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 V3 3/4] arm64/mm: Use p4dp_get() for P4D accesses
Date: Thu, 24 Sep 2026 11:52:13 +0530 [thread overview]
Message-ID: <20260924062214.1635078-4-anshuman.khandual@arm.com> (raw)
In-Reply-To: <20260924062214.1635078-1-anshuman.khandual@arm.com>
Replace READ_ONCE() with p4dp_get() for P4D 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 P4D accesses on the existing page-table helpers.
These can be overridden on arm64 to provide 128-bit single-copy
atomicity when required.
For now override p4dp_get() which is same as the generic memory default
to avoid build dependency problem for callers in header <asm/pgtable.h>.
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>
---
Changes in V3
- Added platform override for p4dp_get()
- Replaced READ_ONCE() in pud_offset_phys() and pud_offset()
arch/arm64/include/asm/pgtable.h | 10 ++++++++--
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 | 12 ++++++------
arch/arm64/mm/pageattr.c | 2 +-
arch/arm64/mm/trans_pgd.c | 4 ++--
8 files changed, 22 insertions(+), 16 deletions(-)
diff --git a/arch/arm64/include/asm/pgtable.h b/arch/arm64/include/asm/pgtable.h
index b46930f844a2..f235f68a7518 100644
--- a/arch/arm64/include/asm/pgtable.h
+++ b/arch/arm64/include/asm/pgtable.h
@@ -96,6 +96,12 @@ static inline pud_t pudp_get(pud_t *pudp)
return READ_ONCE(*pudp);
}
+#define p4dp_get p4dp_get
+static inline p4d_t p4dp_get(p4d_t *p4dp)
+{
+ return READ_ONCE(*p4dp);
+}
+
#ifdef CONFIG_TRANSPARENT_HUGEPAGE
#define __HAVE_ARCH_FLUSH_PMD_TLB_RANGE
@@ -976,7 +982,7 @@ static inline phys_addr_t pud_offset_phys(p4d_t *p4dp, unsigned long addr)
{
VM_WARN_ON_ONCE(!pgtable_l4_enabled());
- return p4d_page_paddr(READ_ONCE(*p4dp)) + pud_index(addr) * sizeof(pud_t);
+ return p4d_page_paddr(p4dp_get(p4dp)) + pud_index(addr) * sizeof(pud_t);
}
static inline
@@ -990,7 +996,7 @@ pud_t *pud_offset_lockless(p4d_t *p4dp, p4d_t p4d, unsigned long addr)
static inline pud_t *pud_offset(p4d_t *p4dp, unsigned long addr)
{
- return pud_offset_lockless(p4dp, READ_ONCE(*p4dp), addr);
+ return pud_offset_lockless(p4dp, p4dp_get(p4dp), addr);
}
#define pud_offset pud_offset
diff --git a/arch/arm64/mm/fault.c b/arch/arm64/mm/fault.c
index 435e2e14c070..a6afd8929a10 100644
--- a/arch/arm64/mm/fault.c
+++ b/arch/arm64/mm/fault.c
@@ -174,7 +174,7 @@ static void show_pte(unsigned long addr)
break;
p4dp = p4d_offset_lockless(pgdp, pgd, addr);
- p4d = READ_ONCE(*p4dp);
+ p4d = p4dp_get(p4dp);
ptval_to_str(pxd_str, p4d_val(p4d));
pr_cont(", p4d=%s", pxd_str);
if (p4d_none(p4d) || p4d_bad(p4d))
diff --git a/arch/arm64/mm/fixmap.c b/arch/arm64/mm/fixmap.c
index d9a870836faf..2a0fe0b0f771 100644
--- a/arch/arm64/mm/fixmap.c
