Nested Virtualization in Xen: Difference between revisions

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=== Introduction ===
== Introduction ==


Nested virtualization is the ability to run a hypervisor inside of a virtual machine. The hypervisor that runs on the real hardware is called a ''level 0'' or ''L0''; the hypervisor that runs as a guest on L0 is called ''level 1'' or ''L1''; a guest that runs on the L1 hypervisor is called a ''level 2'' or ''L2''.


Nested virtualization is a technology that has several potential applications:
As the virtualization becomes popular, there are more and more requirements for nested virtualization, which provides the capability to enable the virtual machines to start second level of virtual machines. For example, with nested virtualization, cloud vendors are able to migrate their own cloud to others without any modification.


* '''End-user virtualization for guests'''. With nested virtualization, users can run Windows 7's XP compatibility mode (VirtualPC), or install Bromium in guests.
Currently, we enabled the nested virtualization on Xen. We can boot up all popular VMMs as normal virtual machine (Xen, KVM, VMware Workstation, VMware ESX, Hyper-V, etc.) and all those VMMs are able to boot its own VM. Besides, with adding several critical nested features, we made a good progress in performance that the second level guest is almost same with first level guest: Performance optimization (virtual EPT, VMCS shadowing, etc.) has boosted Xen nested virtualization performance by 30%-500%.


* '''Development'''. Many developers have found testing and debugging hypervisor and dom0 code much easier when it's run inside a virtual machine.

* '''Deployment testing'''. When experimenting with deployment of large clouds, admins can create "virtual clouds", comprising dozens of virtual machines, to test how cloud orchestration software or other coordination and deployment layers will work at scale, without the need to actually have a large number of dedicated machines.

Running PV guests as an L2 has been supported in Xen since the introduction of HVM guests in Xen 3.0. Support for HVM guests as L2 guests is heavily dependent on architecture-specific support. Nested HVM on AMD CPUs is considered "experimental". Nested HVM on Intel CPUs, as of Xen 4.4, is considered "tech preview". For many common cases, it should work reliably and with low overhead. However, there are some important limitations, and we do not recommend that it be used in a production environment at this time.

Only 64-bit hypervisors are supported at this time.

See below for more details on tested hypervisior / guest combinations, and known issues on Intel CPUs.
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=== Abbreviation ===
== Quick-start guide ==

* Make sure you have the right support
** Xen 4.4 or later
** Intel CPU with EPT support

* Add the following to your config file:
<pre><nowiki>
hap=1
nestedhvm=1
</nowiki></pre>


== Abbreviation ==
{| border="1"
{| border="1"
|+
|+
Line 22: Line 45:
| L2 || The second level VM which boot up by L1
| L2 || The second level VM which boot up by L1
|-
|-
| XEN_on_XEN || L1 XEN based on L0 XEN
| XP_mode|| L1 WIN7 VirtualPC XP_mode on L0 XEN
|-
| VMware_ESX_on_XEN|| L1 VMware ESX Server on L0 XEN
|-
|-
|V||Verified to work
| VMware_Workstaion_on_XEN|| L1 VMware Workstation on L0 XEN
|-
|-
|V*||Works but buggy?
| Hyperv_on_XEN|| L1 WIN8 with Hyper-v feature enabled on L0 XEN
|-
|-
|X||Does not work
| XP_mode|| L1 WIN7 VirtualPC XP_mode on L0 XEN
|}
|}


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-------


=== How to use nested ===
== How to use nested ==
===== Booting Xen: =====
===== Booting Xen: =====
:Nested feature is added to Xen long time ago. But it is really ready to use only from last year. So it’s better to use the latest Xen,
:Nested feature is added to Xen long time ago. But it is really ready to use only from last year. So it’s better to use the latest Xen,
Line 43: Line 64:
</nowiki></pre>
</nowiki></pre>


:NB: When I write this Wiki, there are still two patches are missing in upstream Xen if you want to boot up VMware. You can get those patches from:
:NB: When I wrote this Wiki, there are still one patch is missing in upstream Xen if you want to boot up VMware and Hyper-v. You can get the patch from:
::http://www.gossamer-threads.com/lists/xen/devel/316994


::http://www.gossamer-threads.com/lists/xen/devel/316993
::http://www.gossamer-threads.com/lists/xen/devel/316993
Line 70: Line 90:
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=== Current status ===
== Current status ==


