[uml-devel] Physical vs Virtual

[Jon S. <jon...@ya...>]

Just to summarize, a lot of things in the physical
address space are at fixed, well know locations. 
Examples are IO ports, ROMs,  DMA controller, AGP
port, etc. If the address isn't absolutely fixed, it
is controlled by writing an new address to an IO port.

As far as I know, UML doesn't have a way of tracking
memmapping from physical space to kernel virtual
space. This is why I had to add the ioremap code. I
had to record these mappings in the region array but
this might not have been the best place to put them.

Another example of this is the current IOMAP= support.
 To do this the find_iomem UML kernel call was added. 
Instead something like IOMAP=0xPhysicallAddr,file
should have been used.  Then the normal kernel call of
ioremap(0xPhysicalAddr) would have worked. 

I've also got to get it into my head that just because
UML is running on my X86 box, it's not an X86 kernel. 
This means that things things that are standard in the
X86 kernel may not be there in UML (like the 0xA0 -
0X100) mapping.

In general adding support for physical addresses to
UML isn't very hard to do, it's just real confusing to
do it because of all the layers of virtualization.

=====
Jon Smirl
jon...@ya...

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