+++ b/arch/arm64/mm/fixmap.c
@@ -74,7 +74,7 @@ static void __init early_fixmap_init_pmd(pud_t *pudp, unsigned long addr,
static void __init early_fixmap_init_pud(p4d_t *p4dp, unsigned long addr,
unsigned long end)
{
- p4d_t p4d = READ_ONCE(*p4dp);
+ p4d_t p4d = p4dp_get(p4dp);
pud_t *pudp;
if (CONFIG_PGTABLE_LEVELS > 3 && !p4d_none(p4d) &&
diff --git a/arch/arm64/mm/hugetlbpage.c b/arch/arm64/mm/hugetlbpage.c
index c9ad5e75b073..5771bf49e1fe 100644
--- a/arch/arm64/mm/hugetlbpage.c
+++ b/arch/arm64/mm/hugetlbpage.c
@@ -288,7 +288,7 @@ pte_t *huge_pte_offset(struct mm_struct *mm,
return NULL;
p4dp = p4d_offset(pgdp, addr);
- if (!p4d_present(READ_ONCE(*p4dp)))
+ if (!p4d_present(p4dp_get(p4dp)))
return NULL;
pudp = pud_offset(p4dp, addr);
diff --git a/arch/arm64/mm/kasan_init.c b/arch/arm64/mm/kasan_init.c
index aad29bcc7622..4dd8c1186471 100644
--- a/arch/arm64/mm/kasan_init.c
+++ b/arch/arm64/mm/kasan_init.c
@@ -89,7 +89,7 @@ static pmd_t *__init kasan_pmd_offset(pud_t *pudp, unsigned long addr, int node,
static pud_t *__init kasan_pud_offset(p4d_t *p4dp, unsigned long addr, int node,
bool early)
{
- if (p4d_none(READ_ONCE(*p4dp))) {
+ if (p4d_none(p4dp_get(p4dp))) {
phys_addr_t pud_phys = early ?
__pa_symbol(kasan_early_shadow_pud)
: kasan_alloc_zeroed_page(node);
@@ -162,7 +162,7 @@ static void __init kasan_p4d_populate(pgd_t *pgdp, unsigned long addr,
do {
next = p4d_addr_end(addr, end);
kasan_pud_populate(p4dp, addr, next, node, early);
- } while (p4dp++, addr = next, addr != end && p4d_none(READ_ONCE(*p4dp)));
+ } while (p4dp++, addr = next, addr != end && p4d_none(p4dp_get(p4dp)));
}
static void __init kasan_pgd_populate(unsigned long addr, unsigned long end,
diff --git a/arch/arm64/mm/mmu.c b/arch/arm64/mm/mmu.c
index 22efaee79293..83709d987e7c 100644
--- a/arch/arm64/mm/mmu.c
+++ b/arch/arm64/mm/mmu.c
@@ -367,7 +367,7 @@ static int alloc_init_pud(p4d_t *p4dp, unsigned long addr, unsigned long end,
{
int ret = 0;
unsigned long next;
- p4d_t p4d = READ_ONCE(*p4dp);
+ p4d_t p4d = p4dp_get(p4dp);
pud_t *pudp;
if (p4d_none(p4d)) {
@@ -457,7 +457,7 @@ static int alloc_init_p4d(pgd_t *pgdp, unsigned long addr, unsigned long end,
}
do {
- p4d_t old_p4d = READ_ONCE(*p4dp);
+ p4d_t old_p4d = p4dp_get(p4dp);
next = p4d_addr_end(addr, end);
@@ -467,7 +467,7 @@ static int alloc_init_p4d(pgd_t *pgdp, unsigned long addr, unsigned long end,
goto out;
VM_WARN_ON_ONCE(p4d_val(old_p4d) != 0 &&
- p4d_val(old_p4d) != READ_ONCE(p4d_val(*p4dp)));
+ p4d_val(old_p4d) != (p4d_val(p4dp_get(p4dp))));
phys += next - addr;
} while (p4dp++, addr = next, addr != end);
@@ -1622,7 +1622,7 @@ static void unmap_hotplug_p4d_range(pgd_t *pgdp, unsigned long addr,
do {
next = p4d_addr_end(addr, end);
