Windows 11 Gaming VM with GPU pass-thru

Hardware and the IOMMU dump below were recorded in August 2024. Host software and the domain XML match the same machine as of September 2026.

Property	Value
Date	September 2026
Kernel	6.8.0-139-generic
Distribution	Linux Mint 22.3
QEMU	8.2.2
libvirt	10.0.0

Related: Looking Glass B7 with IVSHMEM, Guest CPU topology vs pin map, CPU governor for pinned KVM vCPUs, Host CPU affinity for pinned VMs, Raw virtio-blk boot disk.

Hardware

Part	Role	Device
Mainboard	Host	ASUS ROG Crosshair VIII Hero
CPU	Host and guest	AMD Ryzen 7 3700X
GPU	Guest (VFIO)	AMD Radeon RX 6900 XT (16 GB)
GPU	Host display	AMD Radeon RX 480 (8 GB)
USB	Guest	VIA VL805/VL806 SuperSpeed USB 3.0 host controller

Two GPUs are required. The host keeps the RX 480. The 6900 XT and its extra functions go to the guest.

Host kernel

Bind the guest GPU functions to vfio-pci and reserve hugepages before QEMU starts. PCI BDFs move if the card changes slot; the IDs do not.

GRUB_CMDLINE_LINUX_DEFAULT="... vfio_pci.ids=1002:73bf,1002:ab28,1002:73a6,1002:73a4 kvm.ignore_msrs=1 hugepages=8192"

8192 pages of 2 MiB is 16 GiB. Confirm page size with grep Hugepagesize /proc/meminfo.

/etc/sysctl.conf:

kernel.shmmax = 17179869184
vm.nr_hugepages = 8192
vm.min_free_kbytes = 112640
vm.hugetlb_shm_group = 1000

hugetlb_shm_group is the desktop user’s gid so QEMU can use the pool.

Guest GPU (VFIO)

Navi 21 exposes four functions. Pass all of them. In the 2024 dump they sat at 0b:00.0–0b:00.3 (IOMMU groups 26–29):

0b:00.0 VGA compatible controller [1002:73bf]  Navi 21 (RX 6900 XT)
0b:00.1 Audio device             [1002:ab28]  HDMI audio
0b:00.2 USB controller           [1002:73a6]
0b:00.3 Serial bus controller    [1002:73a4]  Navi 21 USB

The full group list is in IOMMU dump.

USB passthrough

A dedicated USB controller goes to the guest so keyboard, mouse, and similar devices do not share the host xHCI. On this board the front-panel Matisse controller (1022:149c at 06:00.3) holds the G815 and a Cherry keyboard.

lsusb before that controller is unbound (host still sees those devices):

Bus 003 Device 003: ID 046a:0001 Cherry GmbH Keyboard
Bus 003 Device 009: ID 046d:c33f Logitech, Inc. G815 Mechanical Keyboard

After bind, those buses disappear from the host. Remaining host USB is the rear hub (AURA, headset dongle, Bluetooth, webcam, and the Cooler Master ARES on the 6900 XT’s own USB).

Domain CPU and memory

Pin the guest to host CPUs 8-15. Leave 0-7 for the desktop. Those eight host CPUs are not four SMT pairs, so the guest topology is 8 cores / 1 thread. cores=4 threads=2 does not match this pin map. See Guest CPU topology vs pin map.

A SATA qcow2 system disk should be converted to raw virtio-blk once viostor is a Boot-start driver. Recipe: Raw virtio-blk boot disk.

<vcpu placement="static" cpuset="8-15">8</vcpu>
<iothreads>2</iothreads>
<cputune>
  <vcpupin vcpu="0" cpuset="8"/>
  <vcpupin vcpu="1" cpuset="9"/>
  <vcpupin vcpu="2" cpuset="10"/>
  <vcpupin vcpu="3" cpuset="11"/>
  <vcpupin vcpu="4" cpuset="12"/>
  <vcpupin vcpu="5" cpuset="13"/>
  <vcpupin vcpu="6" cpuset="14"/>
  <vcpupin vcpu="7" cpuset="15"/>
  <emulatorpin cpuset="0-1"/>
  <iothreadpin iothread="1" cpuset="0-1"/>
  <iothreadpin iothread="2" cpuset="2-3"/>
</cputune>

<cpu mode="host-passthrough" check="none" migratable="on">
  <topology sockets="1" dies="1" cores="8" threads="1"/>
  <cache mode="passthrough"/>
  <feature policy="require" name="topoext"/>
</cpu>

<memoryBacking>
  <hugepages>
    <page size="2048" unit="KiB"/>
  </hugepages>
  <access mode="shared"/>
</memoryBacking>

access mode=shared is required for virtiofs. On Mint 22, rust virtiofsd 1.10 cannot share a domain with /dev/kvmfr0 (Illegal seek). Looking Glass on a virtiofs guest must use /dev/shm — see Looking Glass B7.

