Re: [Qemu-devel] Using virtio for inter-VM communication

[Paolo Bonzini]

Il 13/06/2014 08:23, Jan Kiszka ha scritto:
> > > That would preserve zero-copy capabilities (as long as you can work
> > > against the shared mem directly, e.g. doing DMA from a physical NIC or
> > > storage device into it) and keep the hypervisor out of the loop.
> >
> > This seems ill thought out.  How will you program a NIC via the virtio
> > protocol without a hypervisor?  And how will you make it safe?  You'll
> > need an IOMMU.  But if you have an IOMMU you don't need shared memory.
>
> Scenarios behind this are things like driver VMs: You pass through the
> physical hardware to a driver guest that talks to the hardware and
> relays data via one or more virtual channels to other VMs. This confines
> a certain set of security and stability risks to the driver VM.

I think implementing Xen hypercalls in jailhouse for grant table and 
event channels would actually make a lot of sense.  The Xen 
implementation is 2.5kLOC and I think it should be possible to compact 
it noticeably, especially if you limit yourself to 64-bit guests.

It should also be almost enough to run Xen PVH guests as jailhouse 
partitions.

If later Xen starts to support virtio, you will get that for free.

Paolo