Re: [PATCH V2 RFC] fixup! virtio: convert to use DMA api

[Paolo Bonzini]

On 28/04/2016 17:37, Michael S. Tsirkin wrote:
> > All the internally-emulated devices *can* be either translated or
> > untranslated. That's just a matter of software. Surely, you currently
> > *can't* have translated assigned devices (until someone implements the
> > whole VT-d page table shadowing or whatever), so you'll be barred from
> > assigning a device to a slot which *previously* had an untranslated
> > device. But so what? Put it in a different slot instead.
> 
> Unfortunately people got used to be able to put any device
> in any slot, and built external tools around that ability.
> It's rather painful to break this assumption.

Once you move to PCIe, a lot of things become more complicated.  This is
just one of them; instead of needing half a dozen PCI bridges, you'll
need half a dozen plus one.

Paolo