linux-kernel - Re: [PATCH v2 7/8] powerpc/pgtable: remove _PAGE_BIT_SWAP

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Message-ID: <22d3c42d-402f-8aeb-e989-c05d023b2ed3@csgroup.eu>
Date:   Wed, 30 Mar 2022 06:07:22 +0000
From:   Christophe Leroy <christophe.leroy@...roup.eu>
To:     David Hildenbrand <david@...hat.com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
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Subject: Re: [PATCH v2 7/8] powerpc/pgtable: remove _PAGE_BIT_SWAP_TYPE for
 book3s



Le 29/03/2022 à 18:43, David Hildenbrand a écrit :
> The swap type is simply stored in bits 0x1f of the swap pte. Let's
> simplify by just getting rid of _PAGE_BIT_SWAP_TYPE. It's not like that
> we can simply change it: _PAGE_SWP_SOFT_DIRTY would suddenly fall into
> _RPAGE_RSV1, which isn't possible and would make the
> BUILD_BUG_ON(_PAGE_HPTEFLAGS & _PAGE_SWP_SOFT_DIRTY) angry.
> 
> While at it, make it clearer which bit we're actually using for
> _PAGE_SWP_SOFT_DIRTY by just using the proper define and introduce and
> use SWP_TYPE_MASK.
> 
> Signed-off-by: David Hildenbrand <david@...hat.com>
> ---
>   arch/powerpc/include/asm/book3s/64/pgtable.h | 12 +++++-------

Why only BOOK3S ? Why not BOOK3E as well ?

Christophe

>   1 file changed, 5 insertions(+), 7 deletions(-)
> 
> diff --git a/arch/powerpc/include/asm/book3s/64/pgtable.h b/arch/powerpc/include/asm/book3s/64/pgtable.h
> index 875730d5af40..8e98375d5c4a 100644
> --- a/arch/powerpc/include/asm/book3s/64/pgtable.h
> +++ b/arch/powerpc/include/asm/book3s/64/pgtable.h
> @@ -13,7 +13,6 @@
>   /*
>    * Common bits between hash and Radix page table
>    */
> -#define _PAGE_BIT_SWAP_TYPE	0
>   
>   #define _PAGE_EXEC		0x00001 /* execute permission */
>   #define _PAGE_WRITE		0x00002 /* write access allowed */
> @@ -751,17 +750,16 @@ static inline pte_t pte_modify(pte_t pte, pgprot_t newprot)
>   	 * Don't have overlapping bits with _PAGE_HPTEFLAGS	\
>   	 * We filter HPTEFLAGS on set_pte.			\
>   	 */							\
> -	BUILD_BUG_ON(_PAGE_HPTEFLAGS & (0x1f << _PAGE_BIT_SWAP_TYPE)); \
> +	BUILD_BUG_ON(_PAGE_HPTEFLAGS & SWP_TYPE_MASK); \
>   	BUILD_BUG_ON(_PAGE_HPTEFLAGS & _PAGE_SWP_SOFT_DIRTY);	\
>   	} while (0)
>   
>   #define SWP_TYPE_BITS 5
> -#define __swp_type(x)		(((x).val >> _PAGE_BIT_SWAP_TYPE) \
> -				& ((1UL << SWP_TYPE_BITS) - 1))
> +#define SWP_TYPE_MASK		((1UL << SWP_TYPE_BITS) - 1)
> +#define __swp_type(x)		((x).val & SWP_TYPE_MASK)
>   #define __swp_offset(x)		(((x).val & PTE_RPN_MASK) >> PAGE_SHIFT)
>   #define __swp_entry(type, offset)	((swp_entry_t) { \
> -				((type) << _PAGE_BIT_SWAP_TYPE) \
> -				| (((offset) << PAGE_SHIFT) & PTE_RPN_MASK)})
> +				(type) | (((offset) << PAGE_SHIFT) & PTE_RPN_MASK)})
>   /*
>    * swp_entry_t must be independent of pte bits. We build a swp_entry_t from
>    * swap type and offset we get from swap and convert that to pte to find a
> @@ -774,7 +772,7 @@ static inline pte_t pte_modify(pte_t pte, pgprot_t newprot)
>   #define __swp_entry_to_pmd(x)	(pte_pmd(__swp_entry_to_pte(x)))
>   
>   #ifdef CONFIG_MEM_SOFT_DIRTY
> -#define _PAGE_SWP_SOFT_DIRTY   (1UL << (SWP_TYPE_BITS + _PAGE_BIT_SWAP_TYPE))
> +#define _PAGE_SWP_SOFT_DIRTY	_PAGE_NON_IDEMPOTENT
>   #else
>   #define _PAGE_SWP_SOFT_DIRTY	0UL
>   #endif /* CONFIG_MEM_SOFT_DIRTY */