My configuration /etc/pve/qemu-server/200.conf:
args: -global qxl-vga.ram_size=268435456 -global qxl-vga.vram_size=268435456 -global qxl-vga.vgamem_mb=64
https://pve.proxmox.com/pipermail/pve-user/2017-July/168622.html
http://linux-blog.anracom.com/2017/07/06/kvmqemu-mit-qxl-hohe-aufloesungen-und-virtuelle-monitore-im-gastsystem-definieren-und-nutzen-i/
