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[Xen-users] PCI passthrough of cciss HBA

To: <xen-users@xxxxxxxxxxxxxxxxxxx>
Subject: [Xen-users] PCI passthrough of cciss HBA
From: Matthias Reif <mattreif@xxxxxxxxxxxxx>
Date: Wed, 30 Sep 2009 11:30:05 +1000
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I would like to run the following issue past the list to confirm that my problem analysis makes sense or whether I missed something:

We have a HP ML370G6 server with VT-x and VT-d enabled in the BIOS. It is equipped with two Smart Array HBAs - one connected to the HDD array (SmartArray P800) and one connected to an LTO tape drive (SmartArray P212). Both controllers use the same driver on the dom0 (cciss).

dom0 OS = CentOS 5.3 Linux 2.6.18-164.el5xen x86_64
Xen = 3.4.1

My plan was to use PCI passthrough to give a domU unrestricted access to the tape drive. However, I have been unable to get pciback to seize the P212 controller at boot time.

Firstly, I modified the initrd to preload the pciback module:

# mkinitrd -f --preload=pciback /boot/initrd-$(uname -r).img $(uname -r)

Then I added the following lines to modprobe.conf:

options pciback hide=(0000:10:00.0)
install cciss /sbin/modprobe pciback ; /sbin/modprobe --first-time --ignore-install cciss


title CentOS (2.6.18-164.el5xen)
       root (hd0,0)
       kernel /boot/xen.gz-3.4.1 iommu=1
       module /boot/vmlinuz-2.6.18-164.el5xen ro root=LABEL=/
       module /boot/initrd-2.6.18-164.el5xen.img

NB: Passing pciback.hide=(0000:10:00.0) as a kernel parameter does not work:

kernel: Unknown boot option `pciback.hide=(10:00.0)': ignoring

I believe this is because the pciback driver is compiled as a module in the CentOS stock kernel.

After booting with the above config the cciss driver has taken control of PCI device 000:10:00.0 instead of the pciback module.

It seems the pciback module is loaded after the HBA driver (cciss) and therefore does not get a chance to seize the Smart Array P212 controller. This is most likely because the pciback driver is compiled as a module instead of into the kernel. The cciss driver is loaded first to gain access to the hard drive array (via the P800 controller) and to load the pciback module and its configuration. At that point it is too late for pciback to gain control of the Smart Array Controller as the cciss driver has already bound to it.

I belive to fix this I would have to recompile the CentOS kernel with the pciback compiled in statically. Is that correct or is there any other way?


02 6962 7333      Fax: 02 6964 1311

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