Spice stays for input. Do not add a QXL head when the 6900 XT is the only display.

Host CPU tuning

Keep host CPUs 8-15 on performance so pinned vCPUs can clock up. A udev rule on ACTION=="add" is the first step:

echo 'KERNEL=="cpu8|cpu9|cpu10|cpu11|cpu12|cpu13|cpu14|cpu15", SUBSYSTEM=="cpu", ACTION=="add", ATTR{cpufreq/scaling_governor}="performance"' | sudo tee /etc/udev/rules.d/90-scaling-governor-performance.rules

After a Debian / Mint upgrade, cpufrequtils may start later and write ondemand to every CPU. Confirm with cat /sys/devices/system/cpu/cpu*/cpufreq/scaling_governor. If everything is ondemand, the udev rule lost the race. Restore performance on the pinned CPUs with the oneshot in CPU governor for pinned KVM vCPUs.

Keep host IRQs off the guest CPUs:

# /etc/default/irqbalance
IRQBALANCE_BANNED_CPULIST=8-15

sudo systemctl restart irqbalance

isolcpus=8-15 was tried and not proven better. Leave it off unless you re-test host and guest together. Prefer systemd slice AllowedCPUs= so host userspace stays off the guest CPUs without a kernel cmdline change: Host CPU affinity for pinned VMs.

Bridge

One way to put the guest on the LAN is a oneshot that builds br0 on the I211 (enp5s0):

# /lib/systemd/system/qemu-startup.service
[Unit]
Description=Setup qemu network bridging
After=network-online.target

[Service]
Type=oneshot
Restart=on-failure
ExecStart=brctl addbr br0
ExecStart=brctl addif br0 enp5s0
ExecStart=dhclient br0
ExecStart=ip link set br0 up
ExecStart=iptables -I FORWARD -m physdev --physdev-is-bridged -j ACCEPT

[Install]
WantedBy=multi-user.target

sudo systemctl enable --now qemu-startup.service

The guest NIC is virtio on that bridge.

Resources

• Sharing files with virtiofs
• Virtiofs on Windows
• WinFsp
• Static hugepages for VMs
• KVM hugepages (Ubuntu)
• Performance tweaks for KVM/QEMU GPU passthrough
• Windows guest performance on QEMU
• CPU governor via udev
• Bridged networking with libvirt
• Simple QEMU bridging
• IOMMU group script: https://gist.github.com/r15ch13/ba2d738985fce8990a4e9f32d07c6ada

IOMMU dump

August 2024. [R] means the group has a reset. USB lines are devices on that controller at capture time.

