Re: [kvm-devel] [PATCH 3/3] virtio PCI device

Anthony Liguori
2007-11-08T15:06:20Z

Avi Kivity wrote:
> If a pci device is capable of dma (or issuing interrupts), it will be
> useless with pv pci.

Hrm, I think we may be talking about different things. Are you thinking
that the driver I posted allows you to do PCI pass-through over virtio?
That's not what it is.

The driver I posted is a virtio implementation that uses a PCI device.
This lets you use virtio-blk and virtio-net under KVM. The alternative
to this virtio PCI device would be a virtio transport built with
hypercalls like lguest has. I choose a PCI device because it ensured
that each virtio device showed up like a normal PCI device.

Am I misunderstanding what you're asking about?

Regards,

Anthony Liguori

>
>>> I think that with Amit's pvdma patches you
>>> can support dma-capable devices as well without too much fuss.
>>>
>>
>> What is the use case you're thinking of? A semi-paravirt driver that
>> does dma directly to a device?
>
> No, an unmodified driver that, by using clever tricks with dma_ops,
> can do dma directly to guest memory. See Amit's patches.
>
> In fact, why do a virtio transport at all? It can be done either with
> trap'n'emulate, or by directly mapping the device mmio space into the
> guest.
>
>
> (what use case are you considering? devices without interrupts and
> dma? pci door stoppers?)
>