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Re: [Xen-users] Re: About NIC passthrough to the guest system

To: "Paul Schulze" <avlex@xxxxxxx>, "Christian Tramnitz" <chris.ace@xxxxxxx>
Subject: Re: [Xen-users] Re: About NIC passthrough to the guest system
From: "Alex Chan" <alex.chan@xxxxxxxxxxx>
Date: Tue, 28 Apr 2009 15:17:05 +0800
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Hi Christian and Paul,

        I try to see the IRQ, /proc/interrupts , there is no IRQ that
(0a:00.1) is using. So is that mean the post is hide in the host so cannot
see the IRQ?
Also I see some web page that they add

"install xxxx /sbin/modprobe pciback ;
/sbin/modprobe --first-time --ignore-install xxxx"

in the /etc/modprobe.conf, is that need to do that ?

Also when I add "pciback.hide=(0a:00.1)" in the command line of grub.conf,
it says "Unknown boot option pciback.hide". So I cannot add it in the

I am wondering is that I miss some config for the PCI passthrough ?

Thank you so much.

Best Regards

----- Original Message ----- 
From: "Paul Schulze" <avlex@xxxxxxx>
To: "Christian Tramnitz" <chris.ace@xxxxxxx>
Cc: <xen-users@xxxxxxxxxxxxxxxxxxx>
Sent: Monday, April 27, 2009 7:49 PM
Subject: Re: [Xen-users] Re: About NIC passthrough to the guest system

Hash: SHA1

Hi Christian and Alex,

On 27 Apr 2009, at 12:36, Christian Tramnitz wrote:

> When running hvm you need vt-d support to pass-through devices.
> Apart from that I doubt that you will be able to passthrough one
> port of a dual-port nic, you may have to pass-through the whole card.

If the DomU is starting without displaying any error, I think it is
safe to assume, that it is running on hardware with VT-d support,
since in my experience, a HVM DomU does not start at all, if the guest
config sets up a device for PCI passthrough (I could be wrong here,
haven't tried it lately).

That depends on the NICs design. I own a D-Link DFE-580TX (4 ports)
and on that one, each port is more or less stand-alone, not sharing
anything with the other chips on the board. My current setup (2 ports
in Dom0, 2 ports passed through to my IPCop DomU) works just fine with
that. That Intel NIC looks like a similar setup though, so it should
work somehow. However, I am currently running my DomU in PV mode, but
with only a few modifications, Alex should be able to do that too, if
necessary. It is also important to take a good look at the IRQs (lspci
- -v) and keep the sharing of IRQs between all Xen instances to a
minimum. Oh yeah and never pass a device to a DomU that shares an IRQ
with your HDD controller, be it SCSI, SATA or IDE... that can really
lead to "unexpected" results.

> Alex Chan wrote:
> [...]
>>  [root@hm02 xen]# cat /etc/modprobe.conf
>> options pciback hide=(0a:00.1)
>> alias eth0 bnx2
>> alias eth1 bnx2
>> alias eth2 bnx2
>> alias eth3 e1000e
>> alias eth4 e1000e
>> alias eth5 e1000e
>> alias eth6 e1000e
>> alias scsi_hostadapter megaraid_sas
>> alias scsi_hostadapter1 ata_piix
>> alias scsi_hostadapter2 usb-storage
> [...]

And finally, I looked over your config, Alex, and it looks ok, but I
am wondering, why you define pciback.hide in /etc/modprobe.conf
instead of the kernel command-line. Since I assume, the device driver
for your NIC is built as a module, and /etc/modprobe.conf should be
accounted on loading it, this might be correct. But pciback is built
into your kernel anyway so to avoid any doubt on whether it is or not,
I would suggest putting it on the command-line (simply add
pciback.hide=(0a:00.1)). This might not help at all, but at least then
you can be sure that nothing else happens to the PCI device besides
being seized by pciback.

I hope this helps


- --
Paul Schulze
Mail: avlex82@xxxxxxxxx

Why can't a programmer tell the difference between Halloween and
Because OCT31 = DEC25.

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