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

["bibo, mao" <maobibo@loongson.cn>]

在 2023/6/8 09:31, Hongchen Zhang 写道:
> Hi Bibo & Anshuman,
> 
> On 2023/6/6 下午9:49, bibo, mao wrote:
>> 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?
> If we change from bit60 to bit12, pmd_pfn will return an incorrect pfn, and it seems that modifying pmd_pfn accordingly is not a good idea.
Good catch. Do you test it or just doubt about it by reviewing the code? bit 12 _PAGE_HGLOBAL_SHIFT is already used by pmd entry. There should be problem also.

if you worry about it, pmd_pfn should be something like x86
static inline pmdval_t pmd_pfn_mask(pmd_t pmd)
{
        if (native_pmd_val(pmd) & _PAGE_PSE)
                return PHYSICAL_PMD_PAGE_MASK;
        else
                return PTE_PFN_MASK;
}

However I think forcefully using bit  60 is not good way. It solves one issue and brings out another problem.

Regards
Bibo, Mao

> 
> Hi Anshuman,
>   What's your opinion about this suggestion? I think arm64 architecture  has similar problems. Why do you choose bit59 instead of bit12--bit20?
>>
>> 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@loongson.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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>>
>>
> 
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