect_prot(prot));
> >
> > /* Only allow permission changes for now */
> > - if (!pgattr_change_is_safe(READ_ONCE(pmd_val(*pmdp)),
> > + if (!pgattr_change_is_safe(pmd_val(pmdp_get(pmdp)),
> > pmd_val(new_pmd)))
> > return 0;
> >
> > @@ -1906,7 +1906,7 @@ int pud_clear_huge(pud_t *pudp)
> >
> > int pmd_clear_huge(pmd_t *pmdp)
> > {
> > - if (!pmd_leaf(READ_ONCE(*pmdp)))
> > + if (!pmd_leaf(pmdp_get(pmdp)))
> > return 0;
> > pmd_clear(pmdp);
> > return 1;
> > @@ -1917,7 +1917,7 @@ int pmd_free_pte_page(pmd_t *pmdp, unsigned long addr)
> > pte_t *table;
> > pmd_t pmd;
> >
> > - pmd = READ_ONCE(*pmdp);
> > + pmd = pmdp_get(pmdp);
> >
> > if (!pmd_table(pmd)) {
> > VM_WARN_ON(1);
> > diff --git a/arch/arm64/mm/pageattr.c b/arch/arm64/mm/pageattr.c
> > index bbe98ac9ad8c..0ca07bd5ded9 100644
> > --- a/arch/arm64/mm/pageattr.c
> > +++ b/arch/arm64/mm/pageattr.c
> > @@ -414,7 +414,7 @@ bool kernel_page_present(struct page *page)
> > return pud_valid(pud);
> >
> > pmdp = pmd_offset(pudp, addr);
> > - pmd = READ_ONCE(*pmdp);
> > + pmd = pmdp_get(pmdp);
> > if (pmd_none(pmd))
> > return false;
> > if (pmd_leaf(pmd))
> > diff --git a/arch/arm64/mm/trans_pgd.c b/arch/arm64/mm/trans_pgd.c
> > index cca9706a875c..b27b2d2c20c3 100644
> > --- a/arch/arm64/mm/trans_pgd.c
> > +++ b/arch/arm64/mm/trans_pgd.c
> > @@ -74,7 +74,7 @@ static int copy_pmd(struct trans_pgd_info *info, pud_t *dst_pudp,
> >
> > src_pmdp = pmd_offset(src_pudp, start);
> > do {
> > - pmd_t pmd = READ_ONCE(*src_pmdp);
> > + pmd_t pmd = pmdp_get(src_pmdp);
> >
> > next = pmd_addr_end(addr, end);
> > if (pmd_none(pmd))
>
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