linux-kernel - Re: [PATCHv7 11/19] x86/mm: Make STACK_TOP

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Message-ID: <20170928082955.n7t4wlz7olsgwkfn@gmail.com>
Date:   Thu, 28 Sep 2017 10:29:55 +0200
From:   Ingo Molnar <mingo@...nel.org>
To:     "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>
Cc:     Ingo Molnar <mingo@...hat.com>,
        Linus Torvalds <torvalds@...ux-foundation.org>, x86@...nel.org,
        Thomas Gleixner <tglx@...utronix.de>,
        "H. Peter Anvin" <hpa@...or.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Andy Lutomirski <luto@...capital.net>,
        Cyrill Gorcunov <gorcunov@...nvz.org>,
        Borislav Petkov <bp@...e.de>, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCHv7 11/19] x86/mm: Make STACK_TOP_MAX dynamic


* Kirill A. Shutemov <kirill.shutemov@...ux.intel.com> wrote:

> For boot-time switching between paging modes, we need to be able to
> change STACK_TOP_MAX at runtime.
> 
> The change is trivial and it doesn't affect kernel image size.
> 
> Signed-off-by: Kirill A. Shutemov <kirill.shutemov@...ux.intel.com>
> ---
>  arch/x86/include/asm/processor.h | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/arch/x86/include/asm/processor.h b/arch/x86/include/asm/processor.h
> index 3fa26a61eabc..fa9300ccce1b 100644
> --- a/arch/x86/include/asm/processor.h
> +++ b/arch/x86/include/asm/processor.h
> @@ -871,7 +871,7 @@ static inline void spin_lock_prefetch(const void *x)
>  					IA32_PAGE_OFFSET : TASK_SIZE_MAX)
>  
>  #define STACK_TOP		TASK_SIZE_LOW
> -#define STACK_TOP_MAX		TASK_SIZE_MAX
> +#define STACK_TOP_MAX		(pgtable_l5_enabled ? TASK_SIZE_MAX : DEFAULT_MAP_WINDOW)

While it's only used once in fs/exec.c, why doesn't it affect kernel image size?

Thanks,

	Ingo