I have same issue with xcp-ng running eve-ng (network simulator). eve-ng VM crash when launching qemu with "accel=kvm".
netsted virt and e1000
xe vm-param-get uuid=08c5e1be-f1a6-2179-6d0f-1360f456e6e6 param-name=platform
nic_type: e1000; timeoffset: 1; exp-nested-hvm: true; secureboot: false; videoram: 8; hpet: true; device-model: qemu-upstream-compat; apic: true; device_id: 0001; vga: std; nx: true; pae: true; viridian: false; acpi: 1
eve-ng is built on ubuntu 18.04
root@eve-ng:~# cat /sys/module/kvm_intel/parameters/nested
Y
root@eve-ng:~# uname -a
Linux eve-ng 4.20.17.2-eve-ng-uksm-wg+ #1 SMP Sat Feb 6 11:21:53 UTC 2021 x86_64 x86_64 x86_64 GNU/Linux