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

To: xen-users@xxxxxxxxxxxxxxxxxxx
Subject: Re: [Xen-users] Re: PCI passthrough of cciss HBA
From: Matthias Reif <mattreif@xxxxxxxxxxxxx>
Date: Thu, 1 Oct 2009 07:10:03 +1000
Delivery-date: Wed, 30 Sep 2009 14:12:07 -0700
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xen-users-bounces@xxxxxxxxxxxxxxxxxxx wrote on 30/09/2009 07:05:39 PM:

> 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?
> >
>
>
> 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...
>

Thanks for your suggestion. I tried your approach, but for some reason the unbind command freezes. There is nothing in the logs that indicates why.

Thanks
Matthias



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