From: Anshuman Khandual <anshuman.khandual@arm.com>
To: linux-arm-kernel@lists.infradead.org
Cc: Anshuman Khandual <anshuman.khandual@arm.com>,
Catalin Marinas <catalin.marinas@arm.com>,
Will Deacon <will@kernel.org>,
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 V2 2/4] arm64/mm: Use pudp_get() for PUD accesses
Date: Tue, 22 Sep 2026 11:46:36 +0530 [thread overview]
Message-ID: <20260922061638.3967467-3-anshuman.khandual@arm.com> (raw)
In-Reply-To: <20260922061638.3967467-1-anshuman.khandual@arm.com>
Replace READ_ONCE() with pudp_get() for PUD 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 PUD 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.
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
Signed-off-by: Anshuman Khandual <anshuman.khandual@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 | 4 ++--
arch/arm64/mm/kasan_init.c | 4 ++--
arch/arm64/mm/mmu.c | 20 ++++++++++----------
arch/arm64/mm/pageattr.c | 2 +-
arch/arm64/mm/trans_pgd.c | 4 ++--
8 files changed, 21 insertions(+), 20 deletions(-)
diff --git a/arch/arm64/include/asm/pgtable.h b/arch/arm64/include/asm/pgtable.h
index b953ea0ba3ed..ae41946c54f2 100644
--- a/arch/arm64/include/asm/pgtable.h
+++ b/arch/arm64/include/asm/pgtable.h
@@ -873,7 +873,8 @@ static inline pmd_t *pud_pgtable(pud_t pud)
}
/* Find an entry in the second-level page table. */
-#define pmd_offset_phys(dir, addr) (pud_page_paddr(READ_ONCE(*(dir))) + pmd_index(addr) * sizeof(pmd_t))
+#define pmd_offset_phys(dir, addr) (pud_page_paddr(pudp_get(dir)) + \
+ pmd_index(addr) * sizeof(pmd_t))
#define pmd_set_fixmap(addr) ((pmd_t *)set_fixmap_offset(FIX_PMD, addr))
#define pmd_set_fixmap_offset(pud, addr) pmd_set_fixmap(pmd_offset_phys(pud, addr))
diff --git a/arch/arm64/mm/fault.c b/arch/arm64/mm/fault.c
index 2757ee0c4300..435e2e14c070 100644
--- a/arch/arm64/mm/fault.c
+++ b/arch/arm64/mm/fault.c
@@ -181,7 +181,7 @@ static void show_pte(unsigned long addr)
break;
pudp = pud_offset_lockless(p4dp, p4d, addr);
- pud = READ_ONCE(*pudp);
+ pud = pudp_get(pudp);
ptval_to_str(pxd_str, pud_val(pud));
pr_cont(", pud=%s", pxd_str);
if (pud_none(pud) || pud_bad(pud))
diff --git a/arch/arm64/mm/fixmap.c b/arch/arm64/mm/fixmap.c
index 3cdac8021d4f..d9a870836faf 100644
--- a/arch/arm64/mm/fixmap.c
+++ b/arch/arm64/mm/fixmap.c
@@ -56,7 +56,7 @@ static void __init early_fixmap_init_pmd(pud_t *pudp, unsigned long addr,
unsigned long end)
{
unsigned long next;
- pud_t pud = READ_ONCE(*pudp);
+ pud_t pud = pudp_get(pudp);
pmd_t *pmdp;
if (pud_none(pud))
diff --git a/arch/arm64/mm/hugetlbpage.c b/arch/arm64/mm/hugetlbpage.c
index cdaa4500faf9..c9ad5e75b073 100644
--- a/arch/arm64/mm/hugetlbpage.c
+++ b/arch/arm64/mm/hugetlbpage.c
@@ -262,7 +262,7 @@ pte_t *huge_pte_alloc(struct mm_struct *mm, struct vm_area_struct *vma,
WARN_ON(addr & (sz - 1));
ptep = pte_alloc_huge(mm, pmdp, addr);
} else if (sz == PMD_SIZE) {
- if (want_pmd_share(vma, addr) && pud_none(READ_ONCE(*pudp)))
+ if (want_pmd_share(vma, addr) && pud_none(pudp_get(pudp)))
ptep = huge_pmd_share(mm, vma, addr, pudp);
else
ptep = (pte_t *)pmd_alloc(mm, pudp, addr);
@@ -292,7 +292,7 @@ pte_t *huge_pte_offset(struct mm_struct *mm,
return NULL;
pudp = pud_offset(p4dp, addr);
- pud = READ_ONCE(*pudp);
+ pud = pudp_get(pudp);
if (sz != PUD_SIZE && pud_none(pud))
return NULL;
/* hugepage or swap? */
diff --git a/arch/arm64/mm/kasan_init.c b/arch/arm64/mm/kasan_init.c
index 7ca833c5de5e..aad29bcc7622 100644
--- a/arch/arm64/mm/kasan_init.c
+++ b/arch/arm64/mm/kasan_init.c
@@ -76,7 +76,7 @@ static pte_t *__init kasan_pte_offset(pmd_t *pmdp, unsigned long addr, int node,
static pmd_t *__init kasan_pmd_offset(pud_t *pudp, unsigned long addr, int node,
bool early)
{
- if (pud_none(READ_ONCE(*pudp))) {
+ if (pud_none(pudp_get(pudp))) {
phys_addr_t pmd_phys = early ?
