linux-kernel - Re: [PATCH 17/20] x86_64: Remove CONFIG_PHYSICAL

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Date:	Sat, 18 Nov 2006 10:14:31 +0900
From:	"Magnus Damm" <magnus.damm@...il.com>
To:	vgoyal@...ibm.com
Cc:	"linux kernel mailing list" <linux-kernel@...r.kernel.org>,
	"Reloc Kernel List" <fastboot@...ts.osdl.org>,
	ebiederm@...ssion.com, akpm@...l.org, ak@...e.de, hpa@...or.com,
	lwang@...hat.com, dzickus@...hat.com, pavel@...e.cz, rjw@...k.pl
Subject: Re: [PATCH 17/20] x86_64: Remove CONFIG_PHYSICAL_START

Hi Vivek,

Sorry for not commenting on an earlier version.

On 11/18/06, Vivek Goyal <vgoyal@...ibm.com> wrote:
> I am about to add relocatable kernel support which has essentially
> no cost so there is no point in retaining CONFIG_PHYSICAL_START
> and retaining CONFIG_PHYSICAL_START makes implementation of and
> testing of a relocatable kernel more difficult.
>
> Signed-off-by: Eric W. Biederman <ebiederm@...ssion.com>
> Signed-off-by: Vivek Goyal <vgoyal@...ibm.com>
> ---
>
>  arch/x86_64/Kconfig                |   19 -------------------
>  arch/x86_64/boot/compressed/head.S |    6 +++---
>  arch/x86_64/boot/compressed/misc.c |    6 +++---
>  arch/x86_64/defconfig              |    1 -
>  arch/x86_64/kernel/vmlinux.lds.S   |    2 +-
>  arch/x86_64/mm/fault.c             |    4 ++--
>  include/asm-x86_64/page.h          |    2 --
>  7 files changed, 9 insertions(+), 31 deletions(-)

[snip]

> diff -puN arch/x86_64/mm/fault.c~x86_64-Remove-CONFIG_PHYSICAL_START arch/x86_64/mm/fault.c
> --- linux-2.6.19-rc6-reloc/arch/x86_64/mm/fault.c~x86_64-Remove-CONFIG_PHYSICAL_START   2006-11-17 00:12:50.000000000 -0500
> +++ linux-2.6.19-rc6-reloc-root/arch/x86_64/mm/fault.c  2006-11-17 00:12:50.000000000 -0500
> @@ -644,9 +644,9 @@ void vmalloc_sync_all(void)
>                         start = address + PGDIR_SIZE;
>         }
>         /* Check that there is no need to do the same for the modules area. */
> -       BUILD_BUG_ON(!(MODULES_VADDR > __START_KERNEL));
> +       BUILD_BUG_ON(!(MODULES_VADDR > __START_KERNEL_map));
>         BUILD_BUG_ON(!(((MODULES_END - 1) & PGDIR_MASK) ==
> -                               (__START_KERNEL & PGDIR_MASK)));
> +                               (__START_KERNEL_map & PGDIR_MASK)));
>  }

This code looks either like a bugfix or a bug. If it's a fix then
maybe it should be broken out and submitted separately for the
rc-kernels?

> diff -puN include/asm-x86_64/page.h~x86_64-Remove-CONFIG_PHYSICAL_START include/asm-x86_64/page.h
> --- linux-2.6.19-rc6-reloc/include/asm-x86_64/page.h~x86_64-Remove-CONFIG_PHYSICAL_START        2006-11-17 00:12:50.000000000 -0500
> +++ linux-2.6.19-rc6-reloc-root/include/asm-x86_64/page.h       2006-11-17 00:12:50.000000000 -0500
> @@ -75,8 +75,6 @@ typedef struct { unsigned long pgprot; }
>
>  #endif /* !__ASSEMBLY__ */
>
> -#define __PHYSICAL_START       _AC(CONFIG_PHYSICAL_START,UL)
> -#define __START_KERNEL         (__START_KERNEL_map + __PHYSICAL_START)
>  #define __START_KERNEL_map     _AC(0xffffffff80000000,UL)
>  #define __PAGE_OFFSET           _AC(0xffff810000000000,UL)

I understand that you want to remove the Kconfig option
CONFIG_PHYSICAL_START and that is fine with me. I don't however like
the idea of replacing __PHYSICAL_START and __START_KERNEL with
hardcoded values. Is there any special reason behind this?

The code in page.h already has constants for __START_KERNEL_map and
__PAGE_OFFSET (thank god) and none of them are adjustable via Kconfig.
Why not change as little as possible and keep __PHYSICAL_START and
__START_KERNEL in page.h and the places that use them but remove
references to CONFIG_PHYSICAL_START in Kconfig, defconfig, and page.h?

/ magnus
-
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