[Qemu-devel] Fwd: Direct guest device access from nested guest

[Aaron Fabbri]

Sorry. Resending in plain text.  (Gmail).

---------- Forwarded message ----------

Has anyone considered a paravirt approach?  That is:

Guest kernel:  Write a new IOMMU API back end which does KVM
hypercalls.  Exposes VFIO to guest user processes (nested VMs) as
usual.

Host kernel: KVM does things like collapse {guest_va -> guest_pa ->
host_pa} mappings to {guest_va -> host_pa}, and call through to
underlying IOMMU.

Opinions?



On Wed, Aug 28, 2013 at 12:18 PM, Lluís Vilanova <address@hidden> wrote:
>
> Jan Kiszka writes:
>
> > On 2013-08-28 20:12, Lluís Vilanova wrote:
> >> Jan Kiszka writes:
> >> [...]
> >>>> Is it possible to give a nested guest direct access to a device on the 
> >>>> guest?
> >>>> (more specifically, an AHCI controller).
> >>
> >>> Nope, we are lacking support for emulating or (securely) forwarding
> >>> VT-d/IOMMU features to the first level guest. Would be cool to have,
> >>> just not yet there. But I've talked to Intel people recently, and they
> >>> are considering to support some nested VT-d with KVM.
> >>
> >> Thanks a lot. I've been told there's some patches floating around to add 
> >> such
> >> support, but I suppose they've been long outdated and only work as POCs.
>
> > I haven't seen anything in public.
>
> This is what I've found:
>
>   https://lists.nongnu.org/archive/html/qemu-devel/2011-04/msg01970.html
>
>
> > PS: You have Mail-Followup-To set in your answers - people will drop you
> > from CC this way.
>
> Yes, my mail client tried to be clever but didn't know I'm not subscribed to 
> the
> KVM list :)
>
>
> Lluis
>
> --
>  "And it's much the same thing with knowledge, for whenever you learn
>  something new, the whole world becomes that much richer."
>  -- The Princess of Pure Reason, as told by Norton Juster in The Phantom
>  Tollbooth
>