Re: [RFC V1 09/16] arm64/mm: Route all pgtable reads via ptdesc_get()

[Mike Rapoport]

Hi Anshuman,

On Tue, Feb 24, 2026 at 10:41:46AM +0530, Anshuman Khandual wrote:
> Define arm64 platform specific implementations for new pXdp_get() helpers.
> These resolve into READ_ONCE(), thus ensuring required single copy atomic
> semantics for the page table entry reads.
> 
> In future this infrastructure can be used for D128 to maintain single copy
> atomicity semantics with inline asm blocks.
> 
> Cc: Catalin Marinas <catalin.marinas@xxxxxxx>
> Cc: Will Deacon <will@xxxxxxxxxx>
> Cc: Ryan Roberts <ryan.roberts@xxxxxxx>
> Cc: Mark Rutland <mark.rutland@xxxxxxx>
> Cc: linux-arm-kernel@xxxxxxxxxxxxxxxxxxx
> Cc: linux-kernel@xxxxxxxxxxxxxxx
> Signed-off-by: Anshuman Khandual <anshuman.khandual@xxxxxxx>
> ---
>  arch/arm64/include/asm/pgtable.h | 28 +++++++++++++++++++++++++++-
>  1 file changed, 27 insertions(+), 1 deletion(-)
> 
> diff --git a/arch/arm64/include/asm/pgtable.h b/arch/arm64/include/asm/pgtable.h
> index 257af1c3015d..804ef49aea88 100644
> --- a/arch/arm64/include/asm/pgtable.h
> +++ b/arch/arm64/include/asm/pgtable.h
> @@ -84,6 +84,32 @@ static inline void arch_leave_lazy_mmu_mode(void)
>  	arch_flush_lazy_mmu_mode();
>  }
>  
> +#define ptdesc_get(x)		READ_ONCE(x)

This will be confusing with 'struct ptdesc' APIs, maybe ptent_get()?

> +#define pmdp_get pmdp_get
> +static inline pmd_t pmdp_get(pmd_t *pmdp)
> +{
> +	return ptdesc_get(*pmdp);
> +}
> +
> +#define pudp_get pudp_get
> +static inline pud_t pudp_get(pud_t *pudp)
> +{
> +	return ptdesc_get(*pudp);
> +}
> +
> +#define p4dp_get p4dp_get
> +static inline p4d_t p4dp_get(p4d_t *p4dp)
> +{
> +	return ptdesc_get(*p4dp);
> +}
> +
> +#define pgdp_get pgdp_get
> +static inline pgd_t pgdp_get(pgd_t *pgdp)
> +{
> +	return ptdesc_get(*pgdp);
> +}
> +
>  #ifdef CONFIG_TRANSPARENT_HUGEPAGE
>  #define __HAVE_ARCH_FLUSH_PMD_TLB_RANGE
>  
> @@ -384,7 +410,7 @@ static inline void __set_pte(pte_t *ptep, pte_t pte)
>  
>  static inline pte_t __ptep_get(pte_t *ptep)
>  {
> -	return READ_ONCE(*ptep);
> +	return ptdesc_get(*ptep);
>  }
>  
>  extern void __sync_icache_dcache(pte_t pteval);
> -- 
> 2.43.0
> 

-- 
Sincerely yours,
Mike.