==== Testing environment: ====
==== Testing environment: ====
Line 78: Line 98:
! scope="col" |
! scope="col" |
! scope="col" | Version
! scope="col" | Version
|-
|L0 XEN|| git commit:58f5bcaf05621810f06bf5b3592e2ae87475053d
|-
|-
|L1 XEN ||git commit:e423b5cd60ff95ba3680e2e4a8440d4d19b2b13e
|L1 XEN ||git commit:e423b5cd60ff95ba3680e2e4a8440d4d19b2b13e
Line 99: Line 117:
</nowiki></pre>
</nowiki></pre>


==== Result: ====
==== Result with xen commit:58f5bcaf as L0: ====
{| border="1" cellpadding="2"
{| border="1" cellpadding="2"
! scope="col" width="150px" | L1\L2
! scope="col" width="150px" | L1\L2
Line 124: Line 142:


:V* means it works before, but buggy with latest Xen
:V* means it works before, but buggy with latest Xen

==== Result with xen 4.5.0-rc4 as L0: ====
{| border="1" cellpadding="2"
! scope="col" width="150px" | L1\L2
! scope="col" | XP_x86
! scope="col" | XP_x64
! scope="col" | RHEL6U4_x86
! scope="col" | RHEL6U4_x64
! scope="col" | WIN7_x86
! scope="col" | WIN7_x64
! scope="col" | WIN8_x86
! scope="col" | WIN8_x64
|-
|XEN||V||V||V||V||V||V||V||V
|-
|KVM||V||V||V||V||V||V||V||V
|-
|VMware-ESX||X blue screen||X blue screen||V||V||V||X blue screen||X blue screen||X blue screen
|-
|VMware-Workstation||X blue screen||X blue screen||X panic||X panic||X blue screen||X blue screen||X blue screen||X blue screen
|-
|Hyperv||X||X||X||X||X||X||X||X
|}

==== Result with xen 4.6.0-release as L0: ====
{| border="1" cellpadding="2"
! scope="col" width="150px" | L1\L2
! scope="col" | XP_x64
! scope="col" | RHEL6U4_x64
! scope="col" | WIN7_x64
! scope="col" | WIN8_x64
|-
|XEN||V||V||V||V
|-
|KVM||V||V||V||V
|-
|VMware-Workstation||X blue screen||X panic||X blue screen||X blue screen
|-
|Hyperv||X||X||X||X
|}

==== Result with xen 4.7-rc4 as L0: ====
{| border="1" cellpadding="2"
! scope="col" width="150px" | L1\L2
! scope="col" | XP_x64
! scope="col" | RHEL6U4_x64
! scope="col" | WIN7_x64
! scope="col" | WIN8_x64
! scope="col" | WIN8.1_x64
|-
|XEN||V||V||V||V||V
|-
|KVM||V||V||V||V||V
|-
|VMware-Workstation||X blue screen||X panic||X blue screen||X blue screen||X blue screen
|-
|Hyperv||X||X||X||X||X
|}

==== Result with xen 4.8-rc2 as L0: ====
{| border="1" cellpadding="2"
! scope="col" width="150px" | L1\L2
! scope="col" | RHEL7U2_x64
! scope="col" | WIN7_x64
! scope="col" | WIN8_x64
! scope="col" | WIN8.1_x64
|-
|XEN||V||X||X||X
|-
|KVM||X||X||X||X
|-
|VMware-Workstation||X panic||X||X||X
|-
|Hyperv||X||X||X||X
|}


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=== Know Issues ===
==== Result with xen 4.9.0 as L0: ====
{| border="1" cellpadding="2"
! scope="col" width="150px" | L1\L2
! scope="col" | RHEL7U3_x64
! scope="col" | WIN7_x64
! scope="col" | WIN8_x64
! scope="col" | WIN8.1_x64
|-
|XEN||X||X||X||X
|-
|KVM||X||X||X||X
|-
|VMware-Workstation||X panic||X||X||X
|-
|Hyperv||X||X||X||X
|}

==== Result with xen 4.10.0 as L0: ====
{| border="1" cellpadding="2"
! scope="col" width="150px" | L1\L2
! scope="col" | RHEL7U4_x64
! scope="col" | WIN7_x64
! scope="col" | WIN8_x64
! scope="col" | WIN8.1_x64
|-
|XEN||X||X||X||X
|-
|KVM||X||N/A||X||X
|-
|VMware-Workstation||X panic||X||X||X
|-
|Hyperv||X||X||X||X
|}

==== Result with xen 4.11-rc5 as L0: ====
{| border="1" cellpadding="2"
! scope="col" width="150px" | L1\L2
! scope="col" | RHEL7U5_x64
! scope="col" | WIN7_x64
! scope="col" | WIN8_x64
! scope="col" | WIN8.1_x64
|-
|XEN||X||X||X blue screen||X blue screen
|-
|KVM||X||N/A||X||X
|-
|VMware-Workstation||X panic||X||X||X
|-
|Hyperv||X||X||X||X
|}

== Know Issues ==




:1. Only L2 EPT/shadow on L1 EPT is working. L2 EPT/shadow on L1/shadow is not supported.
:1. Only L2 EPT/Shadow on L1 EPT is working. L2 EPT/Shadow on L1 Shadow is not supported.


