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

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Date:   Tue, 6 Jun 2023 21:49:00 +0800
From:   "bibo, mao" <maobibo@...ngson.cn>
To:     loongson-kernel@...ts.loongnix.cn,
        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
Subject: Re: [PATCH] LoongArch: let pmd_present return true when splitting pmd

I do not object to adding sw bit for _PAGE_PRESENT_INVALID,  only that can it use
bit12--bit20 since it is for pmd entry only?

Regards
Bibo, Mao

在 2023/6/6 19:38, Hongchen Zhang 写道:
> 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
> 
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