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last 256MB of the linux 32bit addresses space on p4080ds arch

Question asked by yoav rubin on Oct 28, 2019
Latest reply on Oct 31, 2019 by yoav rubin

I'm using 32bit linux 4.1.8 with Yocto environment on the P4080DS SoC and noticed that the last 256MB of the 32bit addresses space are reserved for some purpose.

 

from arch/powerpc/mm/init_32.c:

/*The amount of lowmem must be within 0xF0000000 - KERNELBASE. */

# if  (CONFIG_LOWMEM_SIZE > (0xF0000000 - PAGE_OFFSET))

# error "You must adjust CONFIG_LOWMEM_SIZE or CONFIG_KERNEL_START"

# endif

 

I wanted to use addresses 0XF0000000 - 0XFFFFFFFF for lowmemory but I can't.

What are they reserved for? maybe vmalloc area?  and is it possible to resize this reserved area (shrink it)?

 

thanks..

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