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 4/4] arm64/mm: Use pgdp_get() for PGD accesses
Date: Thu, 5 Nov 2026 10:04:03 +0530 [thread overview]
Message-ID: <20261105043403.3326445-5-anshuman.khandual@arm.com> (raw)
In-Reply-To: <20261105043403.3326445-1-anshuman.khandual@arm.com>
Replace READ_ONCE() with pgdp_get() for PGD 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 PGD accesses on the existing page-table helpers.
These can be overridden on arm64 to provide 128-bit single-copy
atomicity when required.
Both READ_ONCE() instances in p4d_offset_[phys]() could not be converted
into pgpd_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 pgdp_get() platform override
- Moved both p4d_offset[_phys]() inside arch/arm64/mm/mmu.c
arch/arm64/include/asm/pgtable.h | 12 ++----------
arch/arm64/mm/fault.c | 2 +-
arch/arm64/mm/hugetlbpage.c | 2 +-
arch/arm64/mm/kasan_init.c | 6 +++---
arch/arm64/mm/mmu.c | 20 +++++++++++++++++---
arch/arm64/mm/pageattr.c | 2 +-
arch/arm64/mm/trans_pgd.c | 4 ++--
7 files changed, 27 insertions(+), 21 deletions(-)
diff --git a/arch/arm64/include/asm/pgtable.h b/arch/arm64/include/asm/pgtable.h
index 8dffa7f787ac..6a38de07e599 100644
--- a/arch/arm64/include/asm/pgtable.h
+++ b/arch/arm64/include/asm/pgtable.h
@@ -1072,12 +1072,7 @@ static inline p4d_t *pgd_to_folded_p4d(pgd_t *pgdp, unsigned long addr)
return (p4d_t *)PTR_ALIGN_DOWN(pgdp, PAGE_SIZE) + p4d_index(addr);
}
-static inline phys_addr_t p4d_offset_phys(pgd_t *pgdp, unsigned long addr)
-{
- VM_WARN_ON_ONCE(!pgtable_l5_enabled());
-
- return pgd_page_paddr(READ_ONCE(*pgdp)) + p4d_index(addr) * sizeof(p4d_t);
-}
+phys_addr_t p4d_offset_phys(pgd_t *pgdp, unsigned long addr);
static inline
p4d_t *p4d_offset_lockless(pgd_t *pgdp, pgd_t pgd, unsigned long addr)
@@ -1088,10 +1083,7 @@ p4d_t *p4d_offset_lockless(pgd_t *pgdp, pgd_t pgd, unsigned long addr)
}
#define p4d_offset_lockless p4d_offset_lockless
-static inline p4d_t *p4d_offset(pgd_t *pgdp, unsigned long addr)
-{
- return p4d_offset_lockless(pgdp, READ_ONCE(*pgdp), addr);
-}
+p4d_t *p4d_offset(pgd_t *pgdp, unsigned long addr);
static inline p4d_t *p4d_set_fixmap(unsigned long addr)
{
diff --git a/arch/arm64/mm/fault.c b/arch/arm64/mm/fault.c
index 934b534c5b89..0b489fbeeb07 100644
--- a/arch/arm64/mm/fault.c
+++ b/arch/arm64/mm/fault.c
@@ -160,7 +160,7 @@ static void show_pte(unsigned long addr)
guard(irqsave)();
pgdp = pgd_offset(mm, addr);
- pgd = READ_ONCE(*pgdp);
+ pgd = pgdp_get(pgdp);
ptval_to_str(pxd_str, pgd_val(pgd));
pr_alert("[%016lx] pgd=%s", addr, pxd_str);
diff --git a/arch/arm64/mm/hugetlbpage.c b/arch/arm64/mm/hugetlbpage.c
index 5771bf49e1fe..e05e5b41ae50 100644
--- a/arch/arm64/mm/hugetlbpage.c
+++ b/arch/arm64/mm/hugetlbpage.c
@@ -284,7 +284,7 @@ pte_t *huge_pte_offset(struct mm_struct *mm,
pmd_t *pmdp, pmd;
pgdp = pgd_offset(mm, addr);
- if (!pgd_present(READ_ONCE(*pgdp)))
+ if (!pgd_present(pgdp_get(pgdp)))
return NULL;
p4dp = p4d_offset(pgdp, addr);
diff --git a/arch/arm64/mm/kasan_init.c b/arch/arm64/mm/kasan_init.c
index 4dd8c1186471..f61f5bc09467 100644
--- a/arch/arm64/mm/kasan_init.c
+++ b/arch/arm64/mm/kasan_init.c
@@ -102,7 +102,7 @@ static pud_t *__init kasan_pud_offset(p4d_t *p4dp, unsigned long addr, int node,
static p4d_t *__init kasan_p4d_offset(pgd_t *pgdp, unsigned long addr, int node,
bool early)
{
- if (pgd_none(READ_ONCE(*pgdp))) {
+ if (pgd_none(pgdp_get(pgdp))) {
phys_addr_t p4d_phys = early ?
