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RE: [Xen-users] unmodified guests (VMX?) access PCI devices

To: therion@xxxxxxxxxxxx, xen-users@xxxxxxxxxxxxxxxxxxx
Subject: RE: [Xen-users] unmodified guests (VMX?) access PCI devices
From: "Petersson, Mats" <Mats.Petersson@xxxxxxx>
Date: Mon, 4 Sep 2006 13:33:35 +0200
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Thread-topic: [Xen-users] unmodified guests (VMX?) access PCI devices

> -----Original Message-----
> From: xen-users-bounces@xxxxxxxxxxxxxxxxxxx 
> [mailto:xen-users-bounces@xxxxxxxxxxxxxxxxxxx] On Behalf Of Georg Bege
> Sent: 01 September 2006 19:39
> To: xen-users@xxxxxxxxxxxxxxxxxxx
> Subject: [Xen-users] unmodified guests (VMX?) access PCI devices
> Hash: SHA1
> Hello folks
> I played a lot with Xen last days,
> isnt it possible to access PCI devices which are  hidden
> from dom0?

There's no support currently for this. It's not TERRIBLY difficult to
implement the bit that forwards the PCI device to the HVM domain.

There's a but tho': it's non-trivial to make it work further on, because
drivers will (almost) always pass a physical address to the card. But in
a HVM domain the OS's view of a physical address isn't the Machine
Physical Address but a "virtual physical address" (aka Guest Physical
Address). If your PCI device is anything like a network card, SCSI
controller or graphics card, it will do direct memory accesses from the
card to physical memory, and in the current model, that would require a
machine-physical address, which isn't available to the driver/OS in HVM

I hope this is clear, but feel free to ask for further details if you

> I didnt get it - at least my windows domain didnt get it.
> Another question:
> Im using hvmloader but many pages also talk about the vmxloader,
> was it prior the hvmloader coz it doesnt exist anymore?

Yes, vmxloader used to be the name for hvmloader before HVM was invented
(i.e. at the time when Xen only had VT support and no SVM support). 

> cheers
> - --
> Georg 'Therion' Bege
> http://coruscant.info
> http://www.ninth-art.de
> therion@xxxxxxxxxxxx <therion at ninth minus art dot de>
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