p4dp = p4d_offset(pgdp, addr);
- p4d = READ_ONCE(*p4dp);
+ p4d = p4dp_get(p4dp);
if (p4d_none(p4d))
continue;
@@ -1788,7 +1788,7 @@ static void free_empty_p4d_table(pgd_t *pgdp, unsigned long addr,
do {
next = p4d_addr_end(addr, end);
p4dp = p4d_offset(pgdp, addr);
- p4d = READ_ONCE(*p4dp);
+ p4d = p4dp_get(p4dp);
if (p4d_none(p4d))
continue;
@@ -1809,7 +1809,7 @@ static void free_empty_p4d_table(pgd_t *pgdp, unsigned long addr,
*/
p4dp = p4d_offset(pgdp, 0UL);
for (i = 0; i < PTRS_PER_P4D; i++) {
- if (!p4d_none(READ_ONCE(p4dp[i])))
+ if (!p4d_none(p4dp_get(p4dp + i)))
return;
}
diff --git a/arch/arm64/mm/pageattr.c b/arch/arm64/mm/pageattr.c
index 07b2fa4de57f..826856ef64a8 100644
--- a/arch/arm64/mm/pageattr.c
+++ b/arch/arm64/mm/pageattr.c
@@ -403,7 +403,7 @@ bool kernel_page_present(struct page *page)
return false;
p4dp = p4d_offset(pgdp, addr);
- if (p4d_none(READ_ONCE(*p4dp)))
+ if (p4d_none(p4dp_get(p4dp)))
return false;
pudp = pud_offset(p4dp, addr);
diff --git a/arch/arm64/mm/trans_pgd.c b/arch/arm64/mm/trans_pgd.c
index d119119455f1..7afe2beca4ba 100644
--- a/arch/arm64/mm/trans_pgd.c
+++ b/arch/arm64/mm/trans_pgd.c
@@ -99,7 +99,7 @@ static int copy_pud(struct trans_pgd_info *info, p4d_t *dst_p4dp,
unsigned long next;
unsigned long addr = start;
- if (p4d_none(READ_ONCE(*dst_p4dp))) {
+ if (p4d_none(p4dp_get(dst_p4dp))) {
dst_pudp = trans_alloc(info);
if (!dst_pudp)
return -ENOMEM;
@@ -145,7 +145,7 @@ static int copy_p4d(struct trans_pgd_info *info, pgd_t *dst_pgdp,
src_p4dp = p4d_offset(src_pgdp, start);
do {
next = p4d_addr_end(addr, end);
- if (p4d_none(READ_ONCE(*src_p4dp)))
+ if (p4d_none(p4dp_get(src_p4dp)))
continue;
if (copy_pud(info, dst_p4dp, src_p4dp, addr, next))
return -ENOMEM;
--
2.43.0
next prev parent reply other threads:[~2026-09-24 6:22 UTC|newest]
Thread overview: 12+ messages / expand[flat|nested] mbox.gz Atom feed top
2026-09-24 6:22 [PATCH V3 0/4] arm64/mm: Convert pgtable READ_ONCE() as pxdp_get() Anshuman Khandual
2026-09-24 6:22 ` [PATCH V3 1/4] arm64/mm: Use pmdp_get() for PMD accesses Anshuman Khandual
2026-09-24 12:09 ` Ryan Roberts
2026-10-05 15:31 ` Catalin Marinas
2026-10-07 2:41 ` Anshuman Khandual
2026-09-24 6:22 ` [PATCH V3 2/4] arm64/mm: Use pudp_get() for PUD accesses Anshuman Khandual
2026-09-24 12:10 ` Ryan Roberts
2026-09-24 6:22 ` Anshuman Khandual [this message]
2026-09-24 12:10 ` [PATCH V3 3/4] arm64/mm: Use p4dp_get() for P4D accesses Ryan Roberts
2026-09-24 6:22 ` [PATCH V3 4/4] arm64/mm: Use pgdp_get() for PGD accesses Anshuman Khandual
2026-09-24 12:10 ` Ryan Roberts
2026-10-05 6:41 ` [PATCH V3 0/4] arm64/mm: Convert pgtable READ_ONCE() as pxdp_get() Anshuman Khandual
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