__pa_symbol(kasan_early_shadow_pmd)
: kasan_alloc_zeroed_page(node);
@@ -150,7 +150,7 @@ static void __init kasan_pud_populate(p4d_t *p4dp, unsigned long addr,
do {
next = pud_addr_end(addr, end);
kasan_pmd_populate(pudp, addr, next, node, early);
- } while (pudp++, addr = next, addr != end && pud_none(READ_ONCE(*pudp)));
+ } while (pudp++, addr = next, addr != end && pud_none(pudp_get(pudp)));
}
static void __init kasan_p4d_populate(pgd_t *pgdp, unsigned long addr,
diff --git a/arch/arm64/mm/mmu.c b/arch/arm64/mm/mmu.c
index 95621913679e..22efaee79293 100644
--- a/arch/arm64/mm/mmu.c
+++ b/arch/arm64/mm/mmu.c
@@ -309,7 +309,7 @@ static int alloc_init_cont_pmd(pud_t *pudp, unsigned long addr,
{
int ret;
unsigned long next;
- pud_t pud = READ_ONCE(*pudp);
+ pud_t pud = pudp_get(pudp);
pmd_t *pmdp;
/*
@@ -390,7 +390,7 @@ static int alloc_init_pud(p4d_t *p4dp, unsigned long addr, unsigned long end,
}
do {
- pud_t old_pud = READ_ONCE(*pudp);
+ pud_t old_pud = pudp_get(pudp);
next = pud_addr_end(addr, end);
@@ -408,7 +408,7 @@ static int alloc_init_pud(p4d_t *p4dp, unsigned long addr, unsigned long end,
* only allow updates to the permission attributes.
*/
BUG_ON(!pgattr_change_is_safe(pud_val(old_pud),
- READ_ONCE(pud_val(*pudp))));
+ pud_val(pudp_get(pudp))));
} else {
ret = alloc_init_cont_pmd(pudp, addr, next, phys, prot,
pgtable_alloc, flags);
@@ -416,7 +416,7 @@ static int alloc_init_pud(p4d_t *p4dp, unsigned long addr, unsigned long end,
goto out;
VM_WARN_ON_ONCE(pud_val(old_pud) != 0 &&
- pud_val(old_pud) != READ_ONCE(pud_val(*pudp)));
+ pud_val(old_pud) != pud_val(pudp_get(pudp)));
}
phys += next - addr;
} while (pudp++, addr = next, addr != end);
@@ -1591,7 +1591,7 @@ static void unmap_hotplug_pud_range(p4d_t *p4dp, unsigned long addr,
do {
next = pud_addr_end(addr, end);
pudp = pud_offset(p4dp, addr);
- pud = READ_ONCE(*pudp);
+ pud = pudp_get(pudp);
if (pud_none(pud))
continue;
@@ -1748,7 +1748,7 @@ static void free_empty_pud_table(p4d_t *p4dp, unsigned long addr,
do {
next = pud_addr_end(addr, end);
pudp = pud_offset(p4dp, addr);
- pud = READ_ONCE(*pudp);
+ pud = pudp_get(pudp);
if (pud_none(pud))
continue;
@@ -1769,7 +1769,7 @@ static void free_empty_pud_table(p4d_t *p4dp, unsigned long addr,
*/
pudp = pud_offset(p4dp, 0UL);
for (i = 0; i < PTRS_PER_PUD; i++) {
- if (!pud_none(READ_ONCE(pudp[i])))
+ if (!pud_none(pudp_get(pudp + i)))
return;
}
@@ -1867,7 +1867,7 @@ int pud_set_huge(pud_t *pudp, phys_addr_t phys, pgprot_t prot)
pud_t new_pud = pfn_pud(__phys_to_pfn(phys), mk_pud_sect_prot(prot));
/* Only allow permission changes for now */
