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

To: Christian Tramnitz <chris.ace@xxxxxxx>
Subject: Re: [Xen-users] Re: About NIC passthrough to the guest system
From: Paul Schulze <avlex@xxxxxxx>
Date: Mon, 27 Apr 2009 13:49:35 +0200
Cc: xen-users@xxxxxxxxxxxxxxxxxxx
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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 Christmas?
Because OCT31 = DEC25.

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