Re: pci passthrough - VF reset at boot is dropping assigned MAC

[David Ahern <dsahern@gmail.com>]

On 04/25/11 10:37, Alex Williamson wrote:
> On Mon, 2011-04-25 at 10:28 -0600, David Ahern wrote:
>> Running qemu-kvm.git as of today (ffce28f, April 18, 2011) the virtual
>> function passed to the VM is losing its assigned mac address. That is,
>> prior to launching qemu-kvm, the following command is run to set the MAC
>> address:
>>
>> ip link set dev eth2 vf 0 mac 02:12:34:56:79:20
>>
>> Yet, when the VM boots the MAC address is random which is what happens
>> when the VF is reset. Looking through the commit logs between 0.13.0 --
>> the version in Fedora 14 -- and latest git I found the following:
>>
>> commit d9488459ff2ab113293586c1c36b1679bb15deee
>> Author: Alex Williamson <alex.williamson@redhat.com>
>> Date:   Thu Mar 17 15:24:31 2011 -0600
>>
>>     device-assignment: Reset device on system reset
>>
>>     On system reset, we currently try to quiesce DMA by clearing the
>>     command register.  This assumes that nothing re-enables bus master
>>     support without first de-programming the device.  Use a bigger
>>     hammer to help the guest not shoot itself by issuing a function
>>     reset via sysfs on each system reset.
>>
>>     Signed-off-by: Alex Williamson <alex.williamson@redhat.com>
>>     Acked-by: Chris Wright <chrisw@redhat.com>
>>     Signed-off-by: Marcelo Tosatti <mtosatti@redhat.com>
>>
>>
>> Is this the cause of the MAC address reset and is this behavior intended?
> 
> Ugh, I hope not, it's certainly not an intended side effect.  Can you
> see if the problem still happens if you revert this patch?  If it does,

I commented out the write() in the reset function and indeed the mac
address was not reset on VM boot.

> we might need more device specific reset functions to save and restore
> that extra bit of state.  I assume this is still the 82576 VF you were
> asking about before?  Thanks,

Yes. I got distracted end of last week. Response to that thread coming soon.

David


> 
> Alex
> 
>