[PATCH V3 1/2] arm64/mm: Move __check_safe_pte_update()
Anshuman Khandual
anshuman.khandual at arm.com
Mon Sep 28 06:50:25 PDT 2026
On Wed, Sep 16, 2026 at 10:19:32AM +0530, Anshuman Khandual wrote:
> The page table entry print helpers and related macros which are defined in
> <linux/pgtable.h> will not be accessible in platform <asm/pgtable.h> which
> is basically caused by cycling dependency.
>
> Move __check_safe_pte_update() inside arch/arm64/mm/mmu.c as a preparation
> for subsequent usage of the afore mentioned generic MM helpers. While here
> drop IS_ENABLED(CONFIG_DEBUG_VM), although wrap __check_safe_pte_update()
> inside #ifdef CONFIG_DEBUG_VM that preserves the current code optimization
> which is achieved via the static inline functions.
>
> This does not cause any functional change.
>
> Cc: Catalin Marinas <catalin.marinas at arm.com>
> Cc: Will Deacon <will at kernel.org>
> Cc: linux-arm-kernel at lists.infradead.org
> Cc: linux-kernel at vger.kernel.org
> Reviewed-by: David Hildenbrand (Arm) <david at kernel.org>
> Signed-off-by: Anshuman Khandual <anshuman.khandual at arm.com>
> ---
> arch/arm64/include/asm/pgtable.h | 49 ++++----------------------------
> arch/arm64/mm/mmu.c | 44 ++++++++++++++++++++++++++++
> 2 files changed, 49 insertions(+), 44 deletions(-)
>
> diff --git a/arch/arm64/include/asm/pgtable.h b/arch/arm64/include/asm/pgtable.h
> index e89ec5f4787b..763c5a411d64 100644
> --- a/arch/arm64/include/asm/pgtable.h
> +++ b/arch/arm64/include/asm/pgtable.h
> @@ -387,52 +387,13 @@ static inline pte_t __ptep_get(pte_t *ptep)
> extern void __sync_icache_dcache(pte_t pteval);
> bool pgattr_change_is_safe(pteval_t old, pteval_t new);
>
> -/*
> - * PTE bits configuration in the presence of hardware Dirty Bit Management
> - * (PTE_WRITE == PTE_DBM):
> - *
> - * Dirty Writable | PTE_RDONLY PTE_WRITE PTE_DIRTY (sw)
> - * 0 0 | 1 0 0
> - * 0 1 | 1 1 0
> - * 1 0 | 1 0 1
> - * 1 1 | 0 1 x
> - *
> - * When hardware DBM is not present, the software PTE_DIRTY bit is updated via
> - * the page fault mechanism. Checking the dirty status of a pte becomes:
> - *
> - * PTE_DIRTY || (PTE_WRITE && !PTE_RDONLY)
> - */
> -
> -static inline void __check_safe_pte_update(struct mm_struct *mm, pte_t *ptep,
> - pte_t pte)
> +#ifdef CONFIG_DEBUG_VM
> +void __check_safe_pte_update(struct mm_struct *mm, pte_t *ptep, pte_t pte);
> +#else
> +static inline void __check_safe_pte_update(struct mm_struct *mm, pte_t *ptep, pte_t pte)
> {
> - pte_t old_pte;
> -
> - if (!IS_ENABLED(CONFIG_DEBUG_VM))
> - return;
> -
> - old_pte = __ptep_get(ptep);
> -
> - if (!pte_valid(old_pte) || !pte_valid(pte))
> - return;
> - if (mm != current->active_mm && atomic_read(&mm->mm_users) <= 1)
> - return;
> -
> - /*
> - * Check for potential race with hardware updates of the pte
> - * (__ptep_set_access_flags safely changes valid ptes without going
> - * through an invalid entry).
