[libvirt] QEMU -M nvdimm=on and hotplug
Eric Blake
eblake at redhat.com
Wed Sep 13 14:25:36 UTC 2017
On 09/13/2017 08:54 AM, Stefan Hajnoczi wrote:
> Hi Michal,
> You asked how NVDIMM hotplug should work if the domain was launched
> without -M nvdimm=on. I'm not very familiar with ACPI so this may be
> incorrect.
>
> Hotplug relies on the presence of ACPI tables (SSDT Device=NVDR
> _HID=ACPI0012) added by -M nvdimm=on. The ACPI tables contain the
> interface needed to handle hotplug events.
>
> The device_add command fails with the following message if -M nvdimm=on
> is missing:
>
> nvdimm is not enabled: missing 'nvdimm' in '-M'
>
> I'm not sure if ACPI allows SSDT tables to be dynamically added but in
> any case the current QEMU code doesn't support that.
>
> Options for libvirt:
>
> 1. Rely on QEMU's device_add error.
> Pro: If QEMU behavior ever changes then libvirt will also start
> working without code changes.
> Cons: Does libvirt interpret QMP error strings?
In general, we don't want to parse the human-readable portion of an
error; if management software MUST be able to distinguish between two
different types of errors in order to react differently according to
type, then we have a scenario where we want actual differing error
classes (most errors use the generic class, via error_setg(); but it is
still possible to set other error classes where it makes sense).
>
> 2. Only allow NVDIMM hotplug if the domain was started with -M
> nvdimm=on.
>
> I think QEMU will not add -M nvdimm=on to the "pc" machine type by
> default since it adds the NVDIMM DSM hardware interface that increases
> the security attack surface.
>
> Stefan
--
Eric Blake, Principal Software Engineer
Red Hat, Inc. +1-919-301-3266
Virtualization: qemu.org | libvirt.org
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