Android Studio: /dev/kvm device permission denied

As mentioned in the comments, starting with Ubuntu 18.04 and Linux Mint Tara you need to first sudo apt install qemu-kvm.

To check the ownership of /dev/kvm use

ls -al /dev/kvm

The user was root, the group kvm. To check which users are in the kvm group, use

grep kvm /etc/group

This returned

kvm:x:some_number:

on my system: as there is nothing rightwards of the final :, there are no users in the kvm group.

To add your user to the kvm group, you could use

sudo adduser $USER kvm

which adds the user to the group, and check once again with grep kvm /etc/group.

As mentioned by @Knossos, you might want to log out and back in (or restart), for the permissions to take effect.