File kvm-supported.txt of Package qemu
SLES 12 SP1 QEMU/KVM RELATED SUPPORT STATEMENTS
The QEMU packages included with SLES 12 SP1 provide a large variety of
features, from the very latest customer requests to features of questionable
quality or value. This document was created to assist the user in deciding
which features can be relied upon to build enterprise class virtualization
solutions. KVM virtualization for the System z host (s390x) is provided as a
technology preview while on x86 support is offered at the L3 (full support)
KVM is implemented as linux kernel modules, which enables the linux kernel to
function as an integral part of the KVM hypervisor. The hypervisor-guest
interaction is controlled by QEMU through the /dev/kvm ioctl interface. The
linux host assists in the virtualization of storage, networking and display
resources as well as direct hardware passthrough of PCI and USB devices. Linux
memory and cpu management features are used by both KVM and QEMU to enable
guests to share host resources as efficiently as possible.
QEMU is a primary component of KVM based virtualization. The legacy qemu-kvm
program is provided for continuity with pre SLES 12 usage, including in
libvirt xml references. The QEMU emulator binaries qemu-system-x86_64 and
qemu-system-i386 (x86 host) and qemu-system-s390x (System z host) are now the
primary programs to use to enable KVM virtualization. When using these
programs, the -machine option accel=kvm (or its alias -enable-kvm) must be
specified for KVM accelation to be active.
Libvirt is the preferred means of accessing QEMU/KVM functionality. This
document focuses on the features and direct usage of QEMU/KVM. Refer to other
documentation for libvirt and libvirt based tools usage.
Major QEMU/KVM Supported Features
- KVM virtualization is accomplished by using the QEMU program in KVM
acceleration mode. KVM acceleration requires that both guest and host have
the same fundamental architecture.
- Guest images created under previous QEMU versions are supported through
machine types which match up with these previous versions.
- For ease of use, the QEMU program has defaults which represent traditional
- Guest virtual machine characteristics are specified by a combination of
internal defaults, given on the QEMU program command-line, and optional config
files. Run-time control is done through either through the Human Monitor
"Protocol" (HMP), or the JSON based programmatical QEMU Monitor Protocol
(QMP) interface. Since a KVM guest runs in the context of a normal linux
process, some types of execution controls are managed with normal linux tools.
- Various standard vCPU types are available, along with the ability to specify
specific CPU features visible to the guest.
- QEMU incorporates a SEABIOS based system BIOS and iPXE based PXE ROMs which
allow boot options common to PC's along with other features tailored to
virtualization. Various VGABIOS ROMs (also from the SEABIOS project) are also
- Some QEMU messages have been localized to various languages. This is provided
by the qemu-lang package. Keyboard mappings for various nationalities is also
- Virtual machine lifecycle controls include startup through the system bios or
using kernel boot, ACPI or legacy based shutdown, execution pausing, and the
saving and restoring of machine state. Two varieties of "monitors" are
provided for controlling runtime aspects of the VM: the human monitor, and a
JSON based QMP (See /usr/share/doc/packages/kvm/qmp-commands.txt).
- Guest execution state may be "moved" in both time (save/restore) and space
(static and live migration). Guest migration from SLES 12 GA to SLES 12 SP1
hosts is supported.
- Security considerations include secccomp2 based sandboxing, vTPM, privileged
helpers and security models for executing QEMU as non-root users.
- QEMU is able to run a wide range of common operating systems as guests. See
the online SUSE documentation for supported OS's. Windows guests can
optionally be accelerated with QEMU/KVM provided Hyper-V hypercalls, or with
paravirtual drivers from the SUSE Virtual Machine Driver Pack.
- QEMU provides best effort reuse of existing disk images, including those with
systems installed, through geometry probing. Also disk images produced by
other popular virtualization technologies may be imported into QEMU supported
storage formats. These QEMU formats include features which exploit the
benefits of virtualization.
- Memory, cpu and disk space overcommit are possible and can be beneficial when
done responsibly. Additional management of these resources comes in the form
of memory ballooning, Host KSM, vcpu hot-add, online disk resizing, trim,
discard and hole punching.
- Guest performance is enhanced through the use of virtio devices, various disk
caching modes, network acceleration via the vhost-net kernel module including
zero copy optimizations, multiqueue network transmit capabilities, host
transparent huge pages (THP) and direct hugetlb usage. Physical PCI and USB
devices may also be passed through to the guest, including SR-IOV VF's.
- The guest's UI is accessable via GTK, SDL, VNC, Spice, and serial (including
curses TUI) interfaces.
- Guest timekeeping is supported in a variety of ways, including a paravirtual
clocksource, and options for the various guest clocks for how to handle the
timeslicing of the guest's execution on the host.
- Guest OS's interact with virtualized hardware including a choice of either
older or more recent x86 system chipsets, system devices and buses, and a
variety of common storage and networking emulated devices. SMBIOS and ACPI
table details can be customized. Virtio based para-virtual devices are
available for more efficient I/O.
- In addition to the para-virtualized devices already mentioned, other devices
and infrastructure designed to avoid virtualization "problem areas" are
available such as SPICE graphics, vmmouse emulation and tablet style pointer
- A built-in user-mode network (SLIRP) stack is available.
