Large mmio resources and 4G+ of RAM...

Eric W. Biederman ebiederman at
Tue Jun 1 02:29:01 CEST 2004

Stefan Reinauer <stepan at> writes:

> * Eric W. Biederman <ebiederman at> [040601 08:05]:
> > Looking the large memory mapped I/O resources all have 64bit BARs.  So
> > I am just going to modify the LinuxBIOS resource allocator to put
> > 64bit BARs on x86-64 boxes at least above the top of memory.
> > 
> > There are a couple of short term hacks that I can do with relocating
> > memory but on the Opteron the more memory I add the more problems
> > I run into.  And moving BARS above 4G looks like the right term
> > fix.
> When running a 32bit operating system (like linux/x86) does this mean
> that I am able to see more of my memory, but my pci devices will vanish?

Essentially.  Although the pci devices don't vanish you likely can't use
them because some of their BARS have values that 32bit kernels can't
cope with.  lspci should let you see that though.   A 32bit kernel
with PAE enabled could code but no one has written the code.

I don't have a problem with adding an option to disable this for 32bit
kernels.  I am just tired of optimizing 64bit machines for 32bit

I need to be a little bit careful here as AMD's IO-APICs have 64bit
BARs but are only 4K.  So I might want to put in a size filter.  Plus
I need to ensure the bridges have enough resources to move things.


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