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Re: [Xen-users] RE: [Xen-devel] sharing PCI devices ....

To: xen-users@xxxxxxxxxxxxxxxxxxx
Subject: Re: [Xen-users] RE: [Xen-devel] sharing PCI devices ....
From: Ernst Bachmann <e.bachmann@xxxxxxxx>
Date: Wed, 7 Sep 2005 16:52:45 +0200
Cc: Himanshu Raj <rhim@xxxxxxxxxxxxx>
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On Wednesday 07 September 2005 15:48, Petersson, Mats wrote:
> > Hi Folks,
> >
> > A question about PCI devices. If we leave security problems
> > aside, is it possible to provide access of a PCI device to 2
> > domains (may include dom 0), i.e. would current xen
> > implementation suffice or a PCI device can only be used
> > exclusively by a domain.
>
> If this is for an arbitrary device, it will not work. For a particular
> device, assuming the device is REALLY TRIVIAL, it may be able to make it
> work.
>
> Particularly, a device that uses interrupts to interact with the driver,
> you would have a potential race condition between different drivers.
>
[long explanation deleted]

If you want to have access to the same piece of hardware in different domains, 
you'll probably have more success with a virtualization method working on a 
higher level than xen (iow, BELOW the driver level)

Linux VServer (and maybe BSD Jails) comes to mind here:

With VServer (www.linux-vserver.org) there's only ONE linux kernel running, 
meaning only ONE driver for the device in question, making all the sharing 
problems disappear.

You'd still have multiple OS instances running below that kernel, sharing the 
device between them then can be done on devicenode level and should pose no 
problem at all.

VServer patches seem to work inside xen (search for a previous list post on 
that matter), so you even might be able to combine the best of both worlds on 
one server.

/Ernst

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