% Support statement for this release

This document describes the support status
and in particular the security support status of the Xen branch
within which you find it.

See the bottom of the file
for the definitions of the support status levels etc.

# Release Support

    Xen-Version: 4.22-rc
    Initial-Release: n/a
    Supported-Until: TBD
    Security-Support-Until: Unreleased - not yet security-supported

Release Notes
: <a href="https://wiki.xenproject.org/wiki/Xen_Project_X.YY_Release_Notes">RN</a>

# Feature Support

## Kconfig

EXPERT and DEBUG Kconfig options are not security supported. Other
Kconfig options are supported, if the related features are marked as
supported in this document.

## Host Architecture

### x86-64

    Status: Supported
    Status, Xeon Phi: Not supported.

### ARM v7 + Virtualization Extensions

    Status: Supported

### ARM v8

    Status, Xen in AArch64 mode: Supported
    Status, Xen in AArch32 mode: Tech Preview
    Status, Xen in Armv8-R: Experimental
    Status, Cortex A57 r0p0-r1p1: Supported, not security supported
    Status, Cortex A77 r0p0-r1p0: Supported, not security supported

For the Cortex A57 r0p0 - r1p1, see Errata 832075.
For the Cortex A77 r0p0 - r1p0, see Errata 1508412.

## Host hardware support

### ACPI CPU Hotplug

    Status, x86: Experimental

### Physical Memory

    Status, x86: Supported up to 12 TiB. Hosts with more memory are supported, but not security supported.
    Status, Arm32: Supported up to 12 GiB
    Status, Arm64: Supported up to 2 TiB

### Physical Memory Hotplug

    Status, x86: Supported

### Physical CPUs

    Status, x86: Supported up to 4096
    Status, ARM: Supported up to 128

### Host ACPI (via Domain 0)

    Status, x86 PV: Supported
    Status, ARM: Experimental

### Host EFI Boot

    Status, x86: Supported
    Status, Arm64: Supported

### Host EFI Secure Boot

    Status, x86: Experimental
    Status, Arm64: Experimental

### x86/Intel Platform QoS Technologies

    Status: Tech Preview

### IOMMU

    Status, AMD IOMMU: Supported
    Status, Intel VT-d: Supported
    Status, ARM SMMUv1: Supported, not security supported
    Status, ARM SMMUv2: Supported, not security supported
    Status, ARM SMMUv3: Tech Preview
    Status, Renesas IPMMU-VMSA: Supported, not security supported

### ARM/GICv3

GICv3 is an interrupt controller specification designed by Arm.

    Status, Arm64: Security supported
    Status, Arm32: Supported, not security supported

### ARM/GICv3 ITS

Extension to the GICv3 interrupt controller to support MSI.

    Status: Experimental

### ARM/Partial Emulation

Enable partial emulation of registers, otherwise considered unimplemented,
that would normally trigger a fault injection.

    Status: Supported, with caveats

Only the following system registers are security supported:

  * MDCCSR_EL0
  * DBGDTR_EL0
  * DBGDTRTX_EL0
  * DBGDTRRX_EL0
  * DBGDSCRINT
  * DBGDTRTXINT
  * DBGDTRRXINT

### ARM Scalable Vector Extension (SVE/SVE2)

Arm64 domains can use Scalable Vector Extension (SVE/SVE2).

    Status: Tech Preview

## Guest Type

### x86/PV

Traditional Xen PV guest

No hardware requirements

    Status, x86_64: Supported
    Status, x86_32, shim: Supported
    Status, x86_32, without shim: Supported, not security supported

### x86/HVM

Fully virtualised guest using hardware virtualisation extensions

Requires hardware virtualisation support (Intel VMX / AMD SVM)

    Status, domU: Supported

### x86/PVH

PVH is a next-generation paravirtualized mode
designed to take advantage of hardware virtualization support when possible.
During development this was sometimes called HVMLite or PVHv2.

Requires hardware virtualisation support (Intel VMX / AMD SVM).

Dom0 support requires an IOMMU (Intel VT-d / AMD IOMMU).

    Status, domU: Supported
    Status, dom0: Supported, with caveats

PVH dom0 hasn't received the same test coverage as PV dom0, so it can exhibit
unexpected behavior or issues on some hardware.

At least the following features are missing on a PVH dom0:

  * PCI SR-IOV.

