[Barrelfish-users] [Barrelfish] boot page table init on x86-64

Simon Peter speter at inf.ethz.ch
Fri Apr 15 13:44:58 CEST 2011

> In kernel/arch/x86_64/init.c, paging_x86_64_reset() is called in text_init(). paging_x86_64_reset() just maps first megabytes and kernel to MEMORY_OFFSET, however, since those two regions are guaranteed to be included in [0, X86_64_PADDR_SPACE_LIMIT), which is the maximum physical address space, why not just map [0, X86_64_PADDR_SPACE_LIMIT) in paging_x86_64_reset() but instead map those regions first in paging_x86_64_reset() then map the whole physical memory in text_init()?

As the comment above the line that maps until X86_64_PADDR_SPACE_LIMIT 
says, this is just until we have a reliable way to detect and create 
mappings for RAM, after bootup is completed.

What this means is that the line mapping all of X86_64_PADDR_SPACE_LIMIT 
shouldn't be there and the kernel should just be mapping a minimum 
amount of memory that it needs to boot (ie. what it maps in 
paging_x86_64_reset()). After that, a user space program (most likely 
'pci') should do hardware discovery and create additional RAM mappings 
in the kernel.

Feel free to add support for this if you like.


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