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

[Ard Biesheuvel]

On 26 March 2015 at 19:49, Ard Biesheuvel <ard.biesheuvel at linaro.org> wrote:
> 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

... but it needs UEFI ...