linux-kernel - Re: [PATCH] LoongArch: let pmd_present return true when splitting pmd

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Date:   Tue, 6 Jun 2023 19:38:38 +0800
From:   Hongchen Zhang <zhanghongchen@...ngson.cn>
To:     Huacai Chen <chenhuacai@...nel.org>,
        WANG Xuerui <kernel@...0n.name>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Anshuman Khandual <anshuman.khandual@....com>,
        David Hildenbrand <david@...hat.com>,
        Mike Rapoport <rppt@...nel.org>,
        Jiaxun Yang <jiaxun.yang@...goat.com>,
        Feiyang Chen <chenfeiyang@...ngson.cn>,
        Qi Zheng <zhengqi.arch@...edance.com>
Cc:     loongarch@...ts.linux.dev, linux-kernel@...r.kernel.org,
        loongson-kernel@...ts.loongnix.cn
Subject: Re: [PATCH] LoongArch: let pmd_present return true when splitting pmd

Hi,

Gentle ping.

On 2023/5/24 pm 3:41, Hongchen Zhang wrote:
> when we split a pmd into ptes, pmd_present() and pmd_trans_huge() should
> return true,otherwise it would be treated as a swap pmd.
> As arm64 does in
> commit b65399f6111b ("arm64/mm: Change THP helpers to comply with generic MM semantics")
> we add a _PAGE_PRESENT_INVALID bit for LoongArch.
> 
> Signed-off-by: Hongchen Zhang <zhanghongchen@...ngson.cn>
> ---
>   arch/loongarch/include/asm/pgtable-bits.h | 2 ++
>   arch/loongarch/include/asm/pgtable.h      | 3 ++-
>   2 files changed, 4 insertions(+), 1 deletion(-)
> 
> diff --git a/arch/loongarch/include/asm/pgtable-bits.h b/arch/loongarch/include/asm/pgtable-bits.h
> index 8b98d22a145b..a7469d28d9d0 100644
> --- a/arch/loongarch/include/asm/pgtable-bits.h
> +++ b/arch/loongarch/include/asm/pgtable-bits.h
> @@ -22,12 +22,14 @@
>   #define	_PAGE_PFN_SHIFT		12
>   #define	_PAGE_SWP_EXCLUSIVE_SHIFT 23
>   #define	_PAGE_PFN_END_SHIFT	48
> +#define _PAGE_PRESENT_INVALID_SHIFT 60
>   #define	_PAGE_NO_READ_SHIFT	61
>   #define	_PAGE_NO_EXEC_SHIFT	62
>   #define	_PAGE_RPLV_SHIFT	63
>   
>   /* Used by software */
>   #define _PAGE_PRESENT		(_ULCAST_(1) << _PAGE_PRESENT_SHIFT)
> +#define _PAGE_PRESENT_INVALID	(_ULCAST_(1) << _PAGE_PRESENT_INVALID_SHIFT)
>   #define _PAGE_WRITE		(_ULCAST_(1) << _PAGE_WRITE_SHIFT)
>   #define _PAGE_ACCESSED		(_ULCAST_(1) << _PAGE_ACCESSED_SHIFT)
>   #define _PAGE_MODIFIED		(_ULCAST_(1) << _PAGE_MODIFIED_SHIFT)
> diff --git a/arch/loongarch/include/asm/pgtable.h b/arch/loongarch/include/asm/pgtable.h
> index d28fb9dbec59..9a9f9ff9b709 100644
> --- a/arch/loongarch/include/asm/pgtable.h
> +++ b/arch/loongarch/include/asm/pgtable.h
> @@ -213,7 +213,7 @@ static inline int pmd_bad(pmd_t pmd)
>   static inline int pmd_present(pmd_t pmd)
>   {
>   	if (unlikely(pmd_val(pmd) & _PAGE_HUGE))
> -		return !!(pmd_val(pmd) & (_PAGE_PRESENT | _PAGE_PROTNONE));
> +		return !!(pmd_val(pmd) & (_PAGE_PRESENT | _PAGE_PROTNONE | _PAGE_PRESENT_INVALID));
>   
>   	return pmd_val(pmd) != (unsigned long)invalid_pte_table;
>   }
> @@ -558,6 +558,7 @@ static inline pmd_t pmd_modify(pmd_t pmd, pgprot_t newprot)
>   
>   static inline pmd_t pmd_mkinvalid(pmd_t pmd)
>   {
> +	pmd_val(pmd) |= _PAGE_PRESENT_INVALID;
>   	pmd_val(pmd) &= ~(_PAGE_PRESENT | _PAGE_VALID | _PAGE_DIRTY | _PAGE_PROTNONE);
>   
>   	return pmd;
> 
> base-commit: f1fcbaa18b28dec10281551dfe6ed3a3ed80e3d6
> 

Best Regards
Hongchen Zhang