  * Native NMI forwarding (nmi=dom0 command line option).

  * MCE handling.

  * PCI Passthrough to any kind of domUs.

### ARM

ARM only has one guest type at the moment

    Status: Supported

## Guest Limits

### Memory

    Status, x86: Supported up to 8 TiB. Guests with more memory, but less than 16 TiB, are supported, but not security supported.
    Status, Arm32: Supported up to 12 GiB
    Status, Arm64: Supported up to 1 TiB

## Hypervisor file system

### Build info

    Status: Supported

### Hypervisor config

    Status: Supported

### Runtime parameters

    Status: Supported

## Toolstack

While 32-bit builds of the tool stack are generally supported, restrictions
apply in particular when running on top of a 64-bit hypervisor.  For example,
very large guests aren't expected to be manageable in this case.  This includes
guests giving the appearance of being large, by altering their own memory
layouts.

### xl

    Status: Supported

### Direct-boot kernel image format

Format which the toolstack accepts for direct-boot kernels

    Supported, x86: bzImage, ELF
    Supported, ARM32: zImage
    Supported, ARM64: Image

### Dom0 init support for xl

    Status, SysV: Supported
    Status, systemd: Supported
    Status, BSD-style: Supported

### JSON output support for xl

Output of information in machine-parseable JSON format

    Status: Experimental

### Open vSwitch integration for xl

    Status, Linux: Supported

### Virtual cpu hotplug

    Status: Supported

### QEMU backend hotplugging for xl

    Status: Supported

### xenlight Go package

Go (golang) bindings for libxl

    Status: Experimental

### Linux device model stubdomains

Support for running qemu-xen device model in a linux stubdomain.

    Status: Supported, with caveats

Any issue in the stubdomain affecting only the guest it is servicing
or itself will not be regarded a security issue.

## Xenstore

### C xenstored daemon

    Status: Supported
    Status, Liveupdate: Supported

### C xenstore stubdom PV

    Status: Supported
    Status, Liveupdate: Not implemented

### C xenstore stubdom PVH

    Status: Supported
    Status, Liveupdate: Supported

### OCaml xenstored daemon

    Status: Supported
    Status, untrusted driver domains: Supported, not security supported
    Status, Liveupdate: Not functional

## Toolstack/3rd party

### libvirt driver for xl

    Status: Supported, Security support external

## Debugging, analysis, and crash post-mortem

### Host serial console

    Status, NS16550: Supported
    Status, EHCI: Supported
    Status, Cadence UART (ARM): Supported
    Status, PL011 UART (ARM): Supported
    Status, Exynos 4210 UART (ARM): Supported
    Status, OMAP UART (ARM): Supported
    Status, SCI(F) UART: Supported

### Hypervisor 'debug keys'

These are functions triggered either from the host serial console,
or via the xl 'debug-keys' command,
which cause Xen to dump various hypervisor state to the console.

    Status: Supported, not security supported

### Hypervisor synchronous console output (sync_console)

Xen command-line flag to force synchronous console output.

    Status: Supported, not security supported

Useful for debugging, but not suitable for production environments
due to incurred overhead.

### gdbsx

    Status, x86: Supported, not security supported

Debugger to debug ELF guests

### Soft-reset for PV guests

Soft-reset allows a new kernel to start 'from scratch' with a fresh VM state,
but with all the memory from the previous state of the VM intact.
This is primarily designed to allow "crash kernels",
which can do core dumps of memory to help with debugging in the event of a crash.

    Status: Supported

### xentrace

Tool to capture Xen trace buffer data

    Status, x86: Supported

### gcov

Export hypervisor coverage data suitable for analysis by gcov or lcov.

    Status: Supported, Not security supported

### Processor trace support

Support for using Intel Processor Trace technology to trace guests
from dom0.

    Status, x86: Tech Preview

## Memory Management

### Dynamic memory control

Allows a guest to add or remove memory after boot-time.
This is typically done by a guest kernel agent known as a "balloon driver".

    Status: Supported

### Populate-on-demand memory

This is a mechanism that allows normal operating systems with only a balloon driver
to boot with memory < maxmem.

    Status, x86 HVM: Supported

### Static Allocation

Static allocation refers to domains for which memory areas are
pre-defined by configuration using physical address ranges.

