Memory size and section boundary on armv7

[Ilias Apalodimas <ilias.apalodimas@linaro.org>]

Hello, 

While experimenting with u-boot and booting the kernel as an EFI stub i seem to
hit an issue with memory mapping (map_lowmem).

I can only reproduce the crash when using u-boot's dtb (specified in
fdtcontroladdr) and pass that to the kernel, instead of loading an external one
with 'dtb=' on it's command line.

If CONFIG_ARM_LPAE=y, everything works fine. If the latter is not selected
though the kernel seems to crash only if dtb is placed on a section boundary.
The reason is crashes is the BUG_ON() on arm_pte_alloc() triggers.

fdt size is 0xc00 in both scenarios.
So something like this works fine:
In this case ff000 + c000 + f5000 = 200000
[    0.000000] MAP addr: c7c00000, next c7e00000, phys c7c00000 len 200000
[    0.000000] INI addr: c7e00000, next c7eff000, len ff000
[    0.000000] INI addr: c7f0b000, next c8000000, len f5000
[    0.000000] MAP addr: c8000000, next c8200000, phys c8000000 len 200000

In this working case kernel maps sizes ff000 and f5000 alloc_init_pte() and
skips the 0xc000 of the fdt correctly

The non-working case is: 
[    0.000000] MAP addr: c7e00000, next c7f00000, phys c7e00000 len 100000
[    0.000000] INI addr: c7f0c000, next c8000000, len f4000

Both entries end up using the same pmd

I am not sure what's the best way to fix that. 
Obviously skipping the alloc_init_pte() once this case is detected fixes things,
but  is there a better idea?


Thanks
/Ilias

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