Re: [Xen-devel] Can xen support nommu cpu virtualization?

[Ian Campbell <Ian.Campbell@xxxxxxxxxx>]

On Tue, 2012-08-14 at 14:23 +0100, Lei Wen wrote:
> Hi Ian,
> 
> On Tue, Aug 14, 2012 at 9:06 PM, Ian Campbell <Ian.Campbell@xxxxxxxxxx> wrote:
> > On Tue, 2012-08-14 at 10:31 +0100, Lei Wen wrote:
> >> Hi,
> >>
> >> I am a newbie for the XEN area and curious to know whether current XEN
> >> could support nommu arch, or only MPU?
> >> If current it doesn't support, does XEN have any plan or road map to
> >> add this support in future?
> >
> > You should be able to run a NOMMU guest OS as an HVM guest today (or at
> > least I can't think why it wouldn't work).
> >
> > There are no plans to make Xen itself usable on a no-MMU system, use of
> > the MMU is pretty firmly baked into Xens architecture.
> 
> Yep, I get your point. However, on modern embedded system, there are still
> place for no-mmu arches, like the ARM cortex-r7 processor:
> http://www.arm.com/products/processors/cortex-r/cortex-r7.php

OK, you should have made it clear you were talking about ARM.

The ARM port which I am involved with[0] requires the virtualisation
extensions, which AFAIK are a ARMv7-A only and an MMU is always assumed
(it's presence pretty much baked into the extensions in various ways).
We have no plans to support non-mmu ports of this variant of Xen.

The other ARM port (the PV port[1]) does not require virtualisation
extensions, however the correct list for questions/discussion about that
port is the xen-arm@ list.

[0] http://wiki.xen.org/wiki/Xen_ARMv7_with_Virtualization_Extensions
[1] http://wiki.xen.org/wiki/Xen_ARM_%28PV%29

> So making such platform virtualised would have the business benefit, since
> could reduce total embedded product BOM price.
> 
> Do you have any guideline or idea that could make nommu possible? :)

Even the ARM PV port makes extensive use of the MMU to provide isolation
between guests (at least I presume so). If you want to work on nommu
systems then it seems like this would be the first problem you would
have to consider.

Ian.



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