[Xen-devel] ARM: KVM/XEN: how should we support virt-what?

[Stefano Stabellini]

On Wed, 25 Mar 2015, Ian Campbell wrote:
> On Wed, 2015-03-25 at 10:44 +0100, Andrew Jones wrote:
> > Hello ARM virt maintainers,
> > 
> > I'd like to start a discussion about supporting virt-what[1]. virt-what
> > allows userspace to determine if the system it's running on is running
> > in a guest, and of what type (KVM, Xen, etc.). Despite it being a best
> > effort tool, see the Caveat emptor in [1], it has become quite a useful
> > tool, and is showing up in different places, such as OpenStack. If you
> > look at the code[2], specifically [3], then you'll see how it works on
> > x86, which is to use the dedicated hypervisor cpuid leaves. I'm
> > wondering what equivalent we have, or can develop, for arm.
> > Here are some thoughts;
> > 0) there's already something we can use, and I just need to be told
> >    about it.
> > 1) be as similar as possible to x86 by dedicating some currently
> >    undefined sysreg bits. This would take buy-in from lots of parties,
> >    so is not likely the way to go.
> > 2) create a specific DT node that will get exposed through sysfs, or
> >    somewhere.
> > 3) same as (2), but just use the nodes currently in mach-virt's DT
> >    as the indication we're a guest. This would just be a heuristic,
> >    i.e. "have virtio mmio" && psci.method == hvc, or something,
> >    and we'd still need a way to know if we're kvm vs. xen vs. ??.
> 
> FWIW Xen has a specific node,
> https://git.kernel.org/cgit/linux/kernel/git/devicetree/devicetree-rebasing.git/tree/Bindings/arm/xen.txt
> 
> Doesn't help you with ACPI systems though. IIRC there will be a Xen
> table of some sort.

This is the Xen specific ACPI table:

http://wiki.xenproject.org/mediawiki/images/c/c4/Xen-environment-table.pdf