This is something we've been working to fix in the community! The good news is that most of the development and testing so far has been on an N36L-based Microserver, where the experimental AMD KVM support seems to work pretty well. There's a github repo -- https://github.com/jclulow/illumos-kvm -- and hopefully I'll get time soon to respin a current SmartOS ISO with the AMD-enabled bits.