RE: locking user memory and kiobuf

Bret Indrelee (bindrelee@sbs-cp.com)
Mon, 8 Nov 1999 13:20:07 -0600

Jeff Garzik [mailto:jgarzik@mandrakesoft.com] wrote:
> Bret Indrelee wrote:
> > Does page_address() return a virtual or physical address?
> > To me it looks
> > like it may be a physical address, in which case you would
> > have to do:
> > memcpy (foo, phys_to_virt(phys), PAGE_SIZE *4);
>
> Not true. The above code example was in kernel space, and
> the memcpy is
> definitely in kernel (physical) address space as well.

Kernel address space is different than physical address space.

Kernel address space is a virtual address that goes through the MMU (page
tables) in order to create the physical address. Virtual address space is as
seen from the CPU, physical address space is as seen with a logic analyzer
hooked up to the board traces.

It may be that some of the kernel address space is mapped to the identical
physical address space, I don't know if Linux does this or not. The MIPS
chip has a section of its address space that is direct mapped.

-Bret

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