From: Anshuman Khandual <anshuman.khandual@arm.com>
To: linux-arm-kernel@lists.infradead.org, catalin.marinas@arm.com,
will@kernel.org
Cc: Anshuman Khandual <anshuman.khandual@arm.com>,
Ryan Roberts <ryan.roberts@arm.com>,
Mark Rutland <mark.rutland@arm.com>,
Lorenzo Stoakes <ljs@kernel.org>,
Andrew Morton <akpm@linux-foundation.org>,
David Hildenbrand <david@kernel.org>,
Mike Rapoport <rppt@kernel.org>,
Linu Cherian <linu.cherian@arm.com>,
linux-kernel@vger.kernel.org, linux-mm@kvack.org,
kasan-dev@googlegroups.com
Subject: [PATCH V4 1/4] arm64/mm: Use pmdp_get() for PMD accesses
Date: Thu, 5 Nov 2026 10:04:00 +0530 [thread overview]
Message-ID: <20261105043403.3326445-2-anshuman.khandual@arm.com> (raw)
In-Reply-To: <20261105043403.3326445-1-anshuman.khandual@arm.com>
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.
READ_ONCE() instance in pmdp_test_and_clear_young() could not be converted
into pmpd_get() because of cyclic dependency between <linux/pgtable.h> and
<asm/pgtable.h>. Move the function inside <arch/arm64/mm/mmu.c> instead to
workaround the problem.
No functional change intended.
Cc: Catalin Marinas <catalin.marinas@arm.com>
Cc: Will Deacon <will@kernel.org>
Cc: Ryan Roberts <ryan.roberts@arm.com>
Cc: Mark Rutland <mark.rutland@arm.com>
Cc: linux-arm-kernel@lists.infradead.org
Cc: linux-kernel@vger.kernel.org
Cc: kasan-dev@googlegroups.com
Reviewed-by: Ryan Roberts <ryan.roberts@arm.com>
Signed-off-by: Anshuman Khandual <anshuman.khandual@arm.com>
---
Changes in V4:
- Dropped pmdp_get() platform override
- Moved pmdp_test_and_clear_young() inside arch/arm64/mm/mmu.c
arch/arm64/include/asm/pgtable.h | 11 +++--------
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 | 31 ++++++++++++++++++++-----------
arch/arm64/mm/pageattr.c | 2 +-
arch/arm64/mm/trans_pgd.c | 2 +-
8 files changed, 30 insertions(+), 26 deletions(-)
diff --git a/arch/arm64/include/asm/pgtable.h b/arch/arm64/include/asm/pgtable.h
index a474c9fb485a..f619fa74da3c 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))
@@ -1287,13 +1288,7 @@ 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);
-}
+bool pmdp_test_and_clear_young(struct vm_area_struct *vma, unsigned long address, pmd_t *pmdp);
#endif /* CONFIG_TRANSPARENT_HUGEPAGE || CONFIG_ARCH_HAS_NONLEAF_PMD_YOUNG */
static inline pte_t __ptep_get_and_clear_anysz(struct mm_struct *mm,
diff --git a/arch/arm64/mm/fault.c b/arch/arm64/mm/fault.c
index b22736853fcd..33b05a9f13d7 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 140520b351e2..c998310406f9 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);
@@ -2441,3 +2441,12 @@ 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)
+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 */
diff --git a/arch/arm64/mm/pageattr.c b/arch/arm64/mm/pageattr.c
index de7bf95003ea..bf1fd1258a75 100644
--- a/arch/arm64/mm/pageattr.c
+++ b/arch/arm64/mm/pageattr.c
@@ -362,7 +362,7 @@ 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))
--
2.43.0
next prev parent reply other threads:[~2026-11-05 4:34 UTC|newest]
Thread overview: 5+ messages / expand[flat|nested] mbox.gz Atom feed top
2026-11-05 4:33 [PATCH V4 0/4] arm64/mm: Convert pgtable READ_ONCE() as pxdp_get() Anshuman Khandual
2026-11-05 4:34 ` Anshuman Khandual [this message]
2026-11-05 4:34 ` [PATCH V4 2/4] arm64/mm: Use pudp_get() for PUD accesses Anshuman Khandual
2026-11-05 4:34 ` [PATCH V4 3/4] arm64/mm: Use p4dp_get() for P4D accesses Anshuman Khandual
2026-11-05 4:34 ` [PATCH V4 4/4] arm64/mm: Use pgdp_get() for PGD accesses Anshuman Khandual
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