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

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Date:	Mon, 8 Feb 2016 14:26:43 -0800
From:	Harvey Hunt <harvey.hunt@...tec.com>
To:	David Daney <ddaney@...iumnetworks.com>
CC:	Joshua Kinard <kumba@...too.org>, <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



On 02/08/2016 02:08 PM, David Daney wrote:
> On 02/08/2016 01:48 PM, Harvey Hunt wrote:
>> 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.
>
> You may find that in rebasing, suddenly you have a completely empty patch!
>

Yeah, I noticed that. I'll just drop this patch...

Thanks,

Harvey

>
>>
>>>
>>>
>>>>>
>>>>>>    #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
>>>>
>>>>
>>>
>>>
>