@AndreS I mentionned it already but I can repeat again. My system is already installed in 3 partitions: /boot, /boot/efi and the last one is encrypted, inside 2 LVM volumes, one for swap and and the other one as root.

I can't try just xen without LVM and dmcrypt, because my system is already installed.

And no, I am not trying to add 3 in one, without Xen, my system work already with LVM and dmcrypt