Xen Project Release Features

Legend: ✓: Feature ✓: Partial

	Xen 4.0	Xen 4.1	Xen 4.2	Xen 4.3	Xen 4.4	Xen 4.5
Initial Release	7 April 2010	25 March 2011	17 Sept 2012	9 July 2013	10 March 2014	15 Jan 2015
Feature List			FL 4.2	FL 4.3	FL 4.4	FL 4.5
Release Notes	RN 4.0	RN 4.1	RN 4.2	RN 4.3	RN 4.4	RN 4.5
Supported Mainline Architectures for the hypervisor (Host)
IA-A32	✓	✓	✓	✗removed
X86-64	✓	✓	✓	✓	✓	✓
Itanium (ia64)	✓	✓deprecated in this release	✓deprecated	✗removed
ARM v7 + Virtualization Extensions				✓preview [ 6 ]	✓	✓ [ 8 ]
ARM v8				✓preview [ 6 ]	✓	✓ [ 9 ]
Guest Types
For X86 Architectures
Paravirtualised Traditional Xen Project PV guest	✓	✓	✓	✓	✓	✓
HVM Guest [ 1 ] Fully virtualised guest using hardware virtualisation extensions	✓	✓	✓	✓	✓	✓
PV-on-HVM Guest [ 1 ] Fully virtualised guest using PV extensions/drivers for improved performance	✓	✓	✓	✓	✓	✓
PVH Guest					✓preview	✓preview added PVH Dom0
For ARM Architectures
ARM Guest Optimal combination of full virtualization and PV extensions				✓preview [ 6 ]	✓	✓
Host Limits
For X86 Architectures
Physical CPUs	128 [ 0 ]	>255	4095	4095	4095	4095
Physical RAM	1TB	5TB	5TB	16TB	16TB	16TB
For ARM Architectures
Physical CPUs				8	8	8
Physical RAM				16GB	16GB	16GB for 32bit, 5TB for 64bit
Guest Limits
X86 PV Guest Limits
Virtual CPUs	128	>255	512	512	512	512
Virtual RAM	512GB	512GB	512GB	512GB	512GB	512GB
X86 HVM Guest Limits
Virtual CPUs	128	128	256	256	256	256
Virtual RAM	1TB	1TB	1TB	1TB	1TB	1TB
ARM Guest Limits
Virtual CPUs				8	8	8
Virtual RAM				16GB	16GB	1TB [ 7 ]
Number of event channels
Event Channels	1024/4096	1024/4096	1024/4096	1024/4096	131072	131072
Toolstack
Built-in
xend / xm	✓	✓	✓deprecated in this release	✓deprecated	✓deprecated	✗removed
XL	✓initial implementation	✓preview release	✓	✓	✓	✓
Qemu based disk backend (qdisk) for XL		✓ [ 5 ]	✓ [ 5 ]	✓ [ 5 ]	✓ [ 5 ]	✓ [ 5 ]
XL Open vSwitch integration				✓preview	✓	✓
systemd support						✓
JSON support						✓infrastructure only, no tools support
3rd Party
libvirt driver for XL		✓	✓	✓	✓	✓
Features
Advanced Memory Management
Memory Ballooning	✓	✓	✓	✓	✓	✓
Memory Sharing allow sharing of identical pages between HVM guests	✓preview	✓preview	✓preview [ 3 ]	✓preview [ 3 ]	✓preview [ 3 ]	✓preview [ 3 ][ 12 ]
Memory Paging allow pages belonging to HVM guests to be paged to disk	✓preview	✓preview	✓preview [ 3 ]	✓preview [ 3 ]	✓preview [ 3 ]	✓preview [ 3 ][ 12 ]
TMEM - Transcendent Memory	✓experimental [ 2 ]	✓experimental [ 2 ]	✓experimental [ 2 ]	✓experimental [ 2 ]	✓experimental [ 2 ]	✓experimental [ 2 ][ 12 ]
Resource Management
Cpupool advanced partitioning		✓	✓	✓	✓	✓
Credit 2 Scheduler designed for latency-sensitive workloads and very large systems.		✓prototype	✓prototype	✓experimental	✓experimental	✓experimental
RTDS Based Scheduler Real-time CPU scheduler built to provide guaranteed CPU capacity to guest VMs on SMP hosts.						✓experimental
NUMA scheduler affinity				✓	✓	✓ [ 12 ]
Scalability
1GB/2MB super page support		✓	✓	✓	✓	✓
Deliver events to PVHVM guests using Xen event channels		✓	✓	✓	✓	✓
Interoperability / Hardware Support
X86 Nested Virtualisation Running a hypervisor inside an HVM guest			✓experimental	✓experimental	✓preview	✓preview [ 11 ]
HVM PXE Stack (x86)	gPXE	iPXE	iPXE	iPXE	iPXE	iPXE
Physical CPU Hotplug	✓	✓	✓	✓	✓	✓[ 12 ]
Physical Memory Hotplug	✓	✓	✓	✓	✓	✓[ 12 ]
Support for PV kernels in bzImage format	✓	✓	✓	✓	✓	✓[ 12 ]
PCI Passthrough	✓	✓	✓	✓ [ 12 ]	✓ [ 12 ]	✓ [ 12 ][ 13 ]
X86 Advanced Vector eXtension (AVX)		✓ [ 4 ]	✓	✓	✓	✓
X86 Cache Monitoring Technology (CMT)						✓ preview [ 14 ]
High Availability and Fault Tolerance
Live Migration, Save & Restore	✓	✓	✓	✓	✓	✓ [ 12 ]
Remus Fault Tolerance	✓	✓	✓	✓	✓	✓ improvements for COLO [ 10 ][ 12 ]
X86 vMCE Forward Machine Check Exceptions to Appropriate guests			✓	✓	✓	✓
Network and Storage
Blktap2	✓	✓	✓	✓	✓	✓
Online resize of virtual disks	✓	✓	✓	✓	✓	✓
Security (also see this presentation or this document)
Driver Domains	✓	✓	✓	✓	✓	✓
Device Model Stub Domains	✓	✓	✓	✓	✓	✓[ 12 ]
Virtual Machine Introspection (Memaccess API) enabling integration of 3rd party security solutions into Xen virtualized environments		✓	✓	✓	✓	✓ improvements[ 12 ]
XSM & FLASK mandatory access control policy providing fine-grained controls over Xen domains, similar to SELinux	✓	✓	✓	✓	✓	✓
XSM & FLASK support for IS_PRIV				✓	✓	✓
vTPM Support	✓	✓	✓	✓ updates and new functionality	✓	✓
Tooling
gdbsx debugger to debug ELF guests	✓	✓	✓	✓	✓	✓[ 12 ]
vPMU Virtual Performance Management Unit for HVM guests	✓ [ 4 ]	✓ [ 4 ]	✓ [ 4 ]	✓ [ 4 ]	✓ [ 4 ]	✓ [ 4 ][ 12 ]
Serial console	✓	✓	✓	✓Add EHCI debug support	✓	✓Add Oxford PCIe, and Broadcom TrueManage support
xentrace performance analysis	✓	✓	✓	✓	✓	✓[ 12 ]
Device Models and Virtual Firmware for HVM guests
For X86 Architectures
Traditional Device Model Device emulator based on Xen fork of Qemu	✓	✓	✓	✓	✓	✓
Qemu Upstream Device Model Device emulator based on upstream Qemu			✓preview	✓default, unless stubdomains are used	✓default, unless stubdomains are used	✓default, unless stubdomains are used
ROMBIOS BIOS used with traditional device model only	✓	✓	✓	✓	✓	✓
SeaBIOS BIOS used with upstream qemu device model and XL only			✓	✓	✓	✓
OVMF/Tianocore UEFI Firmware used with upstream qemu device model and XL only			✓experimental [ 4 ]	✓experimental [ 4 ]	✓experimental [ 4 ]	✓experimental [ 4 ]
PV Bootloader support
For X86 Architectures
PyGrub support for GRUB 2	✓	✓	✓	✓	✓	✓
PyGrub support for /boot on ext4	✓	✓	✓	✓	✓	✓
pvnetboot support Bootloader supporting network boot of PV guests			✓	✓	✓	✓