:2. Virtual Box fails to boot on top of Xen (L1 panic while booting L2)
:2. Virtual Box fails to boot on top of Xen (L1 panic while booting L2)
Line 138: Line 282:
::using remote desktop to connect guest
::using remote desktop to connect guest
::or set full update mode in Qemu.
::or set full update mode in Qemu.

:4. Using populate-on-demand (memory!=maxmem) or guest paging in an L1 hypervisor for an L2 guest may deadlock the L0 hypervisor.
{{Warning|This means an L1 admin can DOS the L0 hypervisor. This is a potential security issue; for this reason, we do not recommend running nested virtualization in production yet.}}

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=== Not Tested ===
== Not Tested ==


:1. L1 stress test, performance test
:1. L1 stress test, performance test
Line 155: Line 303:


:2. Nested Virtualization Update from Intel http://www.slideshare.net/xen_com_mgr/nested-virtualization-update-from-intel
:2. Nested Virtualization Update from Intel http://www.slideshare.net/xen_com_mgr/nested-virtualization-update-from-intel

[[Category:HowTo]]
[[Category:Overview]]
[[Category:Manual]]

Latest revision as of 02:13, 7 July 2018

Introduction

Nested virtualization is the ability to run a hypervisor inside of a virtual machine. The hypervisor that runs on the real hardware is called a level 0 or L0; the hypervisor that runs as a guest on L0 is called level 1 or L1; a guest that runs on the L1 hypervisor is called a level 2 or L2.

Nested virtualization is a technology that has several potential applications:

  • End-user virtualization for guests. With nested virtualization, users can run Windows 7's XP compatibility mode (VirtualPC), or install Bromium in guests.
  • Development. Many developers have found testing and debugging hypervisor and dom0 code much easier when it's run inside a virtual machine.
  • Deployment testing. When experimenting with deployment of large clouds, admins can create "virtual clouds", comprising dozens of virtual machines, to test how cloud orchestration software or other coordination and deployment layers will work at scale, without the need to actually have a large number of dedicated machines.

Running PV guests as an L2 has been supported in Xen since the introduction of HVM guests in Xen 3.0. Support for HVM guests as L2 guests is heavily dependent on architecture-specific support. Nested HVM on AMD CPUs is considered "experimental". Nested HVM on Intel CPUs, as of Xen 4.4, is considered "tech preview". For many common cases, it should work reliably and with low overhead. However, there are some important limitations, and we do not recommend that it be used in a production environment at this time.

Only 64-bit hypervisors are supported at this time.

See below for more details on tested hypervisior / guest combinations, and known issues on Intel CPUs.

Quick-start guide

  • Make sure you have the right support
    • Xen 4.4 or later
    • Intel CPU with EPT support
  • Add the following to your config file:
    hap=1
    nestedhvm=1


Abbreviation

Abbreviation Description
L0 Xen hypervisor
L1 First level VM which is able to start second level VM
L2 The second level VM which boot up by L1
XP_mode L1 WIN7 VirtualPC XP_mode on L0 XEN
V Verified to work
V* Works but buggy?
X Does not work

How to use nested

Booting Xen:
Nested feature is added to Xen long time ago. But it is really ready to use only from last year. So it’s better to use the latest Xen,
    git clone git://xenbits.xen.org/xen.git xen.git
NB: When I wrote this Wiki, there are still one patch is missing in upstream Xen if you want to boot up VMware and Hyper-v. You can get the patch from:
http://www.gossamer-threads.com/lists/xen/devel/316993

Booting Dom0:

No special requirement for Dom0. Just use the stable one is enough.

QEMU:

Both Qemu-xen and Qemu traditional are OK.