    Status, ARM: Tech Preview

### Static Heap

Allow reserving parts of RAM through the device tree using physical
address ranges as heap.

    Status, ARM: Tech Preview

### Memory Sharing

Allow sharing of identical pages between guests

    Status, x86 HVM: Experimental

### Static Memory Sharing

Allow to statically set up shared memory on dom0less system,
enabling domains to do shm-based communication

    Status, ARM: Tech Preview

### Memory Paging

Allow pages belonging to guests to be paged to disk

    Status, x86 HVM: Experimental

### Alternative p2m

Alternative p2m (altp2m) allows external monitoring of guest memory
by maintaining multiple physical to machine (p2m) memory mappings.

    Status, x86 HVM: Tech Preview
    Status, ARM: Tech Preview

### Cache coloring

Allows to reserve Last Level Cache (LLC) partitions for Dom0, DomUs and Xen
itself.

    Status, Arm64: Experimental

## Resource Management

### CPU Pools

Groups physical cpus into distinct groups called "cpupools",
with each pool having the capability
of using different schedulers and scheduling properties.

    Status: Supported

### Core Scheduling

Allows to group virtual cpus into virtual cores which are scheduled on the
physical cores. This results in never running different guests at the same
time on the same physical core.

    Status, x86: Experimental

### Credit Scheduler

A weighted proportional fair share virtual CPU scheduler.
This is the default scheduler.

    Status: Supported

### Credit2 Scheduler

A general purpose scheduler for Xen,
designed with particular focus on fairness, responsiveness, and scalability

    Status: Supported

### RTDS based Scheduler

A soft real-time CPU scheduler
built to provide guaranteed CPU capacity to guest VMs on SMP hosts

    Status: Experimental

### ARINC653 Scheduler

A periodically repeating fixed timeslice scheduler.

    Status: Supported

Currently only single-vcpu domains are supported.

### Null Scheduler

A very simple, very static scheduling policy
that always schedules the same vCPU(s) on the same pCPU(s).
It is designed for maximum determinism and minimum overhead
on embedded platforms and the x86 PV shim.

    Status: Experimental
    Status, x86/shim: Supported

### NUMA scheduler affinity

Enables NUMA aware scheduling in Xen

    Status, x86: Supported

## Scalability

### Super page support

NB that this refers to the ability of guests
to have higher-level page table entries point directly to memory,
improving TLB performance.
On ARM, and on x86 in HAP mode,
the guest has whatever support is enabled by the hardware.

This feature is independent
of the ARM "page granularity" feature (see below).

    Status, x86 HVM/PVH, HAP: Supported
    Status, x86 HVM/PVH, Shadow, 2MiB: Supported
    Status, ARM: Supported

On x86 in shadow mode, only 2MiB (L2) superpages are available;
furthermore, they do not have the performance characteristics
of hardware superpages.

### x86/PVHVM

This is a useful label for a set of hypervisor features
which add paravirtualized functionality to HVM guests
for improved performance and scalability.
This includes exposing event channels to HVM guests.

    Status: Supported

## High Availability and Fault Tolerance

### Remus Fault Tolerance

    Status: Experimental

### COLO Manager

    Status: Experimental

### x86/vMCE

Forward Machine Check Exceptions to appropriate guests

    Status: Supported

## Virtual driver support, guest side

### Blkfront

Guest-side driver capable of speaking the Xen PV block protocol

    Status, Linux: Supported
    Status, FreeBSD: Supported, Security support external
    Status, NetBSD: Supported, Security support external
    Status, OpenBSD: Supported, Security support external
    Status, Windows: Supported, with caveats

Windows frontend currently trusts the backend;
bugs in the frontend which allow backend to cause mischief will not be
considered security vulnerabilities.

### Netfront

Guest-side driver capable of speaking the Xen PV networking protocol

    Status, Linux: Supported
    Status, FreeBSD: Supported, Security support external
    Status, NetBSD: Supported, Security support external
    Status, OpenBSD: Supported, Security support external
    Status, Windows: Supported, with caveats

Windows frontend currently trusts the backend;
bugs in the frontend which allow backend to cause mischief will not be
considered security vulnerabilities.

### PV Framebuffer (frontend)

Guest-side driver capable of speaking the Xen PV Framebuffer protocol

    Status, Linux (xen-fbfront): Supported, with caveats

Linux frontend currently trusts the backend;
bugs in the frontend which allow backend to cause mischief will not be
considered security vulnerabilities.

