Xubuntu 16.04 L0 hypervisor kernel panics L1 CentOS 7.5.1804 guest

OK, so the title needs a little explanation:)

I have Xubuntu 16.04.5 LTS installed in my workstation. In there I have installed virt-manager, libvirt, qemu etc. to run a CentOS 7.5 VM as another hypervisor using nested virtualization; this VM works.

What does not work however is inside of the CentOS VM installing virt-manager, libvirt, qemu, etc. and run another VM inside of that. Trying to start a CentOS VM inside my L1 CentOS hypervisor kernel panics very soon after grub with a backtrace like this:

[ 1.441389] general protection fault: 0000 [#1] SMP
[ 1.442030] Modules linked in:
[ 1.442030] CPU: 0 PID: 47 Comm: kworker/u2:1 Not tainted 3.10.0-862.el7.x86_64 #1
[ 1.442030] Hardware name: Red Hat KVM, BIOS 0.5.1 01/01/2011
[ 1.442030] task: ffff8b1d3868dee0 ti: ffff8b1d3f8fc000 task.ti: ffff8b1d3f8fc000
[ 1.442030] RIP: 0010:[<ffffffffa6a22ce5>] [<ffffffffa6a22ce5>] flush_old_exec+0x725/0x980
[ 1.442030] RSP: 0018:ffff8b1d3f8ffd00 EFLAGS: 00010246
[ 1.442030] RAX: 0000000000000001 RBX: 0000000000000000 RCX: 0000000000000049
[ 1.442030] RDX: 0000000000000000 RSI: ffff8b1d3f8dc640 RDI: ffff8b1d3f8dc000
[ 1.442030] RBP: ffff8b1d3f8ffd60 R08: 0000000000000046 R09: 0000000000000000
[ 1.442030] R10: 000000002b764c0c R11: ffffbfc001fe3000 R12: ffff8b1d3f8dc640
[ 1.442030] R13: ffff8b1d3f8dc000 R14: ffff8b1d3868dee0 R15: ffff8b1d37e4c100
[ 1.442030] FS: 0000000000000000(0000) GS:ffff8b1d3bc00000(0000) knlGS:0000000000000000
[ 1.442030] CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
[ 1.442030] CR2: 00007fc3814202a8 CR3: 0000000061c0e000 CR4: 00000000003606f0
[ 1.442030] DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
[ 1.442030] DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
[ 1.442030] Call Trace:
[ 1.442030] [<ffffffffa6a7e44c>] load_elf_binary+0x33c/0xe50
[ 1.442030] [<ffffffffa6af34d9>] ? ima_bprm_check+0x49/0x50
[ 1.442030] [<ffffffffa6a7e110>] ? load_elf_library+0x220/0x220
[ 1.442030] [<ffffffffa6a2202f>] search_binary_handler+0xef/0x310
[ 1.442030] [<ffffffffa6a2380b>] do_execve_common.isra.24+0x5db/0x6e0
[ 1.442030] [<ffffffffa6a23928>] do_execve+0x18/0x20
[ 1.442030] [<ffffffffa68af8ef>] ____call_usermodehelper+0xff/0x140
[ 1.442030] [<ffffffffa68af7f0>] ? call_usermodehelper+0x60/0x60
[ 1.442030] [<ffffffffa6f1f637>] ret_from_fork_nospec_begin+0x21/0x21
[ 1.442030] [<ffffffffa68af7f0>] ? call_usermodehelper+0x60/0x60
[ 1.442030] Code: cf e9 ff 4c 89 f7 e8 fb 32 e7 ff e9 4d fa ff ff 65 8b 05 37 a3 5e 59 a8 01 0f 84 85 fc ff ff 31 d2 b8 01 00 00 00 b9 49 00 00 00 <0f> 30 0f 1f 44 00 00 48 c7 c0 10 00 00 00 e8 07 00 00 00 f3 90
[ 1.442030] RIP [<ffffffffa6a22ce5>] flush_old_exec+0x725/0x980
[ 1.442030] RSP <ffff8b1d3f8ffd00>
[ 1.669827] ---[ end trace acc22b186f1c20ae ]---
[ 1.674444] Kernel panic - not syncing: Fatal exception
[ 1.675410] Kernel Offset: 0x25800000 from 0xffffffff81000000 (relocation range: 0xffffffff80000000-0xffffffffbfffffff)

However, using the exact same procedure is successfull using an Xubuntu 18.04 as L0 instead!

So, to simplify:

Xubuntu 16.04 -> CentOS 7.5.1804 -> CentOS 7.5.1804 = Kernel panic

Xubuntu 18.04 -> CentOS 7.5.1804 -> CentOS 7.5.1804 = Success!

Please know if there´s any more information you need!

Thanks in advance!
/K
---
ApportVersion: 2.20.1-0ubuntu2.18
Architecture: amd64
AudioDevicesInUse:
 USER PID ACCESS COMMAND
 /dev/snd/controlC1: karli 2591 F.... pulseaudio
 /dev/snd/controlC0: karli 2591 F.... pulseaudio
CurrentDesktop: XFCE
DistroRelease: Ubuntu 16.04
HibernationDevice: RESUME=/dev/mapper/vg00-swap_1
Lsusb:
 Bus 002 Device 001: ID 1d6b:0003 Linux Foundation 3.0 root hub
 Bus 001 Device 003: ID 138a:0090 Validity Sensors, Inc.
 Bus 001 Device 002: ID 04f2:b52c Chicony Electronics Co., Ltd
 Bus 001 Device 004: ID 8087:0a2b Intel Corp.
 Bus 001 Device 001: ID 1d6b:0002 Linux Foundation 2.0 root hub
MachineType: LENOVO 20EN0013US
NonfreeKernelModules: nvidia_uvm nvidia_drm nvidia_modeset nvidia
Package: linux (not installed)
ProcFB: 0 VESA VGA
ProcKernelCmdLine: BOOT_IMAGE=/vmlinuz-4.4.0-131-generic root=/dev/mapper/vg00-root ro quiet splash vt.handoff=7
ProcVersionSignature: Ubuntu 4.4.0-131.157-generic 4.4.134
RelatedPackageVersions:
 linux-restricted-modules-4.4.0-131-generic N/A
 linux-backports-modules-4.4.0-131-generic N/A
 linux-firmware 1.157.20
Tags: xenial
Uname: Linux 4.4.0-131-generic x86_64
UpgradeStatus: No upgrade log present (probably fresh install)
UserGroups: adm cdrom dialout dip fax floppy games libvirtd lpadmin plugdev sambashare sudo tape video
_MarkForUpload: True
dmi.bios.date: 09/28/2017
dmi.bios.vendor: LENOVO
dmi.bios.version: N1EET73W (1.46 )
dmi.board.asset.tag: Not Available
dmi.board.name: 20EN0013US
dmi.board.vendor: LENOVO
dmi.board.version: 0B98417 PRO
dmi.chassis.asset.tag: No Asset Information
dmi.chassis.type: 10
dmi.chassis.vendor: LENOVO
dmi.chassis.version: None
dmi.modalias: dmi:bvnLENOVO:bvrN1EET73W(1.46):bd09/28/2017:svnLENOVO:pn20EN0013US:pvrThinkpadP50:rvnLENOVO:rn20EN0013US:rvr0B98417PRO:cvnLENOVO:ct10:cvrNone:
dmi.product.name: 20EN0013US
dmi.product.version: Thinkpad P50
dmi.sys.vendor: LENOVO