On 09/13/2017 03:54 PM, 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' Right. > > 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. Well, this sounds scary :-) > Cons: Does libvirt interpret QMP error strings? No. > > 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. So this is the downside. Well, I think all that we are left with is option 2 then. Or, we can expose nvdimm=on the domain XML (and enable it by default for any domain that already has a nvdimm device configured). BTW: I ran a migration from no nvdimm qemu to one that had -M nvdimm=on and guest migrated happily. So looks like guest ABI is stable (or at least stable enough not to crash). But since ACPI table is changed I doubt that. Also, I found that hotunplug is not implemented yet? error: internal error: unable to execute QEMU command 'device_del': nvdimm device hot unplug is not supported yet. Michal -- libvir-list mailing list libvir-list@xxxxxxxxxx https://www.redhat.com/mailman/listinfo/libvir-list