### PV display (frontend)

Guest-side driver capable of speaking the Xen PV display protocol

    Status, Linux, outside of "backend allocation" mode: Supported, with caveats
    Status, Linux, "backend allocation" mode: Experimental

Linux frontend currently trusts the backend;
bugs in the frontend which allow backend to cause mischief will not be
considered security vulnerabilities.

### PV Console (frontend)

Guest-side driver capable of speaking the Xen PV console protocol

    Status, Linux (hvc_xen): Supported
    Status, FreeBSD: Supported, Security support external
    Status, NetBSD: Supported, Security support external
    Status, Windows: Supported, with caveats

Windows frontend currently trusts the backend;
bugs in the frontend which allow backend to cause mischief will not be
considered security vulnerabilities.

### PV keyboard (frontend)

Guest-side driver capable of speaking the Xen PV keyboard protocol.
Note that the "keyboard protocol" includes mouse / pointer /
multi-touch support as well.

    Status, Linux (xen-kbdfront): Supported, with caveats

Linux frontend currently trusts the backend;
bugs in the frontend which allow backend to cause mischief will not be
considered security vulnerabilities.

### PV USB (frontend)

    Status, Linux: Supported, with caveats

Linux frontend currently trusts the backend;
bugs in the frontend which allow backend to cause mischief will not be
considered security vulnerabilities.

### PV SCSI protocol (frontend)

    Status, Linux: Supported, with caveats

NB that while the PV SCSI frontend is in Linux and tested regularly,
there is currently no xl support.

Linux frontend currently trusts the backend;
bugs in the frontend which allow backend to cause mischief will not be
considered security vulnerabilities.

### PV TPM (frontend)

Guest-side driver capable of speaking the Xen PV TPM protocol

    Status, Linux (xen-tpmfront): Tech Preview

### PV 9pfs frontend

Guest-side driver capable of speaking the Xen 9pfs protocol

    Status, Linux: Tech Preview

### PVCalls (frontend)

Guest-side driver capable of making pv system calls

    Status, Linux: Tech Preview

### PV sound (frontend)

Guest-side driver capable of speaking the Xen PV sound protocol

    Status, Linux: Supported, with caveats

Linux frontend currently trusts the backend;
bugs in the frontend which allow backend to cause mischief will not be
considered security vulnerabilities.

## Virtual device support, host side

For host-side virtual device support,
"Supported" and "Tech preview" include xl/libxl support
unless otherwise noted.

### Blkback

Host-side implementations of the Xen PV block protocol.

    Status, Linux (xen-blkback): Supported
    Status, QEMU (xen_disk), raw format: Supported
    Status, QEMU (xen_disk), qcow format: Supported
    Status, QEMU (xen_disk), qcow2 format: Supported
    Status, QEMU (xen_disk), vhd format: Supported
    Status, FreeBSD (blkback): Supported, Security support external
    Status, NetBSD (xbdback): Supported, security support external
    Status, Blktap2, raw format: Deprecated
    Status, Blktap2, vhd format: Deprecated

Backends only support raw format unless otherwise specified.

### Netback

Host-side implementations of Xen PV network protocol

    Status, Linux (xen-netback): Supported
    Status, FreeBSD (netback): Supported, Security support external
    Status, NetBSD (xennetback): Supported, Security support external

### PV Framebuffer (backend)

Host-side implementation of the Xen PV framebuffer protocol

    Status, QEMU: Supported

### PV Console (xenconsoled)

Host-side implementation of the Xen PV console protocol

    Status: Supported

### PV keyboard (backend)

Host-side implementation of the Xen PV keyboard protocol.
Note that the "keyboard protocol" includes mouse / pointer support as well.

    Status, QEMU: Supported

### PV USB (backend)

Host-side implementation of the Xen PV USB protocol

    Status, QEMU: Supported

### PV SCSI protocol (backend)

    Status, Linux: Experimental

NB that while the PV SCSI backend is in Linux and tested regularly,
there is currently no xl support.

### PV TPM (backend)

    Status: Tech Preview

### PV 9pfs (backend)

    Status, QEMU: Tech Preview
    Status, xen-9pfsd: Experimental

### PVCalls (backend)

    Status, Linux: Experimental

PVCalls backend has been checked into Linux,
but has no xl support.

