On Thu, 2014-12-18 at 08:11 +0100, leroy christophe wrote:
> Le 18/12/2014 03:14, Scott Wood a écrit :
> > 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.le...@c-s.fr>
> >>
> >> ---
> >> 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.
> >
> >> @@ -287,8 +287,9 @@ static inline void huge_ptep_set_wrprotect(struct
> >> mm_struct *mm,
> >> static inline void __ptep_set_access_flags(pte_t *ptep, pte_t entry)
> >> {
> >> unsigned long bits = pte_val(entry) &
> >> - (_PAGE_DIRTY | _PAGE_ACCESSED | _PAGE_RW | _PAGE_EXEC);
> >> - pte_update(ptep, 0, bits);
> >> + (_PAGE_DIRTY | _PAGE_ACCESSED | _PAGE_RW | _PAGE_RO |
> >> + _PAGE_EXEC);
> >> + pte_update(ptep, _PAGE_RO, bits);
> >> }
> > You're unconditionally clearing _PAGE_RO, and apparently relying on the
> > undocumented behavior of pte_update() to clear "clr" before setting
> > "set".
> >
> > Instead I'd write this as:
> >
> > unsigned long set = pte_val(entry) &
> > (_PAGE_DIRTY | _PAGE_ACCESSED | _PAGE_RW | _PAGE_EXEC);
> > unsigned long clr = pte_val(entry) & _PAGE_RO;
> Don't you mean ?
>
> unsigned long clr = ~pte_val(entry) & _PAGE_RO;
>
> Because, we want to clear _PAGE_RO when _PAGE_RO is not set in entry.
Yes, sorry.
-Scott
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