Xen users - Jan 2006 - How do unmodified guests work with Xen?

Hi!

Although I''m tracking Xen (thanks to the Xen team -- they''ve
done a great
job!) and virtualization for a while I still couldn''t figure out how
unmodified guests work with Xen 3.0. Let''s assume I''d like to
install
Windows 2003 on Xen and have a system that has the VT/Pacifica feature.
Since the guest doesn''t have access to the hardware it will need either
(Xen) drivers that know how to perform I/O (e.g., disk, networking) or Xen
needs to emulate hardware. Another problem I see is that Windows wants to
have a graphics card with at least VGA capabilities for installation. At
the moment I cannot see any other way than hardware emulation. Maybe
someone can tell how Xen works with unmodified guests in detail.

Thank you!

Kind regards,

Stephan

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I am also interested in how this process is accomplished. I understand that 
headless
installs of w3k server are possible on equipment that supports EMS but am
confounded by how hardware device driver support is provided in Xen at the
moment for this operating system?

See http://support.microsoft.com/default.aspx?scid=kb;en-us;815273

Any words of wisdom from the enlightened would be most appreciated.

Regards

Petar
----- Original Message ----- 
From: "Stephan Austermühle" <au@hcsd.de>
To: <xen-users@lists.xensource.com>
Sent: Friday, January 20, 2006 4:56 PM
Subject: [Xen-users] How do unmodified guests work with Xen?

> Hi!
>
> Although I''m tracking Xen (thanks to the Xen team --
they''ve done a great
> job!) and virtualization for a while I still couldn''t figure out
how
> unmodified guests work with Xen 3.0. Let''s assume I''d
like to install
> Windows 2003 on Xen and have a system that has the VT/Pacifica feature.
> Since the guest doesn''t have access to the hardware it will need
either
> (Xen) drivers that know how to perform I/O (e.g., disk, networking) or Xen
> needs to emulate hardware. Another problem I see is that Windows wants to
> have a graphics card with at least VGA capabilities for installation. At
> the moment I cannot see any other way than hardware emulation. Maybe
> someone can tell how Xen works with unmodified guests in detail.
>
> Thank you!
>
> Kind regards,
>
> Stephan


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Xen-users mailing list
Xen-users@lists.xensource.com
http://lists.xensource.com/xen-users

Hi!

pjn@nikolich.org schrieb:
> I am also interested in how this process is accomplished. I understand
> that headless
> installs of w3k server are possible on equipment that supports EMS but am
> confounded by how hardware device driver support is provided in Xen at the
> moment for this operating system?
Is there really nobody out there who can tell some technical details?

Kind regards,

Stephan


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Xen-users@lists.xensource.com
http://lists.xensource.com/xen-users

On Wednesday 25 January 2006 07:59, Stephan Austermühle
wrote:
> Hi!
>
> pjn@nikolich.org schrieb:
> > I am also interested in how this process is accomplished. I understand
> > that headless
> > installs of w3k server are possible on equipment that supports EMS but
am
> > confounded by how hardware device driver support is provided in Xen at
> > the moment for this operating system?
>
> Is there really nobody out there who can tell some technical details?
AFAIK it just works like it does in qemu, bochs, vmware, ...
The guest sees an (S)VGA and network device, accesses to that (virtual) device 
are trapped and passed to an hardware emulator.

/Ernst

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> AFAIK it just works like it does in qemu, bochs, vmware, ...
> The guest sees an (S)VGA and network device, accesses to that (virtual)
> device are trapped and passed to an hardware emulator.
Exactly.  In more detail:

The Xen hypervisor itself remains a very small piece of software, and
doesn''t
contain device emulation code (except for a few performance-critical pieces 
of platform hardware).

