[libvirt] PF interface brought down if guest using a VF in hostdev mode under 802.1Qbh

[Nishank Trivedi (nistrive)]

Hi,

In 802.1Qbh case where exists a SR-IOV capable network device, if any of
the virtual functions of this device is used in hostdev mode for the
guest, port-profile disassociate will also cause physical function
interface to go down. This appears to be a bug, but wanted to find if this
was done intentionally for some reasons.

To be more specific, if a network device supports SRIOV and its VF is
being used in pci passthrough mode, when the guest is shutdown or
destroyed following happens -

qemuProcessStop
\_ qemuDomainReAttachHostdevDevices(hostdevs)
 \_ qemuDomainHostdevNetConfigRestore(hostdev)
  \_ virNetDevPortProfileDisassociate(linkdev)
   \_ virNetDevSetOnline(linkdev, false)

In above, qemuDomainHostdevNetConfigRestore() finds out the PF for
provided hostdev (which is VF) and passes it to
virNetDevPortProfileDisassociate() as linkdev. Later, linkdev gets passed
to virNetDevSetOnline() where the interface is brought down by clearing
IFF_UP flag. 

However, in macvtap emulation mode,
virNetDevMacVLanDeleteWithVPortProfile() passes VF as linkdev (and -1 as
vf) to virNetDevPortProfileDisassociate(), hence, not affecting PF at all.

Bringing down a PF, when only VF is being brought down is not expected
behavior (unless, I'm missing something here). A way to get around it
would be to check if there exists vf (>=0) in
virNetDevPortProfileDisassociate(), and if so, it should only pass the
interface name of this VF rather than PF itself to virNetDevSetOnline().
If it sounds reasonable, I'll send out a fix.

Thanks,
Nishank


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Re: [libvirt] PF interface brought down if guest using a VF in hostdev mode under 802.1Qbh

[Nishank Trivedi (nistrive)]

On 8/7/12 8:15 PM, "Laine Stump"  wrote:

>
>Yes, I believe you are correct that virNetDevSetOnline is being called
>with the wrong device name (I could be wrong though - is there maybe
>some odd rule that the PF must be UP before the VFs will be up?

PF should be UP prior to VF only if there is some proxy'ing or some
control data being sent by PF on behalf of VF. Same could be true for
bringing VF down. 

>In case
>case, we certainly shouldn't be setting the PF to IFF_DOWN). But in the
>case of PCI passthrough, does it even need to be called at all?

Not for PF for sure. While VF is getting disassociated with port profile,
VF interface still needs to be brought down. So virNetDevSetOnline should
be passed VF interface, if vf >= 0.

>
>Cc'ing Roopa in case she missed this in all the other traffic.

Invalid email id, cc'ing Christian instead.

Thanks,
Nishank


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Re: [libvirt] [PATCH] Fix issue of PF brought down if VF is 8021.Qbh and pci passthrough

[Nishank Trivedi (nistrive)]

On 8/30/12 12:21 PM, "Stefan Berger"  wrote:

>
>ACK -- will fix the tab with spaces, add you to the list of authors and
>push the patch

Thanks Stephan.


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