libvirt users - Jul 2012 - PCI-Passthrough suddenly stopped working

Hi everybody!

On a Centos 5.8 with libvirt qemu-0.10.5-1.el5.2, libvirt-0.8.2-22.el5 and
2.6.18-308.11.1.el5 I have a Windows machine that used to have pci-passthrough
for a device enabled and working.

After an update (kernel, libvirt afaik) and  a reboot, pci-passthrough stopped
working. Intel IOMMU is enabled (can see that from the dmesg output). All i get
on the console when i try to start the vm is the following:

Fehler: internal error process exited while connecting to monitor: char device
redirected to /dev/pts/3
Failed to assign device "14:00.2" : Invalid argument
Failed to deassign device "14:00.2" : Invalid argument
Failed to initialize assigned device host=14:00.2

SELinux ist disabled.

Does anyone have any hint what could have possibly gone wrong?

As an additional info: "virsh nodeddev-list" also doesn't work. I
don't know if I mix that up, but i seem to remember that that used to work
on that machine.

root at kvm ~]# virsh nodedev-list --tree
Fehler: Failed to count node devices
Fehler: this function is not supported by the connection driver:
virNodeNumOfDevices

Any hints are greatly appreciated!

Thanks & Cheers,

Rouven

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On 07/11/2012 04:24 PM, Rouven Sacha wrote:
> Hi everybody!
> 
> On a Centos 5.8 with libvirt qemu-0.10.5-1.el5.2, libvirt-0.8.2-22.el5
> and 2.6.18-308.11.1.el5 I have a Windows machine that used to have
> pci-passthrough for a device enabled and working.
> 
> After an update (kernel, libvirt afaik) and  a reboot, pci-passthrough
> stopped working. Intel IOMMU is enabled (can see that from the dmesg
> output).
This may be the result of a security fix in the new kernel.  I know at
least one older version of Intel chips has a bug where IOMMU can be
exploited by a guest to take control over the host, so on those chips,
newer kernels now require to explicitly enable a kernel module parameter
to state that you are going to allow passthrough to the guest in spite
of the security risk.  That is, you may need to use:

modprobe kvm allow_unsafe_assigned_interrupts=1

with your newer kernel.  Unfortunately, I wasn't able to find a better
URL to a page documenting this issue, so that implies we probably also
need a patch to the libvirt documentation with regards to using device
passthrough.

-- 
Eric Blake   eblake at redhat.com    +1-919-301-3266
Libvirt virtualization library http://libvirt.org



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