405GPr ioremap problem

Hi, folks

I have a 405GPr based board with 512M of RAM.
My kernel is 2.4.17 from Monta Vista Linux 2.1.
I'm  trying to reserve 64M on boot using mem=448M
and map it later by

ioremap(__pa(high_memory), 64*(1<<20));

This worked fine when system had 256M of RAM,
but now ioremap fails. If I understand the kernel
code correctly, by adding more RAM I've reduced
the vmalloc/ioremap space. I can also see that this
space is reduced dramatically on boot by mappings
done in arch/ppc/kernel/ppc4xx_setup.c:m4xx_map_io()

Is there any way to fix problem ? Is it necessary to have
a 1:1 virtual to physical mappings as its done in m4xx_map_io()
or maybe higher virtual addresses can be used, thus
allowing to save some precious ioremap space.

Thanks a lot in advance.

Please CC me, as I'm not on the list.

Felix.