Thread (63 messages) 63 messages, 7 authors, 2026-04-15

[RFC V1 05/16] arm64/mm: Convert READ_ONCE() as pmdp_get() while accessing PMD

From: Anshuman Khandual <hidden>
Date: 2026-02-24 05:12:51
Also in: linux-mm, lkml
Subsystem: arm64 port (aarch64 architecture), kasan, the rest · Maintainers: Catalin Marinas, Will Deacon, Andrey Ryabinin, Linus Torvalds 

Convert all READ_ONCE() based PMD accesses as pmdp_get() instead which will
support both D64 and D128 translation regime going forward.

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 <redacted>
---
 arch/arm64/include/asm/pgtable.h | 12 +++--------
 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              | 35 ++++++++++++++++++++++----------
 arch/arm64/mm/pageattr.c         |  2 +-
 arch/arm64/mm/trans_pgd.c        |  2 +-
 8 files changed, 34 insertions(+), 27 deletions(-)

diff --git a/arch/arm64/include/asm/pgtable.h b/arch/arm64/include/asm/pgtable.h
index b3e58735c49b..4b5bc2c09bf2 100644
--- a/arch/arm64/include/asm/pgtable.h
+++ b/arch/arm64/include/asm/pgtable.h
@@ -852,7 +852,8 @@ 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))
@@ -1328,14 +1329,7 @@ static inline int __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 int 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);
-}
+int 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 be9dab2c7d6a..1389ba26ec74 100644
--- a/arch/arm64/mm/fault.c
+++ b/arch/arm64/mm/fault.c
@@ -177,7 +177,7 @@ static void show_pte(unsigned long addr)
 			break;
 
 		pmdp = pmd_offset(pudp, addr);
-		pmd = READ_ONCE(*pmdp);
+		pmd = pmdp_get(pmdp);
 		pr_cont(", pmd=%016llx", pmd_val(pmd));
 		if (pmd_none(pmd) || pmd_bad(pmd))
 			break;
diff --git a/arch/arm64/mm/fixmap.c b/arch/arm64/mm/fixmap.c
index c5c5425791da..7a4bbcb39094 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 a42c05cf5640..6117aca2bac7 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 abeb81bf6ebd..709e8ad15603 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 a6a00accf4f9..dea1b595f237 100644
--- a/arch/arm64/mm/mmu.c
+++ b/arch/arm64/mm/mmu.c
@@ -201,7 +201,7 @@ 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_sect(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);
 
@@ -271,7 +271,7 @@ 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;
 
@@ -281,7 +281,7 @@ static int init_pmd(pmd_t *pmdp, unsigned long addr, unsigned long end,
 				return ret;
 
 			BUG_ON(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);
@@ -1475,7 +1475,7 @@ 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;
 
@@ -1623,7 +1623,7 @@ 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;
 
@@ -1644,7 +1644,7 @@ 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;
 	}
 
@@ -1763,7 +1763,7 @@ int __meminit vmemmap_check_pmd(pmd_t *pmdp, int node,
 {
 	vmemmap_verify((pte_t *)pmdp, node, addr, next);
 
-	return pmd_sect(READ_ONCE(*pmdp));
+	return pmd_sect(pmdp_get(pmdp));
 }
 
 int __meminit vmemmap_populate(unsigned long start, unsigned long end, int node,
@@ -1810,7 +1810,7 @@ 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;
 
@@ -1835,7 +1835,7 @@ int pud_clear_huge(pud_t *pudp)
 
 int pmd_clear_huge(pmd_t *pmdp)
 {
-	if (!pmd_sect(READ_ONCE(*pmdp)))
+	if (!pmd_sect(pmdp_get(pmdp)))
 		return 0;
 	pmd_clear(pmdp);
 	return 1;
@@ -1847,7 +1847,7 @@ static 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);
@@ -2245,4 +2245,17 @@ int arch_set_user_pkey_access(struct task_struct *tsk, int pkey, unsigned long i
 
 	return 0;
 }
+
+#if defined(CONFIG_TRANSPARENT_HUGEPAGE) || defined(CONFIG_ARCH_HAS_NONLEAF_PMD_YOUNG)
+int pmdp_test_and_clear_young(struct vm_area_struct *vma,
+			      unsigned long address, pmd_t *pmdp)
+{
+	pmd_t pmdval = pmdp_get(pmdp);
+
+	/* Operation applies to PMD table entry only if FEAT_HAFT is enabled */
+	VM_WARN_ON(pmd_table(pmdval) && !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
diff --git a/arch/arm64/mm/pageattr.c b/arch/arm64/mm/pageattr.c
index 358d1dc9a576..ed1eec4c757d 100644
--- a/arch/arm64/mm/pageattr.c
+++ b/arch/arm64/mm/pageattr.c
@@ -408,7 +408,7 @@ bool kernel_page_present(struct page *page)
 		return true;
 
 	pmdp = pmd_offset(pudp, addr);
-	pmd = READ_ONCE(*pmdp);
+	pmd = pmdp_get(pmdp);
 	if (pmd_none(pmd))
 		return false;
 	if (pmd_sect(pmd))
diff --git a/arch/arm64/mm/trans_pgd.c b/arch/arm64/mm/trans_pgd.c
index 18543b603c77..ddde0f2983b0 100644
--- a/arch/arm64/mm/trans_pgd.c
+++ b/arch/arm64/mm/trans_pgd.c
@@ -100,7 +100,7 @@ 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
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