### Online resize of virtual disks

    Status: Supported

## Security

### Driver Domains

"Driver domains" means allowing non-Domain 0 domains
with access to physical devices to act as back-ends.

    Status: Supported, with caveats

See the appropriate "Device Passthrough" section
for more information about security support.

### Device Model Stub Domains

    Status: Supported, with caveats

Vulnerabilities of a device model stub domain
to a hostile driver domain (either compromised or untrusted)
are excluded from security support.

### Device Model Deprivileging

    Status, Linux dom0: Tech Preview, with limited support

This means adding extra restrictions to a device model in order to
prevent a compromised device model from attacking the rest of the
domain it's running in (normally dom0).

"Tech preview with limited support" means we will not issue XSAs for
the _additional_ functionality provided by the feature; but we will
issue XSAs in the event that enabling this feature opens up a security
hole that would not be present without the feature disabled.

For example, while this is classified as tech preview, a bug in libxl
which failed to change the user ID of QEMU would not receive an XSA,
since without this feature the user ID wouldn't be changed. But a
change which made it possible for a compromised guest to read
arbitrary files on the host filesystem without compromising QEMU would
be issued an XSA, since that does weaken security.

### KCONFIG Expert

    Status: Experimental

### Live Patching

    Status, x86: Supported
    Status, ARM: Experimental

Compile time disabled for ARM by default.

### Virtual Machine Introspection

    Status, x86: Supported, not security supported

### XSM (Xen Security Module) Framework

XSM is a security policy framework.  The dummy implementation is covered by this
statement, and implements a policy whereby dom0 is all powerful.  See below for
alternative modules (FLASK, SILO).

    Status: Supported

### FLASK XSM Module

    Status: Experimental

Compile time disabled by default.

Also note that using FLASK
to delegate various domain control hypercalls
to particular other domains, rather than only permitting use by dom0,
is also specifically excluded from security support for many hypercalls.
Please see XSA-77 for more details.

### FLASK default policy

    Status: Experimental

The default policy includes FLASK labels and roles for a "typical" Xen-based system
with dom0, driver domains, stub domains, domUs, and so on.

### SILO XSM Module

SILO extends the dummy policy by enforcing that DomU-s can only communicate
with Dom0, yet not with each other.

    Status: Supported

## Virtual Hardware, Hypervisor

### x86/Nested PV

This means running a Xen hypervisor inside an HVM domain on a Xen system,
with support for PV L2 guests only
(i.e., hardware virtualization extensions not provided
to the guest).

    Status, x86 Xen HVM: Tech Preview

This works, but has performance limitations
because the L1 dom0 can only access emulated L1 devices.

Xen may also run inside other hypervisors (KVM, Hyper-V, VMWare),
but nobody has reported on performance.

### x86/Nested HVM

This means providing hardware virtulization support to guest VMs
allowing, for instance, a nested Xen to support both PV and HVM guests.
It also implies support for other hypervisors,
such as KVM, Hyper-V, Bromium, and so on as guests.

    Status, x86 HVM: Experimental

### vPMU

Virtual Performance Management Unit

    Status, x86 HVM: Supported, Not security supported
    Status, ARM: Experimental

On ARM, support for accessing PMU registers from the guests.
There is no interrupt support and Xen will not save/restore
the register values on context switches.

Disabled by default.
On ARM, enable with guest parameter.
On x86, enable with hypervisor command line option.

This feature is not security supported: see https://xenbits.xen.org/xsa/advisory-163.html

### Argo: Inter-domain message delivery by hypercall

    Status: Tech Preview

### x86/PCI Device Passthrough

    Status, x86 PV: Supported, with caveats
    Status, x86 HVM: Supported, with caveats

Only systems using IOMMUs are supported.

Passing through of devices sharing resources with another device is not
security supported.  Such sharing could e.g. be the same line interrupt being
used by multiple devices, one of which is to be passed through, or two such
devices having memory BARs within the same 4k page.

Not compatible with migration, populate-on-demand, altp2m,
introspection, memory sharing, or memory paging.

Because of hardware limitations
(affecting any operating system or hypervisor),
it is generally not safe to use this feature
to expose a physical device to completely untrusted guests.
However, this feature can still confer significant security benefit
when used to remove drivers and backends from domain 0
(i.e., Driver Domains).

