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
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