Two year old bug bites Linux users

An almost two-year old bug in AMD's Athlon and Duron processors has been found to trip up Linux users.

Users of the 2.4 kernel have been informed that a problem exists in the Accelerated Graphics Port (AGP) video functionality when used in conjunction with an Athlon or Duron processor.

The problem is that x86 systems have typically managed memory in 4Kb pages, but when the Pentium processor was introduced Intel added a feature called extended paging which allowed 4Mb pages to be used instead.

The Linux 2.4 kernel automatically takes advantage of extended paging by running Pentium specific instructions. The result is that Athlon and Duron processors experience memory corruption when using AGP video.

Although the problem is a processor rather than a Linux bug, a quick workaround is at hand. Passing the line 'append mem=nopentium' when booting up will disable all Pentium specific instructions and thus solve the problem.

The bug has been known about since September 2000 when Microsoft issued a patch for a similar problem on the Windows 2000 operating system. At the time AMD released a fix for Windows 2000 that disabled extended paging.

But it seems that the chip giant overlooked the fact that the problem would also manifest itself when the Linux 2.4 kernel is compiled with a Pentium Classic or higher processor family kernel configuration setting.

Linux news site Gentoo has more details available.