[RFC V1 10/16] arm64/mm: Route all pgtable writes via ptdesc_set()

Anshuman Khandual
2026-02-24T05:13:19Z

Currently ptdesc_set() is defined as WRITE_ONCE() but this will change for
D128 pgtable builds, for which WRITE_ONCE() is not sufficient for single
copy atomicity.

In future this infrastructure can be used for D128 to maintain single copy
atomicity semantics with inline asm blocks.

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
Signed-off-by: Anshuman Khandual <anshuman.khandual@arm.com>
---
arch/arm64/include/asm/pgtable.h | 11 ++++++-----
arch/arm64/mm/mmu.c | 4 ++--
mm/debug_vm_pgtable.c | 4 ++--
3 files changed, 10 insertions(+), 9 deletions(-)

diff --git a/arch/arm64/include/asm/pgtable.h b/arch/arm64/include/asm/pgtable.h
index 804ef49aea88..42124d2f323d 100644
--- a/arch/arm64/include/asm/pgtable.h
+++ b/arch/arm64/include/asm/pgtable.h
@@ -85,6 +85,7 @@ static inline void arch_leave_lazy_mmu_mode(void)
}

#define ptdesc_get(x) READ_ONCE(x)
+#define ptdesc_set(x, val) WRITE_ONCE(x, val)

#define pmdp_get pmdp_get
static inline pmd_t pmdp_get(pmd_t *pmdp)
@@ -389,7 +390,7 @@ static inline pte_t pte_clear_uffd_wp(pte_t pte)

static inline void __set_pte_nosync(pte_t *ptep, pte_t pte)
{
- WRITE_ONCE(*ptep, pte);
+ ptdesc_set(*ptep, pte);
}

static inline void __set_pte_complete(pte_t pte)
@@ -856,7 +857,7 @@ static inline void set_pmd(pmd_t *pmdp, pmd_t pmd)
}
#endif /* __PAGETABLE_PMD_FOLDED */

- WRITE_ONCE(*pmdp, pmd);
+ ptdesc_set(*pmdp, pmd);

if (pmd_valid(pmd))
queue_pte_barriers();
@@ -917,7 +918,7 @@ static inline void set_pud(pud_t *pudp, pud_t pud)
return;
}

- WRITE_ONCE(*pudp, pud);
+ ptdesc_set(*pudp, pud);

if (pud_valid(pud))
queue_pte_barriers();
@@ -999,7 +1000,7 @@ static inline void set_p4d(p4d_t *p4dp, p4d_t p4d)
return;
}

- WRITE_ONCE(*p4dp, p4d);
+ ptdesc_set(*p4dp, p4d);
queue_pte_barriers();
}

@@ -1120,7 +1121,7 @@ static inline void set_pgd(pgd_t *pgdp, pgd_t pgd)
return;
}

- WRITE_ONCE(*pgdp, pgd);
+ ptdesc_set(*pgdp, pgd);
queue_pte_barriers();
}

diff --git a/arch/arm64/mm/mmu.c b/arch/arm64/mm/mmu.c
index bcf32d1a92de..ffd307c546f5 100644
--- a/arch/arm64/mm/mmu.c
+++ b/arch/arm64/mm/mmu.c
@@ -83,7 +83,7 @@ void noinstr set_swapper_pgd(pgd_t *pgdp, pgd_t pgd)
* writable in the kernel mapping.
*/
if (rodata_is_rw) {
- WRITE_ONCE(*pgdp, pgd);
+ ptdesc_set(*pgdp, pgd);
dsb(ishst);
isb();
return;
@@ -91,7 +91,7 @@ void noinstr set_swapper_pgd(pgd_t *pgdp, pgd_t pgd)

spin_lock(&swapper_pgdir_lock);
fixmap_pgdp = pgd_set_fixmap(__pa_symbol(pgdp));
- WRITE_ONCE(*fixmap_pgdp, pgd);
+ ptdesc_set(*fixmap_pgdp, pgd);
/*
* We need dsb(ishst) here to ensure the page-table-walker sees
* our new entry before set_p?d() returns. The fixmap's
diff --git a/mm/debug_vm_pgtable.c b/mm/debug_vm_pgtable.c
index 83cf07269f13..faf6a19a89a1 100644
--- a/mm/debug_vm_pgtable.c
+++ b/mm/debug_vm_pgtable.c
@@ -445,7 +445,7 @@ static void __init pmd_huge_tests(struct pgtable_debug_args *args)
* X86 defined pmd_set_huge() verifies that the given
* PMD is not a populated non-leaf entry.
*/
- WRITE_ONCE(*args->pmdp, __pmd(0));
+ ptdesc_set(*args->pmdp, __pmd(0));
WARN_ON(!pmd_set_huge(args->pmdp, __pfn_to_phys(args->fixed_pmd_pfn), args->page_prot));
WARN_ON(!pmd_clear_huge(args->pmdp));
pmd = pmdp_get(args->pmdp);
@@ -465,7 +465,7 @@ static void __init pud_huge_tests(struct pgtable_debug_args *args)
* X86 defined pud_set_huge() verifies that the given
* PUD is not a populated non-leaf entry.
*/
- WRITE_ONCE(*args->pudp, __pud(0));
+ ptdesc_set(*args->pudp, __pud(0));
WARN_ON(!pud_set_huge(args->pudp, __pfn_to_phys(args->fixed_pud_pfn), args->page_prot));
WARN_ON(!pud_clear_huge(args->pudp));
pud = pudp_get(args->pudp);
--
2.43.0