Re: [Qemu-devel] call flow to hit get_pci_config_device() during live migration

[Chris Friesen]

On 06/09/2017 09:42 AM, Chris Friesen wrote:
> Hi,
>
> I'm investigating an issue seen over a live migration from a modified
> qemu-kvm-ev-2.3.0-31.el7_2.7.1 to a modified qemu-kvm-ev-2.6.0-28.el7_3.9.1.  We
> hit an issue down in get_pci_config_device() that caused the migration to fail.
>
> The qemu logs on the destination are included below.
>
> I'm looking for some guidance on the call flow that leads to this function, and
> the likely causes of the bad config data.  And if anyone can help me decode the
> config data information in the log (cmask/wmask/wlcmask) and the logic of the
> "bad config data" check I'd appreciate it.

I think what I end up with is that byte 0x20 (ie 32) of the PCI config for the 
virtio-blk device is 0 in the data coming over the wire, and 0xC in the local 
copy.  Since cmask is 0xff we need to check all the bits in the byte, and both 
wmask and w1cmask are 0 so the version on the wire and the local version should 
be the same.

Does that seem right?

Chris