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

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Date:	Mon, 23 Sep 2013 08:51:23 +0000
From:	Paul Durrant <Paul.Durrant@...rix.com>
To:	annie li <annie.li@...cle.com>
CC:	"netdev@...r.kernel.org" <netdev@...r.kernel.org>,
	"xen-devel@...ts.xen.org" <xen-devel@...ts.xen.org>,
	Wei Liu <wei.liu2@...rix.com>,
	David Vrabel <david.vrabel@...rix.com>,
	Ian Campbell <Ian.Campbell@...rix.com>
Subject: RE: [Xen-devel] [PATCH net-next v2 1/2] xen-netback: add a
 vif-is-connected flag

> -----Original Message-----
> From: annie li [mailto:annie.li@...cle.com]
> Sent: 22 September 2013 03:57
> To: Paul Durrant
> Cc: netdev@...r.kernel.org; xen-devel@...ts.xen.org; 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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