Re: [PATCH 3/6] arm64: convert between HW PTEs and SW PTE values

[Ryan Roberts <ryan.roberts@arm.com>]

On 14/09/2026 14:51, Muhammad Usama Anjum wrote:
> __ptep_get() returns a SW PTE value, and __set_pte_nosync() accepts one.
> When HW PTEs use a distinct hw_pte_t, directly reading or writing *ptep
> as a SW PTE value no longer satisfies those interfaces.
> 
> Use __pte_from_hw after READ_ONCE() to obtain a SW PTE value and add
> __hw_pte before WRITE_ONCE() to form an HW PTE.
> 
> Define __hw_pte for both the wrapper and alias configurations so the
> same accessor code works in either case.
> 
> Signed-off-by: Muhammad Usama Anjum <usama.anjum@arm.com>
> ---
>  arch/arm64/include/asm/pgtable.h | 4 ++--
>  include/linux/pgtable_types.h    | 2 ++
>  2 files changed, 4 insertions(+), 2 deletions(-)
> 
> diff --git a/arch/arm64/include/asm/pgtable.h b/arch/arm64/include/asm/pgtable.h
> index 4768ec59de555..67c4a6179e154 100644
> --- a/arch/arm64/include/asm/pgtable.h
> +++ b/arch/arm64/include/asm/pgtable.h
> @@ -360,7 +360,7 @@ static inline pte_t pte_clear_uffd(pte_t pte)
>  
>  static inline void __set_pte_nosync(hw_pte_t *ptep, pte_t pte)
>  {
> -	WRITE_ONCE(*ptep, pte);
> +	WRITE_ONCE(*ptep, __hw_pte(pte));

Would this work as an alternative? It removes the need for the new __hw_pte()
helper. In future, converting a pte_t to a hw_pte_t won't be trivial so having a
generic helper for it doesn't feel like a good fit.

	WRITE_ONCE(hw_pte_val(*ptep), pte_val(pte));

In general, I wonder if we should avoid defining both the __hw_pte() and
__pte_from_hw() generic helpers. Conversion between sw and hw representations
will become arch-specific in future and for arm64 that conversion will need
extra information so it's can't just specialize these interfaces as they are.

>  }
>  
>  static inline void __set_pte_complete(pte_t pte)
> @@ -381,7 +381,7 @@ static inline void __set_pte(hw_pte_t *ptep, pte_t pte)
>  
>  static inline pte_t __ptep_get(hw_pte_t *ptep)
>  {
> -	return READ_ONCE(*ptep);
> +	return __pte_from_hw(READ_ONCE(*ptep));


...Corresponds with:

	return __pte(READ_ONCE(hw_pte_val(*ptep)));

Thanks,
Ryan

>  }
>  
>  extern void __sync_icache_dcache(pte_t pteval);
> diff --git a/include/linux/pgtable_types.h b/include/linux/pgtable_types.h
> index ee4eace5c3e1c..b5862a16aa497 100644
> --- a/include/linux/pgtable_types.h
> +++ b/include/linux/pgtable_types.h
> @@ -9,11 +9,13 @@
>  #ifdef CONFIG_ARCH_HAS_HW_PTE_T
>  typedef struct __hw_pte_t { pte_t __pte; } hw_pte_t;
>  #define __pte_from_hw(pte)	((pte).__pte)
> +#define __hw_pte(pte)  ((hw_pte_t) { (pte) })
>  
>  #define hw_pte_val(x)  pte_val((x).__pte)
>  #else
>  #define hw_pte_t pte_t
>  #define __pte_from_hw(pte)	(pte)
> +#define __hw_pte(pte)  (pte)
>  
>  #define hw_pte_val(x)  pte_val(x)
>  #endif
>