On trying to fire up a VM using virt-manager, I get "unable to map backing store for guest RAM: Permission denied".
I use hugepages to lock down memory for the VM, which may be relevant for the error. This worked correctly on F26 just before the upgrade to F27. I have changed nothing in my VM configuration, nor in the config file for QEMU. However, temporarily turning off SElinux allows the startup to proceed, after which I can re-enable SElinux with no ill effects, i.e. the VM runs correctly.
A complete relabel of my system (touch /.autolabel and reboot) has made no difference.