linux-kernel - Re: [PATCH] MIPS: Always page align TASK

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Date:	Mon, 8 Feb 2016 13:48:32 -0800
From:	Harvey Hunt <harvey.hunt@...tec.com>
To:	Joshua Kinard <kumba@...too.org>,
	David Daney <ddaney@...iumnetworks.com>
CC:	<linux-mips@...ux-mips.org>, <ralf@...ux-mips.org>,
	David Daney <david.daney@...ium.com>,
	Paul Burton <paul.burton@...tec.com>,
	James Hogan <james.hogan@...tec.com>,
	<linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] MIPS: Always page align TASK_SIZE

Hi Joshua,

On 02/08/2016 01:35 PM, Joshua Kinard wrote:
> On 02/08/2016 13:15, Harvey Hunt wrote:
>> Hi David,
>>
>> On 02/08/2016 10:11 AM, David Daney wrote:
>>> On 02/08/2016 10:05 AM, Harvey Hunt wrote:
>>>> STACK_TOP_MAX is aligned on a 32k boundary. When __bprm_mm_init()
>>>> creates an
>>>> initial stack for a process, it does so using STACK_TOP_MAX as the end
>>>> of the
>>>> vma. A process's arguments and environment information are placed on
>>>> the stack
>>>> and then the stack is relocated and aligned on a page boundary. When
>>>> using a 32
>>>> bit kernel with 64k pages, the relocated stack has the process's args
>>>> erroneously stored in the middle of the stack. This means that processes
>>>> receive no arguments or environment variables, preventing them from
>>>> running
>>>> correctly.
>>>>
>>>> Fix this by aligning TASK_SIZE on a page boundary.
>>>>
>>>> Signed-off-by: Harvey Hunt <harvey.hunt@...tec.com>
>>>> Cc: David Daney <david.daney@...ium.com>
>>>> Cc: Paul Burton <paul.burton@...tec.com>
>>>> Cc: James Hogan <james.hogan@...tec.com>
>>>> Cc: linux-kernel@...r.kernel.org
>>>> ---
>>>>    arch/mips/include/asm/processor.h | 6 +++---
>>>>    1 file changed, 3 insertions(+), 3 deletions(-)
>>>>
>>>> diff --git a/arch/mips/include/asm/processor.h
>>>> b/arch/mips/include/asm/processor.h
>>>> index 3f832c3..b618b40 100644
>>>> --- a/arch/mips/include/asm/processor.h
>>>> +++ b/arch/mips/include/asm/processor.h
>>>> @@ -39,13 +39,13 @@ extern unsigned int vced_count, vcei_count;
>>>>    #ifdef CONFIG_32BIT
>>>>    #ifdef CONFIG_KVM_GUEST
>>>>    /* User space process size is limited to 1GB in KVM Guest Mode */
>>>> -#define TASK_SIZE    0x3fff8000UL
>>>> +#define TASK_SIZE    (0x40000000UL - PAGE_SIZE)
>>>>    #else
>>>>    /*
>>>>     * User space process size: 2GB. This is hardcoded into a few places,
>>>>     * so don't change it unless you know what you are doing.
>>>>     */
>>>> -#define TASK_SIZE    0x7fff8000UL
>>>> +#define TASK_SIZE    (0x7fff8000UL & PAGE_SIZE)
>>>
>>> Can you check your math here.  This doesn't seem correct.
>>
>> Thanks for spotting that - it should have been:
>>
>> (0x7fff8000UL & PAGE_MASK)
>>
>> I'll do a v2 now.
>>
>
> FYI, TASK_SIZE was recently changed to 0x80000000UL in commit 7f8ca9cb1ed3 on
> the linux-mips.org tree.

Thanks, I'll rebase.

>
>
>>>
>>>>    #endif
>>>>
>>>>    #define STACK_TOP_MAX    TASK_SIZE
>>>> @@ -62,7 +62,7 @@ extern unsigned int vced_count, vcei_count;
>>>>     * support 16TB; the architectural reserve for future expansion is
>>>>     * 8192EB ...
>>>>     */
>>>> -#define TASK_SIZE32    0x7fff8000UL
>>>> +#define TASK_SIZE32    (0x7fff8000UL & PAGE_SIZE)
>>>
>>> Same here.
>>
>> As above.
>>
>>>
>>>>    #define TASK_SIZE64    0x10000000000UL
>>>>    #define TASK_SIZE (test_thread_flag(TIF_32BIT_ADDR) ? TASK_SIZE32 :
>>>> TASK_SIZE64)
>>>>    #define STACK_TOP_MAX    TASK_SIZE64
>>>>
>>>
>>
>> Thanks,
>>
>> Harvey
>>
>>
>
>