109 lines
3.6 KiB
ReStructuredText
109 lines
3.6 KiB
ReStructuredText
|
====================
|
||
|
|
microvm Machine Type
|
||
|
|
====================
|
||
|
|
|
||
|
|
``microvm`` is a machine type inspired by ``Firecracker`` and
|
||
|
|
constructed after its machine model.
|
||
|
|
|
||
|
|
It's a minimalist machine type without ``PCI`` nor ``ACPI`` support,
|
||
|
|
designed for short-lived guests. microvm also establishes a baseline
|
||
|
|
for benchmarking and optimizing both QEMU and guest operating systems,
|
||
|
|
since it is optimized for both boot time and footprint.
|
||
|
|
|
||
|
|
|
||
|
|
Supported devices
|
||
|
|
-----------------
|
||
|
|
|
||
|
|
The microvm machine type supports the following devices:
|
||
|
|
|
||
|
|
- ISA bus
|
||
|
|
- i8259 PIC (optional)
|
||
|
|
- i8254 PIT (optional)
|
||
|
|
- MC146818 RTC (optional)
|
||
|
|
- One ISA serial port (optional)
|
||
|
|
- LAPIC
|
||
|
|
- IOAPIC (with kernel-irqchip=split by default)
|
||
|
|
- kvmclock (if using KVM)
|
||
|
|
- fw_cfg
|
||
|
|
- Up to eight virtio-mmio devices (configured by the user)
|
||
|
|
|
||
|
|
|
||
|
|
Limitations
|
||
|
|
-----------
|
||
|
|
|
||
|
|
Currently, microvm does *not* support the following features:
|
||
|
|
|
||
|
|
- PCI-only devices.
|
||
|
|
- Hotplug of any kind.
|
||
|
|
- Live migration across QEMU versions.
|
||
|
|
|
||
|
|
|
||
|
|
Using the microvm machine type
|
||
|
|
------------------------------
|
||
|
|
|
||
|
|
Machine-specific options
|
||
|
|
~~~~~~~~~~~~~~~~~~~~~~~~
|
||
|
|
|
||
|
|
It supports the following machine-specific options:
|
||
|
|
|
||
|
|
- microvm.x-option-roms=bool (Set off to disable loading option ROMs)
|
||
|
|
- microvm.pit=OnOffAuto (Enable i8254 PIT)
|
||
|
|
- microvm.isa-serial=bool (Set off to disable the instantiation an ISA serial port)
|
||
|
|
- microvm.pic=OnOffAuto (Enable i8259 PIC)
|
||
|
|
- microvm.rtc=OnOffAuto (Enable MC146818 RTC)
|
||
|
|
- microvm.auto-kernel-cmdline=bool (Set off to disable adding virtio-mmio devices to the kernel cmdline)
|
||
|
|
|
||
|
|
|
||
|
|
Boot options
|
||
|
|
~~~~~~~~~~~~
|
||
|
|
|
||
|
|
By default, microvm uses ``qboot`` as its BIOS, to obtain better boot
|
||
|
|
times, but it's also compatible with ``SeaBIOS``.
|
||
|
|
|
||
|
|
As no current FW is able to boot from a block device using
|
||
|
|
``virtio-mmio`` as its transport, a microvm-based VM needs to be run
|
||
|
|
using a host-side kernel and, optionally, an initrd image.
|
||
|
|
|
||
|
|
|
||
|
|
Running a microvm-based VM
|
||
|
|
~~~~~~~~~~~~~~~~~~~~~~~~~~
|
||
|
|
|
||
|
|
By default, microvm aims for maximum compatibility, enabling both
|
||
|
|
legacy and non-legacy devices. In this example, a VM is created
|
||
|
|
without passing any additional machine-specific option, using the
|
||
|
|
legacy ``ISA serial`` device as console::
|
||
|
|
|
||
|
|
$ qemu-system-x86_64 -M microvm \
|
||
|
|
-enable-kvm -cpu host -m 512m -smp 2 \
|
||
|
|
-kernel vmlinux -append "earlyprintk=ttyS0 console=ttyS0 root=/dev/vda" \
|
||
|
|
-nodefaults -no-user-config -nographic \
|
||
|
|
-serial stdio \
|
||
|
|
-drive id=test,file=test.img,format=raw,if=none \
|
||
|
|
-device virtio-blk-device,drive=test \
|
||
|
|
-netdev tap,id=tap0,script=no,downscript=no \
|
||
|
|
-device virtio-net-device,netdev=tap0
|
||
|
|
|
||
|
|
While the example above works, you might be interested in reducing the
|
||
|
|
footprint further by disabling some legacy devices. If you're using
|
||
|
|
``KVM``, you can disable the ``RTC``, making the Guest rely on
|
||
|
|
``kvmclock`` exclusively. Additionally, if your host's CPUs have the
|
||
|
|
``TSC_DEADLINE`` feature, you can also disable both the i8259 PIC and
|
||
|
|
the i8254 PIT (make sure you're also emulating a CPU with such feature
|
||
|
|
in the guest).
|
||
|
|
|
||
|
|
This is an example of a VM with all optional legacy features
|
||
|
|
disabled::
|
||
|
|
|
||
|
|
$ qemu-system-x86_64 \
|
||
|
|
-M microvm,x-option-roms=off,pit=off,pic=off,isa-serial=off,rtc=off \
|
||
|
|
-enable-kvm -cpu host -m 512m -smp 2 \
|
||
|
|
-kernel vmlinux -append "console=hvc0 root=/dev/vda" \
|
||
|
|
-nodefaults -no-user-config -nographic \
|
||
|
|
-chardev stdio,id=virtiocon0 \
|
||
|
|
-device virtio-serial-device \
|
||
|
|
-device virtconsole,chardev=virtiocon0 \
|
||
|
|
-drive id=test,file=test.img,format=raw,if=none \
|
||
|
|
-device virtio-blk-device,drive=test \
|
||
|
|
-netdev tap,id=tap0,script=no,downscript=no \
|
||
|
|
-device virtio-net-device,netdev=tap0
|