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