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

["Christopher Isip" <cmisip@xxxxxxxxx>]

On Mon, May 19, 2008 at 5:40 PM, Mark Williamson <mark.williamson@xxxxxxxxxxxx> wrote:

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
else.

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,
etc...

* ... 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.

Cheers,
Mark

> 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

--
Push Me Pull You - Distributed SCM tool (http://www.cl.cam.ac.uk/~maw48/pmpu/)

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Make sure your pci card is not only supported in linux, but supported in a xen domU.  I have an e100 ethernet card that works fine in dom0 but could only work in a domU If I use xen 3.2.  Earlier versions caused memory allocation errors.

Also, my domU insisted on assigning eth0 to the first pci device it sees despite the alias in /etc/modprobe so it is best to set the physical nic in domU as eth0.  It took me a while to figure this out.  The domU kept on complaining about "device e100 not available, delaying initialization".

Chris


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