__pa_symbol(kasan_early_shadow_p4d)
: kasan_alloc_zeroed_page(node);
@@ -256,7 +256,7 @@ static int __init root_level_idx(u64 addr)
static void __init clone_next_level(u64 addr, pgd_t *tmp_pg_dir, pud_t *pud)
{
int idx = root_level_idx(addr);
- pgd_t pgd = READ_ONCE(swapper_pg_dir[idx]);
+ pgd_t pgd = pgdp_get(swapper_pg_dir + idx);
pud_t *pudp = (pud_t *)__phys_to_kimg(__pgd_to_phys(pgd));
memcpy(pud, pudp, PAGE_SIZE);
@@ -280,7 +280,7 @@ static int __init next_level_idx(u64 addr)
*/
static void __init clear_next_level(int pgd_idx, int start, int end)
{
- pgd_t pgd = READ_ONCE(swapper_pg_dir[pgd_idx]);
+ pgd_t pgd = pgdp_get(swapper_pg_dir + pgd_idx);
pud_t *pudp = (pud_t *)__phys_to_kimg(__pgd_to_phys(pgd));
memset(&pudp[start], 0, (end - start) * sizeof(pud_t));
diff --git a/arch/arm64/mm/mmu.c b/arch/arm64/mm/mmu.c
index 711d734a63f7..1f56db9a946c 100644
--- a/arch/arm64/mm/mmu.c
+++ b/arch/arm64/mm/mmu.c
@@ -434,7 +434,7 @@ static int alloc_init_p4d(pgd_t *pgdp, unsigned long addr, unsigned long end,
{
int ret;
unsigned long next;
- pgd_t pgd = READ_ONCE(*pgdp);
+ pgd_t pgd = pgdp_get(pgdp);
p4d_t *p4dp;
if (pgd_none(pgd)) {
@@ -1649,7 +1649,7 @@ static void unmap_hotplug_range(unsigned long addr, unsigned long end,
do {
next = pgd_addr_end(addr, end);
pgdp = pgd_offset_k(addr);
- pgd = READ_ONCE(*pgdp);
+ pgd = pgdp_get(pgdp);
if (pgd_none(pgd))
continue;
@@ -1827,7 +1827,7 @@ static void free_empty_tables(unsigned long addr, unsigned long end,
do {
next = pgd_addr_end(addr, end);
pgdp = pgd_offset_k(addr);
- pgd = READ_ONCE(*pgdp);
+ pgd = pgdp_get(pgdp);
if (pgd_none(pgd))
continue;
@@ -2464,3 +2464,17 @@ pud_t *pud_offset(p4d_t *p4dp, unsigned long addr)
return pud_offset_lockless(p4dp, p4dp_get(p4dp), addr);
}
#endif /* CONFIG_PGTABLE_LEVELS > 3 */
+
+#if CONFIG_PGTABLE_LEVELS > 4
+phys_addr_t p4d_offset_phys(pgd_t *pgdp, unsigned long addr)
+{
+ VM_WARN_ON_ONCE(!pgtable_l5_enabled());
+
+ return pgd_page_paddr(pgdp_get(pgdp)) + p4d_index(addr) * sizeof(p4d_t);
+}
+
+p4d_t *p4d_offset(pgd_t *pgdp, unsigned long addr)
+{
+ return p4d_offset_lockless(pgdp, pgdp_get(pgdp), addr);
+}
+#endif /* CONFIG_PGTABLE_LEVELS > 4 */
diff --git a/arch/arm64/mm/pageattr.c b/arch/arm64/mm/pageattr.c
index 172bc516164c..b3b7c508564f 100644
--- a/arch/arm64/mm/pageattr.c
+++ b/arch/arm64/mm/pageattr.c
@@ -347,7 +347,7 @@ bool kernel_page_present(struct page *page)
unsigned long addr = (unsigned long)page_address(page);
pgdp = pgd_offset_k(addr);
- if (pgd_none(READ_ONCE(*pgdp)))
+ if (pgd_none(pgdp_get(pgdp)))
return false;
p4dp = p4d_offset(pgdp, addr);
diff --git a/arch/arm64/mm/trans_pgd.c b/arch/arm64/mm/trans_pgd.c
index 7afe2beca4ba..06470d690f9f 100644
--- a/arch/arm64/mm/trans_pgd.c
+++ b/arch/arm64/mm/trans_pgd.c
@@ -134,7 +134,7 @@ static int copy_p4d(struct trans_pgd_info *info, pgd_t *dst_pgdp,
unsigned long next;
unsigned long addr = start;
- if (pgd_none(READ_ONCE(*dst_pgdp))) {
+ if (pgd_none(pgdp_get(dst_pgdp))) {
dst_p4dp = trans_alloc(info);
if (!dst_p4dp)
return -ENOMEM;
@@ -164,7 +164,7 @@ static int copy_page_tables(struct trans_pgd_info *info, pgd_t *dst_pgdp,
dst_pgdp = pgd_offset_pgd(dst_pgdp, start);
do {
next = pgd_addr_end(addr, end);
- if (pgd_none(READ_ONCE(*src_pgdp)))
+ if (pgd_none(pgdp_get(src_pgdp)))
continue;
if (copy_p4d(info, dst_pgdp, src_pgdp, addr, next))
return -ENOMEM;
--
2.43.0
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 ` [PATCH V4 1/4] arm64/mm: Use pmdp_get() for PMD accesses Anshuman Khandual
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 ` Anshuman Khandual [this message]
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