Enabling Virtual Machine support

[Jerry Feldman]

On 09/27/2009 07:36 PM, Michael ODonnell wrote:
> Not certain I understand what you're saying but processors in this family
> come out of their power-on Reset state in their simplest, least capable
> mode - interrupts disabled, MMU disabled, 20bit Real Mode addressing,
> etc - and each increase in capability requires a deliberate action on the
> part of the system code (typically the BIOS at first, then later the OS).
>
> Virtual Machine mode is like Virtual 8086 mode in that it's a capability
> that must be explicitly enabled once the OS has rigged itself to manage
> it; this as opposed to somehow being a permanent, static feature of the
> platform or CPU.  And also, AFAIK, no external HW support is required
> of the platform for VM capabilities to be utilized - if the OS is coded
> to support it and the CPU provides it, that's all you (should!)  need.
>
>   
1. Most systems disable the VT extensions in the BIOS by default (AMD
and Intel)> I have an AMD quad core Opteron with VMX, with a Tyan mother
board. The VMX bit shoed up in the processor flags (/proc/cpuinfo), but
I found it was disabled in the BIOS until I manually turned it on.

2. Under Linux your choices for VMMs (Virtual Machine Managers) are
basically KVM/QEMU, QEMU(software), Xen, Virtualbox, and VMWare. Xen and
KVM do use the virtualization hardware.  So far, I don't see any need
for virtualization hardware for Virtualbox or the free versions of
VMWare. If you are using virtualization on a server, more homework is
needed because, in general, performance is more critical. I'm not sure
if Virtualbox supports 64-bit guests, but KVM/QEMU and VMWare certainly
do. Both KVM, QEMU, and Virtualbox are released via the GPL license. I'm
not sure about Xen since Citrix bought it, but you need a Xen-enabled
kernel to run Xen. The KVM modules are bundled with all the recent 2.6
kernels. The Virtualbox modules generally keep up, but I have had a
kernel update where the VBox module was not updated, but that usually
required a quick yum or apt update.

-- 
Jerry Feldman <gaf at blu.org>
Boston Linux and Unix
PGP key id: 537C5846
PGP Key fingerprint: 3D1B 8377 A3C0 A5F2 ECBB  CA3B 4607 4319 537C 5846


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