Virtualization with KVM-QEMU

QEMU is a virtualization solution that is fully open-source and probably the most efficient free option on a Linux kernel. It can use the kernel KVM technology to access the highest possible virtualization level.

The Gentoo Wiki page on QEMU has lots of good information, as well as this page.

I am asusming you use genkernel with gentoo-sources or gentoo-kernel-bin with the dist flags to have a standard kernel, that ships with all the required options enables. If this is not the case, follow the instructions on the Gentoo Wiki page linked above and compile a compliant kernel.

You also need to have all the virtualization options enabled on your BIOS/UEFI firmware.

Now, as for packages, you will want the VirtManager GUI and the QEMU package, so install the following:

emerge app-emulation/libvirt app-emulation/virt-manager qemu -vp

add your users to groups kvm, qemu and libvirt.

gpasswd -a <tuo_utente> libvirt
gpasswd -a <tuo_utente> kvm
rc-update add libvirt-guests
rc-update add libvirtd

/etc/libvirt/libvirtd.conf:

unix_sock_group = "libvirt"
unix_sock_rw_perms = "0770"