From: "David Hildenbrand (Arm)" <david@kernel.org>
To: Anshuman Khandual <anshuman.khandual@arm.com>,
linux-arm-kernel@lists.infradead.org
Cc: Mike Rapoport <rppt@kernel.org>,
Andrew Morton <akpm@linux-foundation.org>,
Lorenzo Stoakes <ljs@kernel.org>,
Catalin Marinas <catalin.marinas@arm.com>,
Will Deacon <will@kernel.org>,
linux-kernel@vger.kernel.org, linux-mm@kvack.org
Subject: Re: [PATCH V2 1/2] arm64/mm: Move __check_safe_pte_update()
Date: Wed, 9 Sep 2026 17:12:24 +0200 [thread overview]
Message-ID: <04358f9d-3b64-47c0-94dc-f1ef19c22f78@kernel.org> (raw)
In-Reply-To: <20260909040005.4148136-2-anshuman.khandual@arm.com>
On 9/9/26 06:00, 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@arm.com>
> Cc: Will Deacon <will@kernel.org>
> Cc: linux-arm-kernel@lists.infradead.org
> Cc: linux-kernel@vger.kernel.org
> Signed-off-by: Anshuman Khandual <anshuman.khandual@arm.com>
> ---
> Changes in V2:
>
> - Moved __check_safe_pte_update() inside #ifdef CONFIG_DEBUG_VM
> - Added empty stub for __check_safe_pte_update() when !CONFIG_DEBUG_VM
> - Dropped IS_ENABLED(CONFIG_DEBUG_VM) from __check_safe_pte_update()
>
> 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..281a512f1fc6 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
[...]
> +#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
#endif /* CONFIG_DEBUG_VM */
Might be helpful here.
Consider the same in the case above
Reviewed-by: David Hildenbrand (Arm) <david@kernel.org>
--
Cheers,
David
next prev parent reply other threads:[~2026-09-09 15:12 UTC|newest]
Thread overview: 6+ messages / expand[flat|nested] mbox.gz Atom feed top
2026-09-09 4:00 [PATCH V2 0/2] arm64/mm: Standardize printing for pgtable entries Anshuman Khandual
2026-09-09 4:00 ` [PATCH V2 1/2] arm64/mm: Move __check_safe_pte_update() Anshuman Khandual
2026-09-09 15:12 ` David Hildenbrand (Arm) [this message]
2026-09-10 4:05 ` Anshuman Khandual
2026-09-09 4:00 ` [PATCH V2 2/2] arm64/mm: Standardize printing for pgtable entries Anshuman Khandual
2026-09-09 15:14 ` David Hildenbrand (Arm)
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