By default Gnome Boxes use qemu:///session instead of qemu:///system because make desktop integration easier avoiding permission issues.
But if I what to share the same VM on the same desktop with another user (my wife), “qemu:///session” and “SELinux” can be an issue. On Fedora sVirt and SELinux is enabled by default. This make impossible to run the same VM from different user (not at the same time) due to Dynamic Resource Labeling.
The easiest solution I’ve found was to disable SELinux only for the domain “virt_t”.
First export your VM settings (if you already have a VM):
virsh dumpxml sharedVM > sharedVM.xml
Then move the VM image to a folder that both users can access (and write). In my case:
Set the owner and permission to the new VM folders:
chown root:users /home/Public/VMs
chmod 777 /home/Public/VMs
..and update sharedVM.xml according to the new path.
Import the exported VM on both users. Run this command for both account:
virsh create sharedVM.xml
Set Virt Domain in Permissive mode:
semanage permissive -a virt_t
Now you can start sharedVM with either one of the two users.