Hiding CPUID from AppVM (why is this not default)?

[deeplow]

(Adjusted your title for clarity, but fell free to tweak it if it is not adequate)

I think this will answer your question (marmarek is the lead developer of Qubes):

Windows 10 libvirt config syntax help to hide hypervisor info

Xen does not support changing this part of CPUID out of the box. Whatever you set in libvirt, Xen will always announce itself in CPUID 0x40xxxxxx leafs. Some people attempt patch Xen for that: Spoofing CPUID Results in the Linux-Stubdom Crashing · Issue #4980 · QubesOS/qubes-issues · GitHub, but as you can see, it isn’t fully successful.