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

[Juan Quintela]

zhanghailiang <address@hidden> 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 <address@hidden>

Reviewed-by: Juan Quintela <address@hidden>

It fixes the "collateral" issue than info migrate after migration has
ended shows a remaining ram != 0.

Thanks, Juan.