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Re: [Qemu-devel] How to lock-up your tap-based VM network
From: |
Paul Brook |
Subject: |
Re: [Qemu-devel] How to lock-up your tap-based VM network |
Date: |
Tue, 13 Apr 2010 14:02:24 +0100 |
User-agent: |
KMail/1.12.4 (Linux/2.6.33-2-amd64; KDE/4.3.4; x86_64; ; ) |
> Paul Brook wrote:
> >> But anyway, this flow control mechanism is buggy - what if instead of
> >> an interface down, you just have a *slow* guest? That should not push
> >> back so much that it makes other guests networking with each other
> >> slow down.
> >
> > The OP described multiple guests connected via a host bridge. In this
> > case it is entirely the host's responsibility to arbitrate between
> > multiple guests. If one interface can block the bridge simply by failing
> > to respond in a timely manner then this is a serious bug or
> > misconfiguration of your host bridge.
>
> It's not the bridge, I think it's limited to the tun driver as bridge
> participant and how it is configured/used by QEMU.
If one tap interface can prevent correct operation of another by failing to
read data, then this is clearly a host kernel bug.
I've no idea whether it's a bug in the TAP implementation (e.g. shared queue
between independent devices), a bug in the bridging implementation (drops
unrelated packets when one port is slow), or some interaction between the two,
but it's definitely not a qemu bug.
I'm sure there are plenty of ways to DoS a qemu instance, and prevent it
reading data from its tap interface. How/whether this effects other unrelated
processes on the host machine is not something qemu can or should know about.
Paul
Re: [Qemu-devel] How to lock-up your tap-based VM network, Blue Swirl, 2010/04/13