### x86/Multiple IOREQ servers

An IOREQ server provides emulated devices to HVM and PVH guests.
QEMU is normally the only IOREQ server,
but Xen has support for multiple IOREQ servers.
This allows for custom or proprietary device emulators
to be used in addition to QEMU.

	Status: Experimental

### ARM/IOREQ servers

	Status: Tech Preview

### ARM/Non-PCI device passthrough

    Status: Supported, not security supported

Note that this still requires an IOMMU
that covers the DMA of the device to be passed through.

### ARM: 16K and 64K page granularity in guests

    Status: Supported, with caveats

No support for QEMU backends in a 16K or 64K domain.

### ARM: Firmware Framework for Arm A-profile (FF-A) Mediator

    Status, Arm64: Tech Preview

There are still some code paths where a vCPU may hog a pCPU longer than
necessary. The FF-A mediator is not yet implemented for Arm32. Part of the
FF-A specification is not supported, see the top comment in
xen/arch/arm/tee/ffa.c for limitations.

### ARM: Guest Device Tree support

    Status: Supported

### Device Tree Overlays

Add/Remove device tree nodes using a device tree overlay binary (.dtbo).

    Status, ARM: Experimental

### ARM: Guest ACPI support

    Status: Supported

### Arm: OP-TEE Mediator

    Status: Tech Preview

### Arm: SCMI over SMC calls forwarding to EL3 Firmware

Enable SCMI calls using SMC as doorbell mechanism and Shared Memory for
transport ("arm,scmi-smc" compatible only) to reach EL3 Firmware if issued
by hwdom. Some platforms use SCMI for access to system-level resources.

    Status: Supported

### ARM: Guest PSCI support

Emulated PSCI interface exposed to guests. We support all mandatory
functions of PSCI 1.1. See below for the list of optional PSCI call
implemented and their status.

    Status, Mandatory: Supported
    Status, MIGRATE_INFO_TYPE: Supported
    Status, SYSTEM_SUSPEND: Tech Preview

## Virtual Hardware, QEMU

This section describes supported devices available in HVM mode using a
qemu devicemodel (the default).

    Status: Support scope restricted 

Note that other devices are available but not security supported.

### x86/Emulated platform devices (QEMU):

    Status, piix3: Supported

### x86/Emulated network (QEMU):

    Status, e1000: Supported
    Status, rtl8193: Supported
    Status, virtio-net: Supported

### x86/Emulated storage (QEMU):

    Status, piix3 ide: Supported
    Status, ahci: Supported

See the section **Blkback** for image formats supported by QEMU.

### x86/Emulated graphics (QEMU):

    Status, cirrus-vga: Supported
    Status, stdvga: Supported

### x86/Emulated audio (QEMU):

    Status, sb16: Supported
    Status, es1370: Supported
    Status, ac97: Supported

### x86/Emulated input (QEMU):

    Status, usbmouse: Supported
    Status, usbtablet: Supported
    Status, ps/2 keyboard: Supported
    Status, ps/2 mouse: Supported

### x86/Emulated serial card (QEMU):

    Status, UART 16550A: Supported

### x86/Host USB passthrough (QEMU):

    Status: Supported, not security supported

## Virtual Firmware

### x86/HVM iPXE

Booting a guest via PXE.

    Status: Supported, with caveats

PXE inherently places full trust of the guest in the network,
and so should only be used
when the guest network is under the same administrative control
as the guest itself.

### x86/HVM BIOS

Booting a guest via guest BIOS firmware

    Status, SeaBIOS (qemu-xen): Supported

### x86/HVM OVMF

OVMF firmware implements the UEFI boot protocol.

    Status, qemu-xen: Supported

## Dom0less

Guest creation from the hypervisor at boot without Dom0 intervention.

    Status, ARM: Supported

Memory of dom0less DomUs is not scrubbed at boot when bootscrub=on or
bootscrub=off are passed as Xen command line parameters. (Memory should
be scrubbed with bootscrub=idle.) No XSAs will be issues due to
unscrubbed memory.

## Static Event Channel

Allow to setup the static event channel on dom0less system, enabling domains
to send/receive notifications.

