RE: [Xen-devel] HVM guest sees two NICs even though just one vif configured

[Stefano Stabellini <stefano.stabellini@xxxxxxxxxxxxx>]

On Thu, 6 Aug 2009, Fischer, Anna wrote:
> > Subject: Re: [Xen-devel] HVM guest sees two NICs even though just one
> > vif configured
> > 
> > On 06/08/2009 10:32, "Fischer, Anna" <anna.fischer@xxxxxx> wrote:
> > 
> > > For me this does not sound right. If I configure my guest with only a
> > single
> > > NIC in the configuration file, then there should not be any way for
> > the guest
> > > to set up and use two NICs at the same time.
> > >
> > > Is this a known issue? How is this supposed to be handled?
> > 
> > I think it's deliberate, to allow install of an OS with emulated
> > driver,
> > followed by switchover to PV drivers, wth no need for config changes.
> 
> I assumed that was the reason behind this. However, a switchover would need 
> to guarantee that a guest cannot use two NICs at the same time, doesn't it? 
> Because otherwise the guest can send out of two separate devices at the same 
> time and it could cause unexpected behaviour unless it is explicitly 
> prevented at the backends in Dom0, e.g. through filtering or anti-spoofing I 
> guess.
> 

I more recent qemu allows the pv drivers in the guest to disconnect the
emulated devices to avoid these problems.


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