netdev - Re: Is fallback vhost_net to qemu for live migrate available？

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Message-ID: <20130903084047.GF14104@zion.uk.xensource.com>
Date:	Tue, 3 Sep 2013 09:40:48 +0100
From:	Wei Liu <wei.liu2@...rix.com>
To:	Qin Chuanyu <qinchuanyu@...wei.com>
CC:	Wei Liu <wei.liu2@...rix.com>,
	Anthony Liguori <anthony@...emonkey.ws>,
	"Michael S. Tsirkin" <mst@...hat.com>, <jasowang@...hat.com>,
	KVM list <kvm@...r.kernel.org>, <netdev@...r.kernel.org>,
	<qianhuibin@...wei.com>,
	"xen-devel@...ts.xen.org" <xen-devel@...ts.xen.org>,
	<wangfuhai@...wei.com>, <likunyun@...wei.com>,
	<liuyongan@...wei.com>, <liuyingdong@...wei.com>
Subject: Re: Is fallback vhost_net to qemu for live migrate available？

On Tue, Sep 03, 2013 at 09:28:11AM +0800, Qin Chuanyu wrote:
> On 2013/9/2 15:57, Wei Liu wrote:
> >On Sat, Aug 31, 2013 at 12:45:11PM +0800, Qin Chuanyu wrote:
> >>On 2013/8/30 0:08, Anthony Liguori wrote:
> >>>Hi Qin,
> >>
> >>>>By change the memory copy and notify mechanism ，currently virtio-net with
> >>>>vhost_net could run on Xen with good performance。
> >>>
> >>>I think the key in doing this would be to implement a property
> >>>ioeventfd and irqfd interface in the driver domain kernel.  Just
> >>>hacking vhost_net with Xen specific knowledge would be pretty nasty
> >>>IMHO.
> >>>
> >>Yes, I add a kernel module which persist virtio-net pio_addr and
> >>msix address as what kvm module did. Guest wake up vhost thread by
> >>adding a hook func in evtchn_interrupt.
> >>
> >>>Did you modify the front end driver to do grant table mapping or is
> >>>this all being done by mapping the domain's memory?
> >>>
> >>There is nothing changed in front end driver. Currently I use
> >>alloc_vm_area to get address space， and map the domain's memory as
> >>what what qemu did.
> >>
> >
> >You mean you're using xc_map_foreign_range and friends in the backend to
> >map guest memory? That's not very desirable as it violates Xen's
> >security model. It would not be too hard to pass grant references
> >instead of guest physical memory address IMHO.
> >
> In fact, I did what virtio-net have done in Qemu. I think security
> is a pseudo question because Dom0 is under control.
> 

Consider that you might have driver domains. Not every domain is under
control or trusted. Also consider that security model like XSM can be
used to audit operations to enhance security so your foreign mapping
approach might not always work.

In short term foreign mapping can save you some time implementing the
prototype. In long term using grant table is the proper way to go. And
IMHO the benifit outweights the cost.

Wei.

> Host could access memory of guest in KVM much easier than Xen,
> but I hadn't heard someone said KVM is un-secret.
> 
> Regards
> Qin chuanyu
> 
> 
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