FAQ
All - I am running a virtual windows 7 (pro 64) on centos 5.5 x86_64.
I was hoping to run virtual XP inside windows7 in this configuration.

I get an error about cannot start virtual XP when I try this.
Do I not have something setup correctly or can I not run a "double"
virtual environment?

Thanks,

Jerry

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  • Jim Wildman at Jan 4, 2011 at 7:43 pm

    On Tue, 4 Jan 2011, Jerry Geis wrote:

    All - I am running a virtual windows 7 (pro 64) on centos 5.5 x86_64.
    I was hoping to run virtual XP inside windows7 in this configuration.

    I get an error about cannot start virtual XP when I try this.
    Do I not have something setup correctly or can I not run a "double"
    virtual environment?
    I'd be very surprised if that would work. The virtual environments
    check for the correct processor type. A "virtual cpu" is probably not
    on the list..

    ----------------------------------------------------------------------
    Jim Wildman, CISSP, RHCE jim at rossberry.com http://www.rossberry.com
    "Society in every state is a blessing, but Government, even in its best
    state, is a necessary evil; in its worst state, an intolerable one."
    Thomas Paine
  • Arun Khan at Jan 5, 2011 at 7:28 am

    On Wed, Jan 5, 2011 at 6:13 AM, Jim Wildman wrote:
    On Tue, 4 Jan 2011, Jerry Geis wrote:

    All - ?I am running a virtual windows 7 (pro 64) on centos 5.5 x86_64.
    I was hoping to run virtual XP inside windows7 in this configuration.

    I get an error about cannot start virtual XP when I try this.
    Do I not have something setup correctly or can I not run a "double"
    virtual environment?
    I'd be very surprised if that would work. ?The virtual environments
    check for the correct processor type. ?A "virtual cpu" is probably not
    on the list..
    I have not tried a VM within a VM (nested) although I have heard that
    it is possible.

    I guess the correct processor type could be passed with the "-cpu " parameter.

    -- Arun Khan
  • Mitch Patenaude at Jan 5, 2011 at 2:38 pm

    On Tue, 4 Jan 2011, Jerry Geis wrote:
    All - ?I am running a virtual windows 7 (pro 64) on centos 5.5 x86_64.
    I was hoping to run virtual XP inside windows7 in this configuration.

    I get an error about cannot start virtual XP when I try this.
    Do I not have something setup correctly or can I not run a "double"
    virtual environment?
    In general, it is not possible to nest virtualization environments.
    The hypervisor needs to trap certain events/interrupts and reserve
    certain instructions to manage the guest OS. As such, those are not
    available to the guest OS, therefore it cannot be a hypervisor itself.

    You *might* be able to run an emulator (bochs, qemu, etc) within the
    guest OS, but the performance would be something close to abominable.
    I'd say you're better off running two guests, one of Win7 and one of
    WinXP, and use some other mechanism (virtual network) to let them
    communicate.

    -- Mitch
  • Mark Roth at Jan 5, 2011 at 2:49 pm

    Mitch Patenaude wrote:
    On Tue, 4 Jan 2011, Jerry Geis wrote:
    All - ?I am running a virtual windows 7 (pro 64) on centos 5.5
    x86_64.
    I was hoping to run virtual XP inside windows7 in this configuration.

    I get an error about cannot start virtual XP when I try this.
    Do I not have something setup correctly or can I not run a "double"
    virtual environment?
    In general, it is not possible to nest virtualization environments.
    <snip>
    I'd add that all you need to do, if you could get this working, is to open
    a command window, and you'd have *exactly* the same performance as if you
    were running the original PC, on an 8088 with the o/s loaded from floppy
    drives....

    mark
  • Jerry Geis at Jan 5, 2011 at 8:08 am

    I have not tried a VM within a VM (nested) although I have heard that
    it is possible.

    I guess the correct processor type could be passed with the "-cpu " parameter.

    -- Arun Khan
    I have tried "-cpu phenum" which does not run at all.
    and I tried "-cpu core2duo" which runs the guest but does not run the VM
    within a VM.

    Thanks,

    Jerry
  • Flaherty, Patrick at Jan 5, 2011 at 12:24 pm
    From what I remember "-cpu" is to tell the vm what cpu extensions are
    available. I always just use "-cpu host" which has kvm pass in all the
    cpu extensions that the host processor has.

    Using WindowsXP mode on a windows 7 VM sounds dirty. XP mode used to
    require virtualization hardware, now it doesn't. Perhaps passing in a
    cpu that doesn't have virtualization extensions is the way to make
    windows go the non-hardware route. I would expect the performance to be
    abysmal, but it would be a neat trick.

    Patrick

    -----Original Message-----
    From: centos-bounces at centos.org [mailto:centos-bounces at centos.org] On
    Behalf Of Jerry Geis
    Sent: Wednesday, January 05, 2011 8:09 AM
    To: CentOS ML
    Subject: Re: [CentOS] using kvm
    I have not tried a VM within a VM (nested) although I have heard
    that
    it is possible.

    I guess the correct processor type could be passed with the "-cpu "
    parameter.
    -- Arun Khan
    I have tried "-cpu phenum" which does not run at all.
    and I tried "-cpu core2duo" which runs the guest but does not run the
    VM
    within a VM.

    Thanks,

    Jerry

    _______________________________________________
    CentOS mailing list
    CentOS at centos.org
    http://lists.centos.org/mailman/listinfo/centos
  • Kwan Lowe at Jan 5, 2011 at 8:26 am

    On Tue, Jan 4, 2011 at 2:01 PM, Jerry Geis wrote:
    All - ?I am running a virtual windows 7 (pro 64) on centos 5.5 x86_64.
    I was hoping to run virtual XP inside windows7 in this configuration.

    I get an error about cannot start virtual XP when I try this.
    Do I not have something setup correctly or can I not run a "double"
    virtual environment?
    I don't have an answer to your question, but curious as to how the
    virtual XP is running inside Win7. Does it use an entire
    virtualization layer or is it something similar to Wine's approach?

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