This drivers provides support for virtio based paravirtual device drivers over PCI. This requires that your VMM has appropriate PCI virtio backends. Most QEMU based VMMs should support these devices (like KVM or Xen). Currently, the ABI is not considered stable so there is no guarantee that this version of the driver will work with your VMM. If unsure, say M.
This driver supports increasing and decreasing the amount of memory within a KVM guest. If unsure, say M.