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;
pte_update(ptep, clr, set);
-Scott
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