[libvirt-users] PCI-Passthrough suddenly stopped working
Rouven Sacha
rs at blinkenlichten.de
Thu Jul 12 07:55:09 UTC 2012
Am 12.07.2012 00:38, schrieb Eric Blake:
> 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.
Hi Eric,
thanks for the info.
Reading https://bugzilla.redhat.com/show_bug.cgi?id=715555 , it seems
that 5.8 shouldn't be affected since the kvm on that version doesn't
support interrupt remapping, if I understand correctly. Additionally, if
I run the script provided in the issue description, the check passes
with "Interrupt remapping support available" and the error message
differs: I don't get "Operation not permitted" but "Invalid argument".
I also can't set provides switch in
/sys/module/kvm/parameters/allow_unsafe_assigned_interrupts, since the
file isn't there on my box.
Are there any other circumstances where pci passthrough could fail?
Googling for the error message i get, I can't seem to find any case that
matches mine. This makes me guess that I'd rather accidentally
introduced a misconfiguration than encountered a qemu-kvm/libvirt bug. I
have attached the configuration file of that machine, maybe someone
could have a look at the hostdev section?
Unfortunately, i am currently not able to switch back to the prior
kernel, since the system is in production right now - I will test that
later during the day.
Thanks & cheers,
Rouven
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