Messages in this thread | | | Date | Thu, 18 Dec 2014 08:11:26 +0100 | From | leroy christophe <> | Subject | Re: [v2 PATCH 1/2] powerpc32: adds handling of _PAGE_RO |
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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.leroy@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.
Christophe
> > pte_update(ptep, clr, set); > > -Scott >
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