Subject: Re: [PATCH v2 6/8] s390/pgtable: support __HAVE_ARCH_PTE_SWP_EXCLUSIVE

From: Gerald Schaefer <[email-masked]>
Date: Wed, 30 Mar 2022 18:48:45 +0200

On Tue, 29 Mar 2022 18:43:27 +0200
David Hildenbrand <[email-masked]> wrote:

> Let's use bit 52, which is unused.
> 
> Signed-off-by: David Hildenbrand <[email-masked]>
> ---
>  arch/s390/include/asm/pgtable.h | 23 +++++++++++++++++++++--
>  1 file changed, 21 insertions(+), 2 deletions(-)
> 
> diff --git a/arch/s390/include/asm/pgtable.h b/arch/s390/include/asm/pgtable.h
> index 3982575bb586..a397b072a580 100644
> --- a/arch/s390/include/asm/pgtable.h
> +++ b/arch/s390/include/asm/pgtable.h
> @@ -181,6 +181,8 @@ static inline int is_module_addr(void *addr)
>  #define _PAGE_SOFT_DIRTY 0x000
>  #endif
>  
> +#define _PAGE_SWP_EXCLUSIVE _PAGE_LARGE	/* SW pte exclusive swap bit */
> +
>  /* Set of bits not changed in pte_modify */
>  #define _PAGE_CHG_MASK		(PAGE_MASK | _PAGE_SPECIAL | _PAGE_DIRTY | \
>  				 _PAGE_YOUNG | _PAGE_SOFT_DIRTY)
> @@ -826,6 +828,22 @@ static inline int pmd_protnone(pmd_t pmd)
>  }
>  #endif
>  
> +#define __HAVE_ARCH_PTE_SWP_EXCLUSIVE
> +static inline int pte_swp_exclusive(pte_t pte)
> +{
> +	return pte_val(pte) & _PAGE_SWP_EXCLUSIVE;
> +}
> +
> +static inline pte_t pte_swp_mkexclusive(pte_t pte)
> +{
> +	return set_pte_bit(pte, __pgprot(_PAGE_SWP_EXCLUSIVE));
> +}
> +
> +static inline pte_t pte_swp_clear_exclusive(pte_t pte)
> +{
> +	return clear_pte_bit(pte, __pgprot(_PAGE_SWP_EXCLUSIVE));
> +}
> +
>  static inline int pte_soft_dirty(pte_t pte)
>  {
>  	return pte_val(pte) & _PAGE_SOFT_DIRTY;
> @@ -1715,14 +1733,15 @@ static inline int has_transparent_hugepage(void)
>   * Bits 54 and 63 are used to indicate the page type. Bit 53 marks the pte
>   * as invalid.
>   * A swap pte is indicated by bit pattern (pte & 0x201) == 0x200
> - * |			  offset			|X11XX|type |S0|
> + * |			  offset			|E11XX|type |S0|
>   * |0000000000111111111122222222223333333333444444444455|55555|55566|66|
>   * |0123456789012345678901234567890123456789012345678901|23456|78901|23|
>   *
>   * Bits 0-51 store the offset.
> + * Bit 52 (E) is used to remember PG_anon_exclusive.
>   * Bits 57-61 store the type.
>   * Bit 62 (S) is used for softdirty tracking.
> - * Bits 52, 55 and 56 (X) are unused.
> + * Bits 55 and 56 (X) are unused.
>   */
>  
>  #define __SWP_OFFSET_MASK	((1UL << 52) - 1)

Thanks David!

Reviewed-by: Gerald Schaefer <[email-masked]>