Re: 2.6.21-rc5-mm3 - no boot, "address not 2M aligned"

thunder7
2007-04-02T11:18:17Z

From: Vivek Goyal <vgoyal@in.ibm.com>
Date: Mon, Apr 02, 2007 at 01:11:59PM +0530
>
> How about attached patch?
>
> o X86_64 kernel should run from 2MB aligned address for two reasons.
> - Performance.
> - For relocatable kernels, page tables are updated based on difference
> between compile time address and load time physical address.
> This difference should be multiple of 2MB as kernel text and data
> is mapped using 2MB pages and PMD should be pointing to a 2MB
> aligned address. Life is simpler if both compile time and load time
> kernel addresses are 2MB aligned.
>
> o Flag the error at compile time if one is trying to build a kernel which
> does not meet alignment restrictions.
>
> Signed-off-by: Vivek Goyal <vgoyal@in.ibm.com>
> ---
>
> arch/x86_64/kernel/head64.c | 8 ++++++++
> include/asm-x86_64/page.h | 1 +
> 2 files changed, 9 insertions(+)
>
> diff -puN arch/x86_64/kernel/head64.c~x86_64-check-for-config-physical-start-aligned-2M arch/x86_64/kernel/head64.c
> --- linux-2.6.21-rc5-mm3-vanilla/arch/x86_64/kernel/head64.c~x86_64-check-for-config-physical-start-aligned-2M 2007-04-02 20:46:43.000000000 +0530
> +++ linux-2.6.21-rc5-mm3-vanilla-root/arch/x86_64/kernel/head64.c 2007-04-02 21:20:45.000000000 +0530
> @@ -62,6 +62,14 @@ void __init x86_64_start_kernel(char * r
> {
> int i;
>
> + /*
> + * Make sure kernel is aligned to 2MB address. Catching it at compile
> + * time is better. Change your config file and compile the kernel
> + * for a 2MB aligned address (CONFIG_PHYSICAL_START)
> + */
> + BUILD_BUG_ON(ALIGN(CONFIG_PHYSICAL_START, __KERNEL_ALIGN)
> + != CONFIG_PHYSICAL_START);
> +
> /* clear bss before set_intr_gate with early_idt_handler */
> clear_bss();
>
> diff -puN include/asm-x86_64/page.h~x86_64-check-for-config-physical-start-aligned-2M include/asm-x86_64/page.h
> --- linux-2.6.21-rc5-mm3-vanilla/include/asm-x86_64/page.h~x86_64-check-for-config-physical-start-aligned-2M 2007-04-02 20:50:55.000000000 +0530
> +++ linux-2.6.21-rc5-mm3-vanilla-root/include/asm-x86_64/page.h 2007-04-02 20:51:34.000000000 +0530
> @@ -79,6 +79,7 @@ extern unsigned long phys_base;
> #endif /* !__ASSEMBLY__ */
>
> #define __PHYSICAL_START CONFIG_PHYSICAL_START
> +#define __KERNEL_ALIGN 0x200000
> #define __START_KERNEL (__START_KERNEL_map + __PHYSICAL_START)
> #define __START_KERNEL_map 0xffffffff80000000
> #define __PAGE_OFFSET 0xffff810000000000
> _

I'm only a user, so I'm not uptodate on these addresses and how they
work. However, how does this solve the problem that running

make oldconfig

on a working 2.6.21-rc3-mm2 .config gives an unbootable 2.6.21-rc5-mm3
kernel? If I read things correctly, you now get a BUG, but the kernel
still won't boot. If that is correct, than I, as a user, don't think
that this is the solution that I feel comfortable with.

If the kernel only boots CONFIG_PHYSICAL_START is aligned on a 2MB
address, then we should align it, not BUG out when it's not, and
especially not when it's unaligned through no fault of the user.

Kind regards,
Jurriaan
--
Debian (Unstable) GNU/Linux 2.6.21-rc5-mm3 2x2010 bogomips load 0.89
the Jack Vance Integral Edition: http://www.integralarchive.org