Re: [Xen-devel] xl/SR-IOV: disposition of VFs when PF disappears?

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> On 27.10.14 at 14:03, <andrew.cooper3@xxxxxxxxxx> wrote:
> On 27/10/14 12:36, Jan Beulich wrote:
>> All,
>>
>> Intel reports that the sequence
>>
>> - xl pci-assignable-add <VF>
>> - briefly run guest using that device [not sure whether that's really a
>>   necessary step]
>> - xl pci-assignable-add <PF of VF>
>>
>> results in both VF and PF being listed as assignable (the fact that as a
>> result the PF handed to a guest doesn't work is secondary here, as I
>> think this is a driver issue). Is that really how it should be? Shouldn't
>> instead all VFs get removed when the PF device (e.g. due to the
>> PF driver getting unloaded, which is a necessary part of making it
>> assignable) goes away? Or is it required for the admin to manually
>> remove the assignable VFs prior to making the PF go away?
> 
> Which type of devices are these?

Intel having reported that, it's Intel NICs (not sure which driver,
but I also don't think this is relevant).

> From my recollection using igb and ixgbe with Netscalar, the VFs are
> created after the PF driver has bound and started up.

Yes, they're being created as the PF driver loads.

> Moving the binding from the real PF driver to pciback should remove the
> VFs, although I would not be surprised if this has been overlooked, or
> is expected to work but currently buggy.

Right - as a side effect of the PF getting unbound from its driver.

> As a logical consequence of the above, a PF with VFs must strictly not
> be assignable, for safety reasons.

I don't think this should be enforced, but rather left to the discretion
of the host admin.

> There are security considerations involved with passing a PF to a
> domain, as that domU can still cause VFs to appear in dom0.  A PF should
> either stay in dom0, be given to a trusted device driver domain.

How would a PF driver in a DomU cause VFs to appear in Dom0?
These aren't being found by scanning the bus, but rather get
created via software means afaik.

Jan


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