Xen Project Release Features

	Xen 4.0	Xen 4.1	Xen 4.2
Initial Release	7 April 2010	25 March 2011	17 September 2012
Host Limits
Physical CPUs	128 [ 0 ]	>255	4095
Physical RAM	1TB	5TB	5TB
Guest Types
Paravirtualised Traditional Xen 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	✓	✓	✓
PV Guest Limits
Virtual CPUs	128	>255	512
Virtual RAM	512GB	512GB	512GB
HVM Guest Limits
Virtual CPUs	128	128	256
Virtual RAM	1TB	1TB	1TB
Toolstack
xend / xm	✓	✓	✓deprecated in this release
XL	✓initial implementation	✓preview release	✓
Features
Live Migration, Save & Restore	✓	✓	✓
Memory ballooning	✓	✓	✓
Blktap2	✓	✓	✓
PCI Passthrough	✓	✓	✓
TMEM -- Transcendent Memory	✓ [ 2 ]	✓ [ 2 ]	✓ [ 2 ]
gdbsx debugger to debug ELF guests	✓	✓	✓
Memory Sharing allow sharing of identical pages between HVM guests	✓tech preview	✓tech preview	✓tech preview [ 3 ]
Memory Paging allow pages belonging to HVM guests to be paged to disk	✓tech preview	✓tech preview	✓tech preview [ 3 ]
Online resize of virtual disks	✓	✓	✓
Remus Fault Tolerance	✓	✓	✓
Physical CPU Hotplug	✓	✓	✓
Physical Memory Hotplug	✓	✓	✓
Support for PV kernels in bzImage format	✓	✓	✓
Credit 2 Scheduler designed for latency-sensitive workloads and very large systems.		✓prototype	✓prototype
1GB/2MB super page support		✓	✓
x86 Advanced Vector eXtension (AVX)		✓ [ 4 ]	✓ [ 4 ]
cpupool advanced partitioning		✓	✓
memaccess API enabling integration of 3rd party security solutions into Xen virtualized environments		✓	✓
Deliver events to PVHVM guests using Xen event channels		✓	✓
HVM PXE Stack	gPXE	iPXE	iPXE
xentrace performance analysis	✓	✓	✓
qemu based disk backend (qdisk) for XL		✓ [ 5 ]	✓ [ 5 ]
FLASK mandatory access control policy providing fine-grained controls over Xen domains, similar to SELinux	✓	✓	✓
vPMU Virtual Power Management Unit for HVM guests	✓	✓	✓
vMCE Forward Machine Check Exceptions to Appropriate guests	?	?	✓
Nested Virtualisation Running a hypervisor inside an HVM guest			✓
Device Models and Virtual Firmware for HVM guests
Traditional Device Model Device emulator based on Xen fork of Qemu	✓	✓	✓
Qemu Upstream Device Model Device emulator based on upstream Qemu			✓
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			✓
PV Bootloader support
PyGrub support for GRUB 2	✓	✓	✓
PyGrub support for /boot on ext4	✓	✓	✓
pvnetboot support Bootloader supporting network boot of PV guests			✓
Third Party
libvirt driver for XL		✓	✓

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^{[ 0 ]} Compile time limit, can be increased
^{[ 1 ]} Requires hardware virtualisation support
^{[ 2 ]} Ddisabled 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