I experimented a lot with Fedora. I tried to install the most actual Distribution, wich is Fedora 17 Beta, togehter with the kernel and Qemu from Rawhide and PAPI via git. Now i understand the problem. Papi_avail detects the events but when i run the examples i nearly always get error -8.
You have written about the problems with overflow. Could it be that the NMI generated by the overflow isn't injected into the VM? If so, the problem would be on the KVM(Kernel) or QEMU side.