    Status, ARM: Tech Preview

# Format and definitions

This file contains prose, and machine-readable fragments.
The data in a machine-readable fragment relate to
the section and subsection in which it is found.

The file is in markdown format.
The machine-readable fragments are markdown literals
containing RFC-822-like (deb822-like) data.

In each case, descriptions which expand on the name of a feature as
provided in the section heading, precede the Status indications.
Any paragraphs which follow the Status indication are caveats or
qualifications of the information provided in Status fields.

## Keys found in the Feature Support subsections

### Status

This gives the overall status of the feature,
including security support status, functional completeness, etc.
Refer to the detailed definitions below.

If support differs based on implementation
(for instance, x86 / ARM, Linux / QEMU / FreeBSD),
one line for each set of implementations will be listed.

## Definition of Status labels

Each Status value corresponds to levels of security support,
testing, stability, etc., as follows:

### Experimental

    Functional completeness: No
    Functional stability: Here be dragons
    Interface stability: Not stable
    Security supported: No

### Tech Preview

    Functional completeness: Yes
    Functional stability: Quirky
    Interface stability: Provisionally stable
    Security supported: No

#### Supported

    Functional completeness: Yes
    Functional stability: Normal
    Interface stability: Yes
    Security supported: Yes

#### Deprecated

    Functional completeness: Yes
    Functional stability: Quirky
    Interface stability: No (as in, may disappear the next release)
    Security supported: Yes

All of these may appear in modified form.
There are several interfaces, for instance,
which are officially declared as not stable;
in such a case this feature may be described as "Stable / Interface not stable".

## Definition of the status label interpretation tags

### Functionally complete

Does it behave like a fully functional feature?
Does it work on all expected platforms,
or does it only work for a very specific sub-case?
Does it have a sensible UI,
or do you have to have a deep understanding of the internals
to get it to work properly?

### Functional stability

What is the risk of it exhibiting bugs?

General answers to the above:

  * **Here be dragons**

    Pretty likely to still crash / fail to work.
    Not recommended unless you like life on the bleeding edge.

  * **Quirky**

    Mostly works but may have odd behavior here and there.
    Recommended for playing around or for non-production use cases.

  * **Normal**

    Ready for production use

### Interface stability

If I build a system based on the current interfaces,
will they still work when I upgrade to the next version?

  * **Not stable**

    Interface is still in the early stages and
    still fairly likely to be broken in future updates.

  * **Provisionally stable**

    We're not yet promising backwards compatibility,
    but we think this is probably the final form of the interface.
    It may still require some tweaks.

  * **Stable**

    We will try very hard to avoid breaking backwards  compatibility,
    and to fix any regressions that are reported.

### Security supported

Will XSAs be issued if security-related bugs are discovered
in the functionality?

If "no",
anyone who finds a security-related bug in the feature
will be advised to
post it publicly to the Xen Project mailing lists
(or contact another security response team,
if a relevant one exists).

Bugs found after the end of **Security-Support-Until**
in the Release Support section will receive an XSA
if they also affect newer, security-supported, versions of Xen.
However, the Xen Project will not provide official fixes
for non-security-supported versions.

Three common 'diversions' from the 'Supported' category
are given the following labels:

  * **Supported, Not security supported**

    Functionally complete, normal stability,
    interface stable, but no security support

  * **Supported, Security support external**

    This feature is security supported
    by a different organization (not the XenProject).
    The extent of support is defined by that organization.
    It might be limited, e.g. like described in **Supported, with caveats**
    below.
    See **External security support** below.

  * **Supported, with caveats**

    This feature is security supported only under certain conditions,
    or support is given only for certain aspects of the feature,
    or the feature should be used with care
    because it is easy to use insecurely without knowing it.
    Additional details will be given in the description.

### Interaction with other features

Not all features interact well with all other features.
Some features are only for HVM guests; some don't work with migration, &c.

### External security support

The XenProject security team
provides security support for XenProject projects.

We also provide security support for Xen-related code in Linux,
which is an external project but doesn't have its own security process.

External projects that provide their own security support for Xen-related features are listed below.

  * QEMU https://wiki.qemu.org/index.php/SecurityProcess

  * Libvirt https://libvirt.org/securityprocess.html

  * FreeBSD https://www.freebsd.org/security/

  * NetBSD http://www.netbsd.org/support/security/

  * OpenBSD https://www.openbsd.org/security.html
