Hello, We found that the OVMF build used in Debian (with Xen using bios="ovmf") fails to boot a nested Xen due to problematic ACPI tables, along other issues like 1 vCPU Linux guests and very slow boot. It looks like Debian uses a build of OVMF that doesn't have Xen support, which appears to cause the ACPI tables to get bogus, among some other issues. In OVMF source code, there is a separate OvmfXen.dsc which has Xen-specific drivers (PV drivers) and logic that probably needs to be built separately and be used for Xen instead. Teddy