hv_passthrough and Windows 11 Performance Issues

[justanopossum]

Hello, I currently have a Windows 11 VM with a GPU passed through and VBS hypervisor enabled. I currently need it enabled because of nested virtualization/game anti-cheat whitelist.

I have some strange performance problems with this setup. When the hv_passthrough flag is enabled. The CPU performance is good, but 3D performance suffers. When hv_passthrough is not enabled, 3D performance is better, but CPU performance suffers.

System Specs:
CPU: Ryzen 7 5800XT
MoBo: AsRock x570 Phantom Gaming S
GPU: GTX 5060TI
Proxmox: 9.1.1

VM Config:

agent: 1
args: -cpu host,hv_passthrough
bios: ovmf
boot: order=scsi0;ide0;net0
cores: 15
cpu: host
efidisk0: local-lvm:vm-100-disk-0,efitype=4m,pre-enrolled-keys=1,size=4M
hostpci0: mapping=rtx5060,pcie=1,x-vga=1
hostpci2: 0000:0a:00.0
ide0: none,media=cdrom
machine: pc-q35-10.0+pve1
memory: 16384
meta: creation-qemu=10.0.2,ctime=1761614335
name: Windows11
net0: virtio=BC:24:11:3E:DE:45,bridge=vmbr0,firewall=1
net1: virtio=BC:24:11:42:76:D7,bridge=iotbr,firewall=1
numa: 0
onboot: 1
ostype: win11
scsi0: local-lvm:vm-100-disk-1,cache=writeback,discard=on,iothread=1,size=500G,ssd=1
scsi1: non_critical:vm-100-disk-0,iothread=1,size=432G
scsihw: virtio-scsi-single
smbios1: uuid=95c65b2f-c130-4c26-8b8c-3b464cb3f54c
sockets: 1
tpmstate0: local-lvm:vm-100-disk-2,size=4M,version=v2.0
usb0: host=1038:1832,usb3=1
usb1: host=445a:1221,usb3=1
usb2: host=1f75:0611,usb3=1
usb3: host=5-1,usb3=1
usb4: host=6-2,usb3=1
vga: none
virtiofs0: bulk-storage,direct-io=1
vmgenid: eb120e53-b556-429e-be31-c7c12117caaa

With hypervisor and hv_passthrough:


With hypervisor and no hv_passthrough:


Without hypervisor:


Is there anything I can do to fix the performance while keeping the windows hypervisor enabled?