Hey,
On Thu, Feb 20, 2014 at 12:01:19PM +1030, Rusty Russell wrote:
> Anthony Liguori <> writes:
> > On Tue, Feb 18, 2014 at 4:26 PM, Rusty Russell <> wrote:
> >> Daniel Kiper <> writes:
> >>> Hi,
> >>>
> >>> Below you could find a summary of work in regards to VIRTIO compatibility with
> >>> different virtualization solutions. It was done mainly from Xen point of view
> >>> but results are quite generic and can be applied to wide spectrum
> >>> of virtualization platforms.
> >>
> >> Hi Daniel,
> >>
> >> Sorry for the delayed response, I was pondering... CC changed
> >> to virtio-dev.
Do not worry. It is not a problem. It is not easy issue.
> >> From a standard POV: It's possible to abstract out the where we use
> >> 'physical address' for 'address handle'. It's also possible to define
> >> this per-platform (ie. Xen-PV vs everyone else). This is sane, since
> >> Xen-PV is a distinct platform from x86.
> >
> > I'll go even further and say that "address handle" doesn't make sense too.
>
> I was trying to come up with a unique term, I wasn't trying to define
> semantics :)
>
> There are three debates here now: (1) what should the standard say, and
Yep.
> (2) how would Linux implement it,
It seems to me that we should think about other common OSes too.
> (3) should we use each platform's PCI IOMMU.
I do not want emulate any hardware. It seems to me that we should think about
something which fits best in VIRTIO environment. DMA API with relevant backends
looks promising but I have also some worries about performance. Additionally,
it is Linux Kernel specific stuff so maybe we should invent something more generic
which will fit well in other guest OSes too.
[...]
> It's a fundamental assumption of virtio that the host can access all of
> guest memory. That's paravert, not a hack.
Why? What if guests would like to limit access to their memory? I think
that it will happen sooner or later. Additionally, I think that your
assumption is not hypervisor agnostic which limits implementation of
VIRTIO spec. At least for Xen your idea will make difficulties and
probably prevent VRITIO implementation.
Daniel
