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

[Aaron Fabbri]

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 support, but I suppose they've been long outdated and only work as POCs.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

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