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

[Ard Biesheuvel]

On 26 March 2015 at 19:45, Stefano Stabellini
<stefano.stabellini at eu.citrix.com> wrote:
> 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.
>

SMBIOS works fine with DT