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Date:	Mon, 22 Dec 2014 11:25:39 +0100
From:	leroy christophe <christophe.leroy@....fr>
To:	Scott Wood <scottwood@...escale.com>
CC:	Benjamin Herrenschmidt <benh@...nel.crashing.org>,
	Paul Mackerras <paulus@...ba.org>,
	Michael Ellerman <mpe@...erman.id.au>,
	linux-kernel@...r.kernel.org, linuxppc-dev@...ts.ozlabs.org,
	Joakim Tjernlund <joakim.tjernlund@...nsmode.se>
Subject: Re: [v2 PATCH 1/2] powerpc32: adds handling of _PAGE_RO


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@....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.
>
>
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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