Hi Frédéric,
Debug logs are being written to a serial port if you select the "ReactOS
(Debug)" option in the bootloader. It will help to understand what's going on in
the OS. My guess that's some race condition while enumerating devices.
As far as I can see, Xen shares some code with QEMU for device emulation in HVM mode. Thus
this wiki page (
https://reactos.org/wiki/QEMU) may help to tune some settings, because
ReactOS doesn't work with all kinds of modes QEMU offers (namely, q35 chipset
doesn't work,
https://jira.reactos.org/browse/CORE-13346)
Checking latest development build may also help, but we haven't made much changes to
that part of OS recently.
If you will manage to run ReactOS inside Xen, maybe it's worth creating a dedicated
wiki page for that along with other virtualization software.
Anyway, thanks for your interest in our project :)
Victor