Xen project Mailing List

On 5/22/07, Petersson, Mats < Mats.Petersson@xxxxxxx> wrote:

> -----Original Message-----
> From: xen-users-bounces@xxxxxxxxxxxxxxxxxxx
> [mailto:xen-users-bounces@xxxxxxxxxxxxxxxxxxx] On Behalf Of
> Teo En Ming
> Sent: 22 May 2007 14:44
> To: xen-users@xxxxxxxxxxxxxxxxxxx
> Subject: [Xen-users] Firewire, PCI TV Tuner Card, PCI
> Wireless LAN Card, and USB Device Support Under Windows XP Xen Guest
>
> Dear All,
>
> Assuming that I buy a HVM compatible processor and
> motherboard, and having installed a linux host operating
> system with a Xen kernel, I proceed to install a Windows XP
> guest virtual machine. The question is:
>
> Will I be able to use the firewire ports, USB ports, TV Tuner
> program and wireless LAN card inside Windows XP guest VM?

Nope, none of these devices (aside from limited USB support, possibly),
will work under Xen, since (at present) there is no support to
hide/assign PCI devices to the HVM domain. This in turn is because of
the fact that PCI devices access memory directly, which isn't going to
work when Xen has told "lies" [1] to the Windows guest about where the
memory is. So when the guest OS tells the PCI device where in memory
something is, it will not know that this is not the ACTUAL physical
address. And there's no easy way to solve this in software only.

In future generations of processors/chipsets, there will be IOMMU
hardware that allows us to redirect the memory requests from a
particular PCI device, so that we can continue to hide the ACTUAL
physical address and still use the PCI devices within a guest. But
that's a little way out at this time.

[1] All operating systems want memory to start at address zero. Since
only one CAN have this address, guests in HVM-mode will get a fake
memory map that starts at zero and goes to whatever size it's configured
to. The fact that the ACTUAL physical address of the guest's memory is
somewhere else is completely hidden from the guest by using either
shadow-paging or hardware assisted paging (AMD Nested paging or Intel's
corresponding technology) [once this technology reaches customers,
sometime later this year or so].

> Will I be able to do video editing inside Windows XP guest
> VM? Or is networking the one and only feature that is
> supported under Windows XP guest operating system? And I
> won't be able to use anything else inside Windows XP guest?

You should be able to edit video in the guest, as long as you don't rely
on hardware features in PCI devices to do this.

Likewise, I don't see why you need to use Windows to connect to the
Wireless network, you can just as well hide the fact that it's wireless
from Windows, and just use virtual network device, and use the Linux
bridge setting to connect it to the physical Wireless device.

But you are correct, that the current technology only allows a limited
set of hardware features within the guest. This is a hardware
restriction, and it's nothing to do with Xen in itsels, but with the
current state of hardware. Future generations of hardware will remove
some or all of these restrictions (but leaving one remaining
restriction: each guest will HAVE to have it's own hardware to access -
no sharing of a single device without interfacing through a virtual
device - this is because all OS's requires that the hardware they
control is their own. There are hardware devices (such as network cards)
that support "multi-access" by providing multiple device-instances.
These of course can be shared, as they are from a software standpoint
multiple devices, and each device will thus have it's sole owner).

--
Mats
>
> Thank you.
>
>

Re: [Xen-users] Firewire, PCI TV Tuner Card, PCI Wireless LAN Card, and USB Device Support Under Windows XP Xen Guest