A fedora user recently filed a puzzling bug atif there's a hole in the physical address space (for pci devices), you would need more than 32 bits to address 4GB RAM.
https://bugzilla.redhat.com/bugzilla/show_bug.cgi?id=169741
The system being reported has exactly 4GB, and its E820
tables seem to concur that there is in fact 4GB.
When run in non-PAE mode, it triggers the
"Warning only 4GB will be used. Use a PAE enabled kernel."
message, which is odd, but the system does actually run.
When run in PAE mode, it seems to lose its mind, and itlooks like a 1GB hole.
fails to run various binaries.
Booting with mem=4G causes the machine to boot fine
(though for some reason, it finds only 3042M of RAM).
The reporter of this bug has tested on 2.6.14-rc3-git4, and found themaybe the last 1GB is bad. since it can only be accessed by pae, only the pae kernel fails.
same issue exists as he saw on the original FC3 kernel, thus ruling out
any Fedora-specific patches.
Anyone have any ideas what's wrong here?