L1 configuration:

To use nested virtualization, you need to add the following two lines in your guest configuration file:
    hap=1
    nestedhvm=1
NB: We don’t want to support L1 guest with shadow mode, since the performance is very poor. So I recommend you to enable the EPT(hap = 1) in the L1 guest. Besides, there is a known issue that nested is failing to work with L1 shadow mode.
To boot L1 VMware-ESX, VMware-Workstation, Win8-hyperv, you needs to mask CPU bit.
    cpuid = ['0x1:ecx=0xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx']

Current status

Testing environment:

Version
L1 XEN git commit:e423b5cd60ff95ba3680e2e4a8440d4d19b2b13e
L1 KVM 3.12.-rc2
L1 VMware Workstation 10.0
L1 VMware ESX 5.1
L1 Hyperv Win8 with hyperv feature enabled

L1 configuration:

    hap=1
    nestedhvm=1
    cpuid = ['0x1:ecx=0xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx']

Result with xen commit:58f5bcaf as L0:

L1\L2 XP_x86 XP_x64 RHEL6U4_x86 RHEL6U4_x64 WIN7_x86 WIN7_x64 WIN8_x86 WIN8_x64
XEN V V V V V V V V
KVM V V V V V V V V
VMware-ESX V V V V V V V V
VMware-Workstation V* V V V V* V V V
Hyperv V V V V V V V V
V means guest boots well
V* means it works before, but buggy with latest Xen

Result with xen 4.5.0-rc4 as L0:

L1\L2 XP_x86 XP_x64 RHEL6U4_x86 RHEL6U4_x64 WIN7_x86 WIN7_x64 WIN8_x86 WIN8_x64
XEN V V V V V V V V
KVM V V V V V V V V
VMware-ESX X blue screen X blue screen V V V X blue screen X blue screen X blue screen
VMware-Workstation X blue screen X blue screen X panic X panic X blue screen X blue screen X blue screen X blue screen
Hyperv X X X X X X X X

Result with xen 4.6.0-release as L0:

L1\L2 XP_x64 RHEL6U4_x64 WIN7_x64 WIN8_x64
XEN V V V V
KVM V V V V
VMware-Workstation X blue screen X panic X blue screen X blue screen
Hyperv X X X X

Result with xen 4.7-rc4 as L0:

L1\L2 XP_x64 RHEL6U4_x64 WIN7_x64 WIN8_x64 WIN8.1_x64
XEN V V V V V
KVM V V V V V
VMware-Workstation X blue screen X panic X blue screen X blue screen X blue screen
Hyperv X X X X X

Result with xen 4.8-rc2 as L0:

L1\L2 RHEL7U2_x64 WIN7_x64 WIN8_x64 WIN8.1_x64
XEN V X X X
KVM X X X X
VMware-Workstation X panic X X X
Hyperv X X X X

Result with xen 4.9.0 as L0:

L1\L2 RHEL7U3_x64 WIN7_x64 WIN8_x64 WIN8.1_x64
XEN X X X X
KVM X X X X
VMware-Workstation X panic X X X
Hyperv X X X X

Result with xen 4.10.0 as L0:

L1\L2 RHEL7U4_x64 WIN7_x64 WIN8_x64 WIN8.1_x64
XEN X X X X
KVM X N/A X X
VMware-Workstation X panic X X X
Hyperv X X X X

Result with xen 4.11-rc5 as L0:

L1\L2 RHEL7U5_x64 WIN7_x64 WIN8_x64 WIN8.1_x64
XEN X X X blue screen X blue screen
KVM X N/A X X
VMware-Workstation X panic X X X
Hyperv X X X X

Know Issues

1. Only L2 EPT/Shadow on L1 EPT is working. L2 EPT/Shadow on L1 Shadow is not supported.
2. Virtual Box fails to boot on top of Xen (L1 panic while booting L2)
3. Hyper-v screen flush issue:
Current the screen flush is not correct after booting hyper-v. Two workarouds:
using remote desktop to connect guest
or set full update mode in Qemu.
4. Using populate-on-demand (memory!=maxmem) or guest paging in an L1 hypervisor for an L2 guest may deadlock the L0 hypervisor.
Icon Ambox.png This means an L1 admin can DOS the L0 hypervisor. This is a potential security issue; for this reason, we do not recommend running nested virtualization in production yet.


Not Tested

1. L1 stress test, performance test
2. L2 stress test performance test
3. L1 save restore, live migration
4. L2 save restore, live migration

Reference Documents

1. Nested Virtualization on Xen http://www-archive.xenproject.org/files/xensummit_intel09/xensummit-nested-virt.pdf
2. Nested Virtualization Update from Intel http://www.slideshare.net/xen_com_mgr/nested-virtualization-update-from-intel
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