[Xen-users] Re: PCI passthrough of cciss HBA

[Christian Tramnitz <chris.ace@xxxxxxx>]

Matthias Reif wrote:
> All,
>
> 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
> grub.conf:
>
> 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?
> Thanks
> Matthias

Using the pciback kernel or module option is not the only way to have 
pciback seize a device. You could use calls to the sysfs structure to 
unbind the device from the cciss driver and then assign it to pciback.
Something along those lines might work after loading pciback:

echo -n '0000:10:00.0' > /sys/bus/pci/drivers/cciss/unbind
echo -n '0000:10:00.0' > /sys/bus/pci/drivers/pciback/new_slot
echo -n '0000:10:00.0' > /sys/bus/pci/drivers/pciback/bind

Make sure you are not using any of the resources (i.e. exclude this is 
vgscan or automounts) to avoid unexpected results...

Best regards,
  Christian


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