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

[Hongchen Zhang]

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.

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@xxxxxxxxxxx>
> > > ---
> > >    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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