Re: How CPU(x86) resolve kernel address

[Joseph A Knapka <jknapka@earthlink.net>]

Sanket Rathi wrote:

> I read all about the memory management in linux. all thing are clear to me
> like there is 3GB space for user procee and 1GB for kernel and thats why
> kernel address always greater then 0xC0000000. But one thing is not clear
> that is for kernel address there is no page table,


Yes there is. Look for swapper_pg_dir. It maps physical address
N to virtual address PAGE_OFFSET+N.

> actually there is no
> need because this is one to one mapping to physical memory but who resolve
> kernel address to actual physical address how CPU(X86) perform this task
> because when we do DMA we have to give actual physical address by
> virt_to_phys() so what is the mechanism by which CPU translate kernel
> address into physical address ( Somewhere i heard that CPU ignore some of
> the upper bits of address if so then how much bits and why).


I don't think so. Kernel and user addresses all pass through
the virtual mapping mechanism. virt_to_phys() just subtracts
PAGE_OFFSET from the kernel virtual address to arrive at the
physical address

Cheers,


-- Joe
   Using open-source software: free.
   Pissing Bill Gates off: priceless.

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