Re: [Xen-devel] [PATCH net-next v2 1/2] xen-netback: add a vif-is-connected flag

[Paul Durrant <Paul.Durrant@xxxxxxxxxx>]

> -----Original Message-----
> From: annie li [mailto:annie.li@xxxxxxxxxx]
> Sent: 22 September 2013 03:57
> To: Paul Durrant
> Cc: netdev@xxxxxxxxxxxxxxx; xen-devel@xxxxxxxxxxxxx; Wei Liu; David Vrabel;
> Ian Campbell
> Subject: Re: [Xen-devel] [PATCH net-next v2 1/2] xen-netback: add a vif-is-
> connected flag
> 
> 
> On 2013-9-20 21:57, Paul Durrant wrote:
> > Having applied my patch to separate vif disconnect and free, I ran into a
> > BUG when testing resume from S3 with a Windows frontend because the
> vif task
> > pointer was not cleared by xenvif_disconnect() and so a double call to this
> > function tries to stop the thread twice.
> Or it is better to do more implements in windows netfront? For example,
> when the windows vm hibernates, disconnect the vif as required by
> netback: connect-> closing-> closed.
> 

S3 != hibernation; that is S4. The backend does not go away when the VM goes 
into S3 as the domain remains intact. We do go through the correct 
closing->closed transition on the way down but, because of the way the D3->D0 
code in the frontend needs to be generalized, we attempt a second 
closing->closed transition on the way back up. In the S4 case this ok because 
we have a fresh backend, but in the S3 case we don't and therefore hit the 
double-disconnect issue. The fact the backend BUGs in this case clearly shows a 
vulnerability in the backend and thus that is where the fix needs to be made; 
the frontend is doing nothing wrong.

  Paul

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