Are you getting this error when trying to start a libvirt KVM VM on Fedora 20?

qemu-system-x86_64: error while loading shared libraries: failed to map segment from shared object: Permission denied

Seems to be caused by Nvidia proprietary drivers. Whatever black magic they are doing behind the scenes is upsetting the selinux restrictions qemu is run under.

The fix: sudo setsebool -P virt_use_execmem=on

(update Jan 2016: the original bug that prompted this post had some follow up discussion about a possible cause, so maybe it's fixable: