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

[Anthony Liguori <aliguori@us.ibm.com>]

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?)
>