[libvirt] QEMU -M nvdimm=on and hotplug

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? 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