Re: ARM: KVM/XEN: how should we support virt-what?

[Stefano Stabellini <stefano.stabellini@eu.citrix.com>]

On Thu, 26 Mar 2015, Andrew Jones wrote:
> On Wed, Mar 25, 2015 at 10:44:42AM +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. ??.
> > 
> > Thanks,
> > drew 
> > 
> > [1] http://people.redhat.com/~rjones/virt-what/
> > [2] http://git.annexia.org/?p=virt-what.git;a=summary
> > [3] http://git.annexia.org/?p=virt-what.git;a=blob_plain;f=virt-what-cpuid-helper.c;hb=HEAD
> 
> Thanks everyone for their responses. So, the current summary seems to
> be;
> 1) Xen has both a DT node and an ACPI table, virt-what can learn how
>    to probe those.
> 2) We don't have anything yet for KVM, and we're reluctant to create a
>    specific DT node. Anyway, we'd still need to address ACPI booted
>    guests some other way.
> 
> For a short-term, DT-only, approach we could go with a heuristic, one
> that includes Marc's "if hypervisor node exists, then xen, else kvm"
> condition.
> 
> How about SMBIOS for a long-term solution that works for both DT and
> ACPI? We're not populating SMBIOS for arm guests yet in qemu, but now
> that AAVMF has fw_cfg, we should be able to. On x86 we already have
> smbios populated from qemu, although not in a way that allows us to
> determine kvm vs. xen vs. tcg.

I don't think that SMBIOS works with DT.


> Any other suggestions?
> 
> drew
>