The guest can mostly run directly on the (VT-enabled) CPU.  Various privileged 
CPU operations need to emulated to make this work properly.  Hardware devices 
can essentially be emulated entirely by trapping guest attempts to access IO 
memory regions, or IO ports and feeding these into a "model" of how
the
device will respond to these accesses.  Currently the device models run as a 
daemon process in dom0 (the actual device emulation code is derived from 
QEmu).  Whenever an attempt to do mmio or port io is trapped by Xen, it 
passes the details up to the device model daemon, which feeds these details 
into the device emulation.  The device emulation simulates the current device 
state and (when necessary) maps the memory of the virtual machine and 
transfers data into it.

Using this process, we''re able to completely emulate real hardware
devices
(network card, block, video, eventually sound too) for the benefit of 
unmodified guests, which still expect to see these features.

The architecture is expected to change to a higher-performance implementation 
during the evolution of Xen''s full virtualisation support.

Does that help everybody?

Cheers,
Mark

-- 
Dave: Just a question. What use is a unicyle with no seat?  And no pedals!
Mark: To answer a question with a question: What use is a skateboard?
Dave: Skateboards have wheels.
Mark: My wheel has a wheel!

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Hi Mark!

Mark Williamson schrieb:
> Does that help everybody?
Yes, thank you very much for the information you provided. Now I know
that there definitely is hardware emulation involved when using
unmodified guests.

Kind regards,

Stephan


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Xen-users@lists.xensource.com
http://lists.xensource.com/xen-users

"A port of Windows XP was developed for an earlier version of Xen, but is 
not available for release due to licence restrictions"

Presumably something close to the Windows standard driver model was used to 
make it work for interfacing to the underlying virtualised hardware. Is this 
support available. Clearly the modified version of XP itself would not be 
but why not the hardware/driver support if it exists?

Of course I could be entirely off-base here but it never hurts to ask :-)

..pjn
----- Original Message ----- 
From: "Mark Williamson" <mark.williamson@cl.cam.ac.uk>
To: <xen-users@lists.xensource.com>
Cc: "Ernst Bachmann" <e.bachmann@xebec.de>; "Stephan
Austermühle"
<au@hcsd.de>; <pjn@nikolich.org>
Sent: Wednesday, January 25, 2006 8:36 PM
Subject: Re: [Xen-users] How do unmodified guests work with Xen?

>> AFAIK it just works like it does in qemu, bochs, vmware, ...
>> The guest sees an (S)VGA and network device, accesses to that (virtual)
>> device are trapped and passed to an hardware emulator.
>
> Exactly.  In more detail:
>
> The Xen hypervisor itself remains a very small piece of software, and 
> doesn''t
> contain device emulation code (except for a few performance-critical 
> pieces
> of platform hardware).
>
> The guest can mostly run directly on the (VT-enabled) CPU.  Various 
> privileged
> CPU operations need to emulated to make this work properly.  Hardware 
> devices
> can essentially be emulated entirely by trapping guest attempts to access 
> IO
> memory regions, or IO ports and feeding these into a "model" of
how the
> device will respond to these accesses.  Currently the device models run as 
> a
> daemon process in dom0 (the actual device emulation code is derived from
> QEmu).  Whenever an attempt to do mmio or port io is trapped by Xen, it
> passes the details up to the device model daemon, which feeds these 
> details
> into the device emulation.  The device emulation simulates the current 
> device
> state and (when necessary) maps the memory of the virtual machine and
> transfers data into it.
>
> Using this process, we''re able to completely emulate real hardware
devices
> (network card, block, video, eventually sound too) for the benefit of
> unmodified guests, which still expect to see these features.
>
> The architecture is expected to change to a higher-performance 
> implementation
> during the evolution of Xen''s full virtualisation support.
>
> Does that help everybody?
>
> Cheers,
> Mark
>
> -- 
> Dave: Just a question. What use is a unicyle with no seat?  And no pedals!
> Mark: To answer a question with a question: What use is a skateboard?
> Dave: Skateboards have wheels.
> Mark: My wheel has a wheel!
>
> _______________________________________________
> Xen-users mailing list
> Xen-users@lists.xensource.com
> http://lists.xensource.com/xen-users
>
> 


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