> - */
> - VM_WARN_ONCE(!pte_young(pte),
> - "%s: racy access flag clearing: 0x%016llx -> 0x%016llx",
> - __func__, pte_val(old_pte), pte_val(pte));
> - VM_WARN_ONCE(pte_write(old_pte) && !pte_dirty(pte),
> - "%s: racy dirty state clearing: 0x%016llx -> 0x%016llx",
> - __func__, pte_val(old_pte), pte_val(pte));
> - VM_WARN_ONCE(!pgattr_change_is_safe(pte_val(old_pte), pte_val(pte)),
> - "%s: unsafe attribute change: 0x%016llx -> 0x%016llx",
> - __func__, pte_val(old_pte), pte_val(pte));
> }
> +#endif /* CONFIG_DEBUG_VM */
>
> static inline void __sync_cache_and_tags(pte_t pte, unsigned int nr_pages)
> {
> diff --git a/arch/arm64/mm/mmu.c b/arch/arm64/mm/mmu.c
> index 79d90226fd5d..cb49469707a8 100644
> --- a/arch/arm64/mm/mmu.c
> +++ b/arch/arm64/mm/mmu.c
> @@ -2392,4 +2392,48 @@ int arch_set_user_pkey_access(int pkey, unsigned long init_val)
>
> return 0;
> }
> +
> +/*
> + * PTE bits configuration in the presence of hardware Dirty Bit Management
> + * (PTE_WRITE == PTE_DBM):
> + *
> + * Dirty Writable | PTE_RDONLY PTE_WRITE PTE_DIRTY (sw)
> + * 0 0 | 1 0 0
> + * 0 1 | 1 1 0
> + * 1 0 | 1 0 1
> + * 1 1 | 0 1 x
> + *
> + * When hardware DBM is not present, the software PTE_DIRTY bit is updated via
> + * the page fault mechanism. Checking the dirty status of a pte becomes:
> + *
> + * PTE_DIRTY || (PTE_WRITE && !PTE_RDONLY)
> + */
> +#ifdef CONFIG_DEBUG_VM
> +void __check_safe_pte_update(struct mm_struct *mm, pte_t *ptep, pte_t pte)
> +{
> + pte_t old_pte;
> +
> + old_pte = __ptep_get(ptep);
> +
> + if (!pte_valid(old_pte) || !pte_valid(pte))
> + return;
> + if (mm != current->active_mm && atomic_read(&mm->mm_users) <= 1)
> + return;
> +
> + /*
> + * Check for potential race with hardware updates of the pte
> + * (__ptep_set_access_flags safely changes valid ptes without going
> + * through an invalid entry).
> + */
> + VM_WARN_ONCE(!pte_young(pte),
> + "%s: racy access flag clearing: 0x%016llx -> 0x%016llx",
> + __func__, pte_val(old_pte), pte_val(pte));
> + VM_WARN_ONCE(pte_write(old_pte) && !pte_dirty(pte),
> + "%s: racy dirty state clearing: 0x%016llx -> 0x%016llx",
> + __func__, pte_val(old_pte), pte_val(pte));
> + VM_WARN_ONCE(!pgattr_change_is_safe(pte_val(old_pte), pte_val(pte)),
> + "%s: unsafe attribute change: 0x%016llx -> 0x%016llx",
> + __func__, pte_val(old_pte), pte_val(pte));
> +}
> +#endif /* CONFIG_DEBUG_VM */
> #endif
> --
> 2.43.0
>
Hello Andrew,
Could you please squash in the following changes from David which fixes
the build issue reported earlier. Problem is the #ifdef CONFIG_DEBUG_VM
block was inserted inside the existing #ifdef CONFIG_ARCH_HAS_PKEYS not
after it as would have been expected. OR do we need a respin here along
with the change ?
- Anshuman
>From 448f146f16394713b28295236588ccab3a173827 Mon Sep 17 00:00:00 2001
From: "David Hildenbrand (Arm)" <david at kernel.org>
Date: Mon, 28 Sep 2026 09:42:06 +0200
Subject: [PATCH] fixup: arm64/mm: move __check_safe_pte_update()
Signed-off-by: David Hildenbrand (Arm) <david at kernel.org>
---
arch/arm64/mm/mmu.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/arch/arm64/mm/mmu.c b/arch/arm64/mm/mmu.c
index e589fb00d1e3..7343ac9294f8 100644
--- a/arch/arm64/mm/mmu.c
+++ b/arch/arm64/mm/mmu.c
@@ -2392,6 +2392,7 @@ int arch_set_user_pkey_access(int pkey, unsigned long init_val)
return 0;
}
+#endif
/*
* PTE bits configuration in the presence of hardware Dirty Bit Management
@@ -2440,4 +2441,3 @@ void __check_safe_pte_update(struct mm_struct *mm, pte_t *ptep, pte_t pte)
__func__, pte_str_old, pte_str);
}
#endif /* CONFIG_DEBUG_VM */
-#endif
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