Re: 2.6.15-mm4 failure on power5

[Michael Ellerman <michael@ellerman.id.au>]

On Mon, 16 Jan 2006 18:05, Andrew Morton wrote:
> "Serge E. Hallyn" <serue@us.ibm.com> wrote:
> > On my power5 partition, 2.6.15-mm4 hangs on boot
>
> It might be worth reverting the changes to arch/powerpc/mm/hash_utils_64.c,
> see if that unbreaks it.
>
> -		base = lmb.memory.region[i].base + KERNELBASE;
> +		base = (unsigned long)__va(lmb.memory.region[i].base);

You can try it, but if that fixes the problem I'll buy a sombrero and then eat 
it.

> The nice comment in page.h:
>
>  * KERNELBASE is the virtual address of the start of the kernel, it's often
>  * the same as PAGE_OFFSET, but _might not be_.
>  *
>  * The kdump dump kernel is one example where KERNELBASE != PAGE_OFFSET.
>  *
>  * To get a physical address from a virtual one you subtract PAGE_OFFSET,
>  * _not_ KERNELBASE.
>
> Tells us that was not an equivalent transformation.

True, not equivalent in all cases, but correct. For non-kdump kernels (which I 
assume this is) KERNELBASE == PAGE_OFFSET, and for a kdump kernel that code 
wants to use PAGE_OFFSET, not KERNELBASE.

Try enabling early debugging (see arch/powerpc/kernel/setup_64.c) and then 
turning on DEBUG in hash_utils_64.c, setup_64.c etc.

cheers

-- 
Michael Ellerman
IBM OzLabs

email: michael:ellerman.id.au
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