crazyscot

Mm. We should arguably handle that case better - the problem is that without the MTRR coverage, accesses to that memory end up uncached. Guess how well that works. Trimming the memory down to the MTRR range at least lets people use the machine well enough to find a BIOS upgrade.

Previous attempts to reconfigure the mtrr layout have tended to end quite badly, with all kinds of unexpected interactions with the BIOS (there aren't enough MTRRs to avoid every hole in memory, but how do we tell if the BIOS expects a specific area of reserved address space to be uncached?). Moving to using PAT instead might work better, but then we end up with the pretty much entirely undocumented semantics of what happens when you have conflicting MTRR and PAT configurations. Have I ever mentioned that everything involving firmware is dreadful?