Group 0:    [1022:1482]     00:01.0  Host bridge                              Starship/Matisse PCIe Dummy Host Bridge
Group 1:    [1022:1483] [R] 00:01.1  PCI bridge                               Starship/Matisse GPP Bridge
Group 2:    [1022:1483] [R] 00:01.2  PCI bridge                               Starship/Matisse GPP Bridge
Group 3:    [1022:1482]     00:02.0  Host bridge                              Starship/Matisse PCIe Dummy Host Bridge
Group 4:    [1022:1482]     00:03.0  Host bridge                              Starship/Matisse PCIe Dummy Host Bridge
Group 5:    [1022:1483] [R] 00:03.1  PCI bridge                               Starship/Matisse GPP Bridge
Group 6:    [1022:1483] [R] 00:03.2  PCI bridge                               Starship/Matisse GPP Bridge
Group 7:    [1022:1482]     00:04.0  Host bridge                              Starship/Matisse PCIe Dummy Host Bridge
Group 8:    [1022:1482]     00:05.0  Host bridge                              Starship/Matisse PCIe Dummy Host Bridge
Group 9:    [1022:1482]     00:07.0  Host bridge                              Starship/Matisse PCIe Dummy Host Bridge
Group 10:   [1022:1484] [R] 00:07.1  PCI bridge                               Starship/Matisse Internal PCIe GPP Bridge 0 to bus[E:B]
Group 11:   [1022:1482]     00:08.0  Host bridge                              Starship/Matisse PCIe Dummy Host Bridge
Group 12:   [1022:1484] [R] 00:08.1  PCI bridge                               Starship/Matisse Internal PCIe GPP Bridge 0 to bus[E:B]
Group 13:   [1022:790b]     00:14.0  SMBus                                    FCH SMBus Controller
        [1022:790e]     00:14.3  ISA bridge                               FCH LPC Bridge
Group 14:   [1022:1440]     00:18.0  Host bridge                              Matisse/Vermeer Data Fabric: Device 18h; Function 0
        [1022:1441]     00:18.1  Host bridge                              Matisse/Vermeer Data Fabric: Device 18h; Function 1
        [1022:1442]     00:18.2  Host bridge                              Matisse/Vermeer Data Fabric: Device 18h; Function 2
        [1022:1443]     00:18.3  Host bridge                              Matisse/Vermeer Data Fabric: Device 18h; Function 3
        [1022:1444]     00:18.4  Host bridge                              Matisse/Vermeer Data Fabric: Device 18h; Function 4
        [1022:1445]     00:18.5  Host bridge                              Matisse/Vermeer Data Fabric: Device 18h; Function 5
        [1022:1446]     00:18.6  Host bridge                              Matisse/Vermeer Data Fabric: Device 18h; Function 6
        [1022:1447]     00:18.7  Host bridge                              Matisse/Vermeer Data Fabric: Device 18h; Function 7
Group 15:   [15b7:5030] [R] 01:00.0  Non-Volatile memory controller           Device 5030
Group 16:   [1022:57ad] [R] 02:00.0  PCI bridge                               Matisse Switch Upstream
Group 17:   [1022:57a3] [R] 03:01.0  PCI bridge                               Matisse PCIe GPP Bridge
Group 18:   [1022:57a3] [R] 03:05.0  PCI bridge                               Matisse PCIe GPP Bridge
Group 19:   [1022:57a4] [R] 03:08.0  PCI bridge                               Matisse PCIe GPP Bridge
        [1022:1485] [R] 06:00.0  Non-Essential Instrumentation [1300]     Starship/Matisse Reserved SPP
        [1022:149c]     06:00.1  USB controller                           Matisse USB 3.0 Host Controller
Group 20:   [1022:57a4] [R] 03:09.0  PCI bridge                               Matisse PCIe GPP Bridge
        [1022:7901] [R] 07:00.0  SATA controller                          FCH SATA Controller [AHCI mode]
Group 21:   [1022:57a4] [R] 03:0a.0  PCI bridge                               Matisse PCIe GPP Bridge
        [1022:7901] [R] 08:00.0  SATA controller                          FCH SATA Controller [AHCI mode]
Group 22:   [15b7:5002] [R] 04:00.0  Non-Volatile memory controller           WD Black 2018/SN750 / PC SN720 NVMe SSD
Group 23:   [8086:1539] [R] 05:00.0  Ethernet controller                      I211 Gigabit Network Connection
Group 24:   [1002:1478] [R] 09:00.0  PCI bridge                               Navi 10 XL Upstream Port of PCI Express Switch
Group 25:   [1002:1479] [R] 0a:00.0  PCI bridge                               Navi 10 XL Downstream Port of PCI Express Switch
Group 26:   [1002:73bf] [R] 0b:00.0  VGA compatible controller                Navi 21 [Radeon RX 6800/6800 XT / 6900 XT]
Group 27:   [1002:ab28]     0b:00.1  Audio device                             Navi 21 HDMI Audio [Radeon RX 6800/6800 XT / 6900 XT]
Group 28:   [1002:73a6]     0b:00.2  USB controller                           Device 73a6
Group 29:   [1002:73a4]     0b:00.3  Serial bus controller                    Navi 21 USB
Group 30:   [1002:67df] [R] 0c:00.0  VGA compatible controller                Ellesmere [Radeon RX 470/480/570/570X/580/580X/590]
        [1002:aaf0]     0c:00.1  Audio device                             Ellesmere HDMI Audio [Radeon RX 470/480 / 570/580/590]
Group 31:   [1022:148a] [R] 0d:00.0  Non-Essential Instrumentation [1300]     Starship/Matisse PCIe Dummy Function
Group 32:   [1022:1485] [R] 0e:00.0  Non-Essential Instrumentation [1300]     Starship/Matisse Reserved SPP
Group 33:   [1022:1486] [R] 0e:00.1  Encryption controller                    Starship/Matisse Cryptographic Coprocessor PSPCPP
Group 34:   [1022:149c] [R] 0e:00.3  USB controller                           Matisse USB 3.0 Host Controller
Group 35:   [1022:1487]     0e:00.4  Audio device                             Starship/Matisse HD Audio Controller