Xen 4.6 发布，此版本专注于提高代码质量，安全加固，安全设备的启用，以及发布周期可预测性，主要更新内容分以下几方面： 详情请看发行说明。
General Hypervisor Updates The memory event subsystem has been reworked and extended to a new
VM event subsystem. The new VM event subsystems supports both the ARM
and x86 architectures. It can be used to intercept all sorts of VM
events, such as memory access, register access and more. This enables
security applications such as zero-footprint guest introspection,
host-wide monitoring and many others. Have a look at Tamas’s presentations and Steve’s presentations on this topic to get more insights. The Xen Security Modules
(XSM) now have a default policy that is regularly tested in the Xen
Project Test Lab to make sure it is not broken by mistake. This will
enable us to switch on XSM by default in the future. vTPM 2.0 support has been contributed by Intel and the US National
Security Agency. To learn more about how to use vTPM and how it can make
your host more secure, go to our wiki. Grant table scalability has been improvement significantly by using
finer-grained locks in grant tables. In some scenarios aggregate
intrahost network throughput has been shown to improve by 100%. Other
I/O drivers in Xen should potentially show significant performance
improvements as well. We introduced ticket lock to improve fairness, which provides better
support of massive workloads from up to hundreds or thousands of VMs on
a single host. The unused SEDF scheduler has been removed from the hypervisor and
toolstack. The Xen Project is committed to actively remove unused code
to keep the code base small and to minimize security risks. We removed Mini-OS
from the Xen code base into its own tree. Mini-OS started as a
demonstration OS, but received significant contributions in recent years
(e.g. it is used by many Unikernels). We decide to treat it as a
separately maintained independent project with it’s own mailing list and
code tree to make it easier to consume. We hope this will help
unikernel communities to more easily consume and contribute to Mini-OS,
while reducing the Xen Project Hypervisor footprint.
x86-specific Hypervisor Updates The Intel alternate P2M framework is a new capability for VM
Introspection, Security and Privacy in Xen that gives Xen the ability to
host up to 10 alternate guest to physical memory domains mappings for a
specific guest-domain. It is one of the key technologies to enable zero-footprint VM introspection. It can also help Xen to implement faster NFV applications. Intel Page Modification Logging Technology offloads the page dirty
logging duty to hardware. Microbenchmark shows about 7% improvement in
SPECJbb and should be particularly beneficial for Live Migration. Intel Cache Allocation Technology
allows system administrators to assign more L3 cache capacity to
individual VMs, resulting in lower latency and higher performance for
high-priority workloads such as NFV, real-time and video-on-demand
applications. Intel Memory Bandwidth Monitoring
allows system administrators to identify memory bandwidth saturation on
a Xen host that may be caused by several memory-intensive VMs running
on the same host. Taking corrective actions, such as migrating VMs to a
different Xen host, increases scalability and performance in the data
center. Intel Reserve Memory Region reporting provides a mechanism to report
and reserve memory regions for legacy devices to allow for safe device
passthrough. Virtual Performance Monitoring Unit support makes it possible to
profile the Xen Project Hypervisor with the Linux perf tool. Note that
some work still needs to be completed within Linux to make perf fully
functional. Virtual NUMA for HVM guest is a continuation of the NUMA work
performed in Xen 4.5 and previous releases. In this release, we exposed
the functionality through the XL toolstack and added firmware changes to
make the feature fully functional.
ARM-specific Hypervisor Updates The supported number of VCPUs has been increased from 8 to 128 VCPUs on ARM64 platforms. Passthrough for non-PCI devices allows users to passthrough devices
via partial device trees. Full support for PCI device passthrough is
currently being worked on. ARM GICv2 on GICv3 support. 32 bit userspace in 64 bit guest support. OVMF for ARM contributed by Linaro. 64K page ARM guest support. Support for the following new Hardware Platforms has been added:
Renesas R-Car Gen2, Thunder X, Huawei hip04-d04 and Xilinx ZynqMP SoC.
Toolstack Updates Live Migration support in libxc / libxl and has been replaced with a
completely new implementation (Migration v2). The new version respects
different layers in the Xen Software stack and has been designed to be
more robust and extensible to better support next-generation
infrastructures and work planned in subsequent hypervisor releases. Remus – our High Availability solution – has been reworked and is now based on Migration v2. Libxl asynchronous operations can now be cancelled. This allows
libxl users to cancel long-running asynchronous operations and benefits
tool stacks such as libvirt and is beneficial for integration with cloud
orchestration stacks. Improved SPICE/QXL support. AHCI disk controller support. A new host I/O topology query interface gives upper layer in the
software stack the ability to identify the I/O topology of underlying
hardware platform. Addition of Xenalyze, which is a tool for analyzing Hypervisor trace
buffers and can be used for debugging and optimization, has been added
to the Xen Project codebase as a maintained feature.
Xen Project Test Lab Updates During the Xen 4.6 release cycle, the Xen Project created
an Advisory Board funded Continuous Integration Test Lab. It currently
has 24 hosts and is going to expanded in the future. This has led to
significant improvements in Xen code quality and has allowed the project
to expand automated test coverage. The number of test cases doubled
during the 4.6 cycle. Some interesting new test cases that have been
added are: XSM Stub Domain VM migration using libvirt between two hosts is now tested. Live Migration between hosts of different Xen versions is now tested
and will help identify any breakage in our migration code or
specification. Test with different disk formats such as QCOW2, VHD and raw format.
More test cases are in the pipeline, including test case
for OpenStack’s devstack, performance and scalability tests, FreeBSD
Dom0 etc. Linux, FreeBSD and other OSes During the Xen 4.6 release cycle, we made significant
improvements to major operating systems we rely on to improve
interoperability. Some highlights on Linux kernel development spanning
from Linux 3.18 to 4.3 were: Xen blkfront multiqueue and multipage ring support. Xen SCSI frontend and backend support. VPMU kernel support. Performance improvement in mmap call. P2M in PV guest can address 512GB or more.
For FreeBSD there were these improvements: Experimental PVH Dom0/DomU support. Removal of classic i386 PV port by FreeBSD developer John Baldwin. Blkfront indirect descriptor support by FreeBSD developer Colin Percival. Removal of broken FreeBSD specific blkfront/back extensions. ARM32 and ARM64 guest support are underway.
Greater Ecosystem
Xen 是一个开放源代码虚拟机监视器，由剑桥大学开发。它打算在单个计算机上运行多达100个满特征的操作系统。操作系统必须进行显式地修改（“移植”）以在Xen上运行（但是提供对用户应用的兼容性）。这使得Xen无需特殊硬件支持，就能达到高性能的虚拟化。 | 