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^{[ 0 ]} Compile time limit, can be increased
^{[ 1 ]} Requires hardware virtualisation support
^{[ 2 ]} Disabled by default (enable with hypervisor command line option). Not supported in production and doesn't have full security support
^{[ 3 ]} Preview, due to limited tools support. Hypervisor side in good shape
^{[ 4 ]} Disabled by default (enable with hypervisor command line option)
^{[ 5 ]} Used as a fallback if blkback and/or blktap2 are not available
^{[ 6 ]} See Xen ARM with Virtualization Extensions; basic functionality implemented; lack of real hardware to validate against
^{[ 7 ]} Limited by supported host memory
^{[ 8 ]} Tested on Broadcom 7445D0 A15, Midway (Calxeda), Odroid-XU, OMAP5, OMAP6, DRA7 (Texas Instrument), Exynos5 (Samsung), SunXI (AllWinner) aka A20/A21, CubieTruck, CubieBoard
^{[ 9 ]} Tested on Vexpress (ARM Ltd.), Seattle (AMD), Mustang (Applied Micro-X-Gene), McDivitt aka HP Moonshot cartridge (Applied Micro X-Gene)
^{[ 10 ]} Remus has been ported to XL and has been tested with COLO which is currently outside the Xen tree, but planned to be included in Xen 4.6
^{[ 11 ]} There are a number of reported crashes that have not yet been fixed and some known limitations
^{[ 12 ]} Not yet supported on ARM; for a more detailed update on what is supported on ARM see here and here
^{[ 13 ]} The PCI passthrough features did not make it on time for Xen 4.5, but doing passthrough of MMIO regions did. In the ARM world it is quite common to have no PCIe devices and to only access devices using MMIO regions. As such this feature allows us to have driver domains be in charge of network or storage devices.
^{[ 14 ]} Not yet exposed in XL.