Currently if qemu is started as user it can't use vhost_net accelerator since ownership and perms on /dev/vhost-net are left as root:root 0600, which results in "tap: open vhost char device failed: Permission denied" error when starting qemu. Simplest fix is to make udev rules for /dev/kvm also cover /dev/vhost-net like, for example, Arch does: https://git.archlinux.org/svntogit/packages.git/tree/trunk/65-kvm.rules?h=packages/qemu Note this is a separate issue from tun/tap perms which can be set at network interface creation time.
commit acc843fe087a30413d5603826d659826a3b599ae Author: Matthias Maier <tamiko@gentoo.org> Date: Mon Feb 13 00:21:02 2017 -0600 app-emulation/qemu: fix permissions on vhost-net, bug #593196 Add an additional udev rule that grants access to /dev/vhost-net to the kvm user. Package-Manager: Portage-2.3.3, Repoman-2.3.1