QEMU

QEMU

QEMU supports a number of hypervisors (known as accelerators) as well as a JIT known as the Tiny Code Generator (TCG) capable of emulating many CPUs.

Accelerator	Host OS	Host Architectures
KVM	Linux	Arm (64 bit only), MIPS, PPC, RISC-V, s390x, x86
Xen	Linux (as dom0)	Arm, x86
Hypervisor Framework (hvf)	MacOS	x86 (64 bit only), Arm (64 bit only)
Windows Hypervisor Platform (whpx)	Windows	x86
NetBSD Virtual Machine Monitor (nvmm)	NetBSD	x86
Tiny Code Generator (tcg)	Linux, other POSIX, Windows, MacOS	Arm, x86, Loongarch64, MIPS, PPC, s390x, Sparc64

QEMU Options

Options	Description
Machine	Define the machine type, amount of memory etc
CPU	Type and number/topology of vCPUs. Most accelerators offer a host cpu option which simply passes through your host CPU configuration without filtering out any features.
Accelerator	This will depend on the hypervisor you run. Note that the default is TCG, which is purely emulated, so you must specify an accelerator type to take advantage of hardware virtualization.
Devices	Additional devices that are not defined by default with the machine type.
Backends	Backends are how QEMU deals with the guest’s data, for example how a block device is stored, how network devices see the network or how a serial device is directed to the outside world.
Interfaces	How the system is displayed, how it is managed and controlled or debugged.
Boot	How the system boots, via firmware or direct kernel boot.

$ qemu-system-aarch64 \
   -machine type=virt,virtualization=on,pflash0=rom,pflash1=efivars \
   -m 4096 \
   -cpu max,pauth-impdef=on \
   -smp 4 \
   -accel tcg \
   -device virtio-net-pci,netdev=unet \
   -device virtio-scsi-pci \
   -device scsi-hd,drive=hd \
   -netdev user,id=unet,hostfwd=tcp::2222-:22 \
   -blockdev driver=raw,node-name=hd,file.driver=host_device,file.filename=/dev/lvm-disk/debian-bullseye-arm64 \
   -blockdev node-name=rom,driver=file,filename=(pwd)/pc-bios/edk2-aarch64-code.fd,read-only=true \
   -blockdev node-name=efivars,driver=file,filename=$HOME/images/qemu-arm64-efivars
   -serial mon:stdio \
   -display none \

Device Emulation

Device Front End

All devices can be specified with the --device command line option.

A front end is often paired with a back end, which describes how the host’s resources are used in the emulation.

Device Buses

• In most cases the BUS a device is attached to can be inferred, for example PCI devices are generally automatically allocated to the next free address of first PCI bus found.

• In complicated configurations you can explicitly specify what bus (bus=ID) a device is attached to along with its address (addr=N).

Some devices, for example a PCI SCSI host controller, will add an additional buses to the system that other devices can be attached to.

–device foo,bus=pci.0,addr=0,id=foo 
–device bar,bus=foo.0,addr=1,id=baz

which would be a bar device (with the ID of baz) which is attached to the first foo bus (foo.0) at address 1. The foo device which provides that bus is itself is attached to the first PCI bus (pci.0).

Device Back End

The back end describes how the data from the emulated device will be processed by QEMU.

1. Serial devices will be backed by a --chardev which can redirect the data to a file or socket or some other system.

2. Storage devices are handled by --blockdev which will specify how blocks are handled, for example being stored in a qcow2 file or accessing a raw host disk partition.

Device Pass Through

• Exposing a single USB device on the host system to the guest.

• Dedicating a video card in a PCI slot to the exclusive use of the guest.