linux-kernel - Re: [PATCH] ARM: update __swp_entry_to_pte() to use PTE_TYPE

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Message-ID: <d28673fc-14db-dfd9-6d20-049807891b2e@arm.com>
Date:   Mon, 17 May 2021 13:17:29 +0530
From:   Anshuman Khandual <anshuman.khandual@....com>
To:     Russell King <rmk+kernel@...linux.org.uk>,
        linux-arm-kernel@...ts.infradead.org
Cc:     Thomas Gleixner <tglx@...utronix.de>,
        Allison Randal <allison@...utok.net>,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] ARM: update __swp_entry_to_pte() to use PTE_TYPE_FAULT



On 5/13/21 4:57 PM, Russell King wrote:
> Swap entries use a faulting PTE which have the least two significant
> bits as zero. Due to this, the use of PTE_TYPE_FAULT was overlooked,
> but really should have been included in __swp_entry_to_pte().
> 
> Convert this macro to use PTE_TYPE_FAULT to properly document what is
> going on here, and use __pte() to convert the swp_entry_t to a pte_t.
> 
> This results in no change to the resulting kernel text.
> 
> Signed-off-by: Russell King <rmk+kernel@...linux.org.uk>
> ---
>  arch/arm/include/asm/pgtable.h | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/arch/arm/include/asm/pgtable.h b/arch/arm/include/asm/pgtable.h
> index c02f24400369..c43e07d6046d 100644
> --- a/arch/arm/include/asm/pgtable.h
> +++ b/arch/arm/include/asm/pgtable.h
> @@ -303,7 +303,7 @@ static inline pte_t pte_modify(pte_t pte, pgprot_t newprot)
>  #define __swp_entry(type,offset) ((swp_entry_t) { ((type) << __SWP_TYPE_SHIFT) | ((offset) << __SWP_OFFSET_SHIFT) })
>  
>  #define __pte_to_swp_entry(pte)	((swp_entry_t) { pte_val(pte) })
> -#define __swp_entry_to_pte(swp)	((pte_t) { (swp).val })
> +#define __swp_entry_to_pte(swp)	__pte((swp).val | PTE_TYPE_FAULT)

LGTM and FWIW..

Reviewed-by: Anshuman Khandual <anshuman.khandual@....com>

>  
>  /*
>   * It is an error for the kernel to have more swap files than we can
>