In the Linux kernel, the following vulnerability has been resolved:

x86/amd_node: Avoid divide by zero on virtualized systems

On a virtualized system, the number of nodes does not have a relationship to
the number of roots.  A Xen PVH dom0 can calculate roots_per_node as 0, which
crashes with a divide by zero in:

  if (count++ % roots_per_node)

because the underlying topology code on Xen ends up making num_nodes
2 and num_roots 1 and the integer division result is 0.

The issue is seen with Xen, but it could affect other systems.

Set roots_per_node to 1 in this case. Print a firmware bug when this is
performed for non-virtualized systems.

  [ bp: Massage commit message. ]