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Re: [Xen-users] Simple Query on PCI passthrough I/O

On Monday 19 May 2008, Joseph L. Casale wrote:
> You only need a nic that your DomU supports (or can with a new module).
> since you hide it and pass it through in Dom0, it doesn't even see it...

Indeed.  In principle pretty much any PCI device ought to be possible to pass 
through to a guest.  As long as the guest can support that network card then 
it should work OK.

There are a few PCI devices that have caused people trouble when doing 
passthrough (searching the mailing list archives on xen-devel and xen-users 
may reveal some of these) sometimes due to odd hardware behaviour, sometimes 
due to driver bugs.  In general there's not a hard-and-fast rule other than 
observing other's experience.  Plenty of people seem to be happily using this 
feature, though.

I'd suggest you try a NIC (maybe just try with the current NIC in your host, 
initially) and see if you can make it work.  I'd guess that you have a pretty 
high chance of it working once you've got the setup right.  You could then 
chose to buy another of the known-good card in your host, or try something 

Other things to be aware of:

* Passing a PCI device to a guest makes that guest as trusted as dom0.  It's 
just as powerful in terms of being able to snoop data, crash the system, 

* ... unless you are using VT-d, in which case you can pass the PCI device to 
an HVM guest without that guest being able to stomp all over memory.  Patches 
to support this for PV guests are in development but not done yet.

* Don't try to xm pause, save or suspend the guest with the PCI card!  Bad 
things may well happen ;-)

* You need to be running a dom0 kernel in the guest with the PCI card.


> jlc
> From: xen-users-bounces@xxxxxxxxxxxxxxxxxxx
> [mailto:xen-users-bounces@xxxxxxxxxxxxxxxxxxx] On Behalf Of Asim Sent:
> Monday, May 19, 2008 12:51 PM
> To: xen-users@xxxxxxxxxxxxxxxxxxx
> Subject: [Xen-users] Simple Query on PCI passthrough I/O
> Hi,
> I want to perform pass through I/O from my domU. I guess I would need an
> additional network card for the same. Is there any preference on the second
> network card I should get or any one is fine? I have a x86_64 machine with
> Cent OS 4.4 running. Are there any additional considerations that I cannot
> see - Kindly let me know.
> Thanks,
> Asim

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