Re: [PATCH] MIPS: fix pmd_mkinvalid

[Hongchen Zhang]

On 2022/5/31 下午11:40, Jiaxun Yang wrote:
> 在 2022/5/31 5:36, Hongchen Zhang 写道:
> > pmd_mkinvalid should not clear dirty flag,otherwise the pmd
> > dirty flag,it's ok to just clear _PAGE_VALID.
> Hi Hongcheng,
>
> Sorry, what is meant by "otherwise the pmd dirty flag"? Could you please
> elaborate?
> In my humble opinion _PAGE_PRESENT must be cleared in mkinvalid as it
> nolonger present here. And thus it lose the dirty status.
>
> Thanks
> - Jiaxun
>
> > Signed-off-by: Hongchen Zhang <zhanghongchen@xxxxxxxxxxx>
> > ---
> >   arch/mips/include/asm/pgtable.h | 2 +-
> >   1 file changed, 1 insertion(+), 1 deletion(-)
> >
> > diff --git a/arch/mips/include/asm/pgtable.h 
> > b/arch/mips/include/asm/pgtable.h
> > index 374c632..d30a186 100644
> > --- a/arch/mips/include/asm/pgtable.h
> > +++ b/arch/mips/include/asm/pgtable.h
> > @@ -698,7 +698,7 @@ 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 | _PAGE_VALID | _PAGE_DIRTY);
> > +    pmd_val(pmd) &= ~_PAGE_VALID;
> >       return pmd;
> >   }
Hi Jiaxun,

Refer to [ https://lkml.org/lkml/2018/10/17/231 ],Andrea said "
The clear of the real present bit during pmd (virtual) splitting is
done with pmdp_invalidate, that is created specifically to keeps
pmd_trans_huge=true, pmd_present=true despite the present bit is not
set. ". So it's wrong to clear _PAGE_PRESENT,because this will make 
pmd_present=false.

On the other hand, There is no need to clear dirty flag too.

Thanks.