- Portions of the host file system may be shared with a guest by using virtFS.
- A guest "agent" is available for SLES 12 SP1 KVM guests (see qemu-guest-agent
package). This allows some introspection and control of the guest OS
environment from the host.
- The following features were previously in a technology preview status, but are
now fully supported:
- virtio-blk-dataplane has now been fully integrated with the block subsystem.
- RADOS Block Devices (RBD)
QEMU/KVM Technology Previews
- KVM on System z using the qemu-system-s390x system emulator is not yet fully
supported. Other support statements made throughout this document generally
refer to x86 usage only.
- Specifying and placing PCI devices on a PCI bridge allows for a greater number
- Nested VMX and SVM virtualization is possible.
- virtio-blk-data-plane allows higher block I/O rates
Noteworthy QEMU/KVM Unsupported Features
- Note that some features are unsupported simply due to lack of validation. If
an existing feature is desired, but not marked supported, let SUSE know about
- The TCG "acceleration" mode may be helpful for problem isolation, but
otherwise presents insufficient benefit and stability.
- Use of -cpu host is not supported in all host/guest configurations.
- ISCSI integration is not enabled in QEMU. It is however possible for guests to
access iSCSI targets available to the host via the blockio interfaces.
- GlusterFS integration is not enabled.
Deprecated, Superseded, Modified and Dropped Features
- When no video adapter is specified, the default used is stdvga. This differs
from the default of prior releases which was cirrus. The cirrus adapter was
considered too outdated to continue to use as the default.
- The deprecated windows drivers (win-virtio-drivers.iso) are no longer provided.
The Virtual Machine Driver Pack is the supported way to get virtio drivers for
- The use of ",boot=on" for virtio disks is no longer needed since the bios used
supports the virtio block interface directly. In fact, its usage may cause
problems, and is now considered deprecated.
- The use of "?" as a parameter to "-cpu", "-soundhw", "-device", "-M",
"-machine", "-d", and "-clock" is now considered deprecated. Use "help"
- Passthrough of a host floppy device is now considered deprecated.
- Use of aio=native without direct cache mode also being specified is now
considered deprecated. (It has no effect in this case).
- The use of image encryption in qcow and qcow2 formats is now considered deprecated.
Analysis has shown it to be weak encryption, in addition to suffering from poor
design. Images can easily be converted to a non-encrypted format.
- Use of acpi, boot-opts, and smp-opts in a -readconfig config file are now
considered deprecated. In the future those names will be standardized to
acpitable, boot, and smp respectively.
- When only a partial SMP topology is provided (ie only some of sockets, cores,
threads) the derived guest ABI is not guaranteed to be equivalent in future
- These previously supported command line options are no longer recognized:
-device pc-sysfw (no longer needed)
- The previously supported blkdev-add QMP command has been flagged as lacking
and could possibly change syntax in the future.
- These previously unsupported command line options are now deprecated:
-no-kvm-irqchip (use -machine kernel_irqchip=off instead)
- The case of specified sockets, cores, and threads not matching the vcpu count
is no longer silently ignored. QEMU now requires that the topology to match up
with the vcpu count.
- These previously unsupported command line options are no longer recognized:
-device testdev (use -device pc-testdev instead)
-kvm-shadow-memory (use -machine kvm_shadow_mem= instead)
-pcidevice (use -device pci-assign instead)
- These previously supported monitor commands are no longer recognized:
pci_add (use device_add instead)
pci_del (use device_del instead)
- These previously unsupported monitor commands are no longer recognized:
QEMU Command-Line and Monitor Syntax and Support
- The QEMU program command-line syntax is as follows:
qemu-system-i386 [options] [disk_image]
qemu-system-x86_64 [options] [disk_image]
Where 'options' are taken from the options listed below, and 'disk_image' is
the file system reference to the the x86 guest's primary IDE based hard disk
image. This image as well as those used with -drive or -cdrom, may be in the
raw (no format), qcow2 or qed storage formats, and may be located in files
within the host filesystem, logical volumes, host physical disks, or network
based storage. Read only media may also be accessed via URL style protocol
- The following command line options are supported:
-cpu ... (all except host)
(the following are aliases of these supported devices: ahci|
-drive ... (if specified if=[ide|floppy|virtio] and format=[raw|qcow2|qed] and
-netdev [user|tap|bridge] ...
-net [nic|user|tap|bridge|none] ... (for model= only rtl8139, e1000 and virtio
-tpmdev passthrough ...
- The following monitor commands are supported:
balloon target ...
change device ...
- The following command line options are unsupported:
(the following are aliases of these supported devices: lsi)
(note that some of these device names represent supported devices and
are used internally, but not specifyable via -device)
-drive ,if=[scsi|mtd|pflash], snapshot=on, format=[anything besides raw,
qcow2, or qed]
-netdev [socket|dump|vde|hubport] ...
-net [socket|dump|vde] ...
- The following monitor commands are unsupported:
nbd server_start ...
- The following QMP commands are supported:
- The following QMP commands are unsupported: