Comment 13 for bug 219868

I can confirm that this is an upstream bug in the Linux kernel and still affects all kernels up to and including 2.6.38.*. A fix has now been merged into 2.6.39 but it's a very trivial single letter change.

The git commit is 39b68976ac653cfdc7f872a293e8b7928de2dcc6 in Linus's mainline tree and H. Peter Anvin describes it as:

# When we use BIOS function e801 to probe memory, we should use ax/bx
# (or cx/dx) as a pair, not mix and match. This was a typo during the
# translation from assembly code, and breaks at least one set of
# machines in the field (which return cx = dx = 0).

The commit in Linus's tree is here:

http://git.kernel.org/?p=linux/kernel/git/torvalds/linux-2.6.git;a=commit;h=39b68976ac653cfdc7f872a293e8b7928de2dcc6

Hope this helps!