linux-kernel - Re: [PATCH v2 11/11] powerpc/8xx: Add support for TASK

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Date:	Tue, 07 Apr 2015 10:15:59 +0200
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: [PATCH v2 11/11] powerpc/8xx: Add support for TASK_SIZE greater
 than 0x80000000


Le 21/03/2015 01:47, Scott Wood a écrit :
> On Tue, 2015-01-20 at 10:57 +0100, Christophe Leroy wrote:
>> By default, TASK_SIZE is set to 0x80000000 for PPC_8xx, which is most likely
>> sufficient for most cases. However, kernel configuration allows to set TASK_SIZE
>> to another value, so the 8xx shall handle it.
>>
>> Signed-off-by: Christophe Leroy <christophe.leroy@....fr>
>>
>> ---
>> v2: no change
>>
>>   arch/powerpc/kernel/head_8xx.S | 25 +++++++++++++++++++------
>>   1 file changed, 19 insertions(+), 6 deletions(-)
>>
>> diff --git a/arch/powerpc/kernel/head_8xx.S b/arch/powerpc/kernel/head_8xx.S
>> index ead6448..92a6456 100644
>> --- a/arch/powerpc/kernel/head_8xx.S
>> +++ b/arch/powerpc/kernel/head_8xx.S
>> @@ -48,6 +48,19 @@
>>   	mtspr	spr, reg
>>   #endif
>>   
>> +/* Macro to test if an address is a kernel address */
>> +#if CONFIG_TASK_SIZE <= 0x80000000
>> +#define IS_KERNEL(tmp, addr)		\
>> +	andis.	tmp, addr, 0x8000	/* Address >= 0x80000000 */
>> +#define BRANCH_UNLESS_KERNEL(label)	beq	label
>> +#else
> This works if CONFIG_TASK_SIZE == 0x80000000, but what if it's less, and
> you have a kernel address < 0x80000000?
>
>
You are right, I didn't realise that PAGE_OFFSET was also configurable 
and could be different from 0xC0000000.
andis. (which is what is always used in the current kernel) can be used 
if CONFIG_TASK_SIZE <= 0x80000000 AND PAGE_OFFSET >= 0x80000000.
I will resubmit the patch accordingly.

Christophe

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