Re: [Qemu-devel] [PATCH V4] net: Forbid dealing with packets when VM is not running

["Michael S. Tsirkin" <mst@redhat.com>]

On Mon, Sep 01, 2014 at 07:40:18PM +0100, Stefan Hajnoczi wrote:
> On Tue, Aug 26, 2014 at 04:06:17PM +0800, zhanghailiang wrote:
> > For all NICs(except virtio-net) emulated by qemu,
> > Such as e1000, rtl8139, pcnet and ne2k_pci,
> > Qemu can still receive packets when VM is not running.
> > 
> > If this happened in *migration's* last PAUSE VM stage, but
> > before the end of the migration, the new receiving packets will possibly dirty
> > parts of RAM which has been cached in *iovec*(will be sent asynchronously) and
> > dirty parts of new RAM which will be missed.
> > This will lead serious network fault in VM.
> > 
> > To avoid this, we forbid receiving packets in generic net code when
> > VM is not running.
> > 
> > Bug reproduction steps:
> > (1) Start a VM which configured at least one NIC
> > (2) In VM, open several Terminal and do *Ping IP -i 0.1*
> > (3) Migrate the VM repeatedly between two Hosts
> > And the *PING* command in VM will very likely fail with message:
> > 'Destination HOST Unreachable', the NIC in VM will stay unavailable unless you
> > run 'service network restart'
> > 
> > Signed-off-by: zhanghailiang <zhang.zhanghailiang@huawei.com>
> > ---
> >  v4:
> > - The action of flush queued packets is unnecessary, remove this.
> >   (Thanks for the help of Jason Wang and Stefan). 
> > 
> >  v3:
> > - change the 'vmstate' to 'vm_running'
> > 
> >  v2:
> > - remove the superfluous check of nc->received_disabled 
> > ---
> > 
> >  net/net.c | 7 +++++++
> >  1 file changed, 7 insertions(+)
> 
> Thanks, applied to my net tree:
> https://github.com/stefanha/qemu/commits/net
> 
> Stefan


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