Re: [v2 PATCH 1/2] powerpc32: adds handling of _PAGE_RO

[leroy christophe]

Le 18/12/2014 03:14, Scott Wood a Ãcrit :
> On Wed, 2014-12-17 at 10:14 +0100, Christophe Leroy wrote:
> > Some powerpc like the 8xx don't have a RW bit in PTE bits but a RO (Read Only) bit.
> > This patch implements the handling of a _PAGE_RO flag to be used in place of _PAGE_RW
> >
> > Signed-off-by: Christophe Leroy <christophe.leroy@xxxxxx>
> >
> > ---
> > v2 is a complete rework compared to v1
> >
> >   arch/powerpc/include/asm/pgtable-ppc32.h | 11 ++++++-----
> >   arch/powerpc/include/asm/pgtable.h       | 10 +++++++---
> >   arch/powerpc/include/asm/pte-common.h    | 27 ++++++++++++++++++---------
> >   arch/powerpc/mm/gup.c                    |  2 ++
> >   arch/powerpc/mm/mem.c                    |  2 +-
> >   arch/powerpc/mm/pgtable_32.c             | 24 ++++++++++++++++++++----
> >   6 files changed, 54 insertions(+), 22 deletions(-)
> >
> > diff --git a/arch/powerpc/include/asm/pgtable-ppc32.h b/arch/powerpc/include/asm/pgtable-ppc32.h
> > index 543bb8e..64ed9e1 100644
> > --- a/arch/powerpc/include/asm/pgtable-ppc32.h
> > +++ b/arch/powerpc/include/asm/pgtable-ppc32.h
> > @@ -125,7 +125,7 @@ extern int icache_44x_need_flush;
> >   #ifndef __ASSEMBLY__
> >   
> >   #define pte_clear(mm, addr, ptep) \
> > -	do { pte_update(ptep, ~_PAGE_HASHPTE, 0); } while (0)
> > +	do { pte_update(ptep, ~_PAGE_HASHPTE, _PAGE_RO); } while (0)
> Is this really necessary?  It's already clearing the valid bit.
>
> Likewise in several other places that set or check for _PAGE_RO on pages
> for which no access is permitted.
You are right, this is not needed. I needed it because I had defined 
pte_none() as requiring _PAGE_RO set. But we can keep value 0 as 
pte_none. Taken into account in v3

Christophe
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