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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