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

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Date:	Mon, 8 Feb 2016 10:11:34 -0800
From:	David Daney <ddaney@...iumnetworks.com>
To:	Harvey Hunt <harvey.hunt@...tec.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

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.

>   #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.

>   #define TASK_SIZE64	0x10000000000UL
>   #define TASK_SIZE (test_thread_flag(TIF_32BIT_ADDR) ? TASK_SIZE32 : TASK_SIZE64)
>   #define STACK_TOP_MAX	TASK_SIZE64
>