- if (!pgattr_change_is_safe(READ_ONCE(pud_val(*pudp)),
+ if (!pgattr_change_is_safe(pud_val(pudp_get(pudp)),
pud_val(new_pud)))
return 0;
@@ -1898,7 +1898,7 @@ void p4d_clear_huge(p4d_t *p4dp)
int pud_clear_huge(pud_t *pudp)
{
- if (!pud_leaf(READ_ONCE(*pudp)))
+ if (!pud_leaf(pudp_get(pudp)))
return 0;
pud_clear(pudp);
return 1;
@@ -1938,7 +1938,7 @@ int pud_free_pmd_page(pud_t *pudp, unsigned long addr)
pud_t pud;
unsigned long next, end;
- pud = READ_ONCE(*pudp);
+ pud = pudp_get(pudp);
if (!pud_table(pud)) {
VM_WARN_ON(1);
diff --git a/arch/arm64/mm/pageattr.c b/arch/arm64/mm/pageattr.c
index 0ca07bd5ded9..07b2fa4de57f 100644
--- a/arch/arm64/mm/pageattr.c
+++ b/arch/arm64/mm/pageattr.c
@@ -407,7 +407,7 @@ bool kernel_page_present(struct page *page)
return false;
pudp = pud_offset(p4dp, addr);
- pud = READ_ONCE(*pudp);
+ pud = pudp_get(pudp);
if (pud_none(pud))
return false;
if (pud_leaf(pud))
diff --git a/arch/arm64/mm/trans_pgd.c b/arch/arm64/mm/trans_pgd.c
index b27b2d2c20c3..d119119455f1 100644
--- a/arch/arm64/mm/trans_pgd.c
+++ b/arch/arm64/mm/trans_pgd.c
@@ -64,7 +64,7 @@ static int copy_pmd(struct trans_pgd_info *info, pud_t *dst_pudp,
unsigned long next;
unsigned long addr = start;
- if (pud_none(READ_ONCE(*dst_pudp))) {
+ if (pud_none(pudp_get(dst_pudp))) {
dst_pmdp = trans_alloc(info);
if (!dst_pmdp)
return -ENOMEM;
@@ -109,7 +109,7 @@ static int copy_pud(struct trans_pgd_info *info, p4d_t *dst_p4dp,
src_pudp = pud_offset(src_p4dp, start);
do {
- pud_t pud = READ_ONCE(*src_pudp);
+ pud_t pud = pudp_get(src_pudp);
next = pud_addr_end(addr, end);
if (pud_none(pud))
--
2.43.0
next prev parent reply other threads:[~2026-09-22 6:16 UTC|newest]
Thread overview: 15+ messages / expand[flat|nested] mbox.gz Atom feed top
2026-09-22 6:16 [PATCH V2 0/4] arm64/mm: Convert pgtable READ_ONCE() as pxdp_get() Anshuman Khandual
2026-09-22 6:16 ` [PATCH V2 1/4] arm64/mm: Use pmdp_get() for PMD accesses Anshuman Khandual
2026-09-23 8:32 ` Ryan Roberts
2026-09-23 11:01 ` Anshuman Khandual
2026-09-23 11:31 ` Ryan Roberts
2026-09-23 12:22 ` Anshuman Khandual
2026-09-23 12:50 ` Ryan Roberts
2026-09-24 2:39 ` Anshuman Khandual
2026-09-22 6:16 ` Anshuman Khandual [this message]
2026-09-22 6:16 ` [PATCH V2 3/4] arm64/mm: Use p4dp_get() for P4D accesses Anshuman Khandual
2026-09-23 8:30 ` Ryan Roberts
2026-09-24 4:23 ` Anshuman Khandual
2026-09-22 6:16 ` [PATCH V2 4/4] arm64/mm: Use pgdp_get() for PGD accesses Anshuman Khandual
2026-09-23 8:31 ` Ryan Roberts
2026-09-24 4:22 ` Anshuman Khandual
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