How to set up vhost-net in RHEL 6.1?

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RHEL 6.1 release notes mention availability of "new host kernel networking backend - vhost". How can it be configured? I saw some RedHat presentation that suggested that in order to do this one should specify "Linux > Red Hat Enterprise Linux 6.1" in virt-manager; but I can't find this option after updating my system via "yum update".