Re: [PATCH v1] pc: Support coldplugging of virtio-pmem-pci devices on all buses

[Pankaj Gupta]

Hi David, Vivek,
s
> >> Hi Vivek,
> >>
> >> you have to declare the maxMemory option. Memory devices like
> >> virtio-pmem-pci reside in RAM like a pc-dimm or a nvdimm. If your
> >> virtio-pmem device will be 4GB, you have to add that to maxMemory.
> >>
> >>   <memory unit='GiB'>64</memory>
> >>   <maxMemory unit='GiB'>68</maxMemory>
> >>   <currentMemory unit='GiB'>64</currentMemory>
> >>
> >> (you might have to add "slots='0'" or "slots='1'" to maxMemory to make
> >> libvirt happy)
> >
> > Ok, tried that.
> >
> > <maxMemory slots='1' unit='KiB'>134217728</maxMemory>
> >
> > And now it complains about.
> >
> > error: unsupported configuration: At least one numa node has to be 
> > configured when enabling memory hotplug
> >
> > So ultimately it seems to be wanting me to somehow enable memory hotplug
> > to be able to use virtio-pmem?
>
> That's a libvirt error message. Maybe I am confused how libvirt maps
> these parameters to QEMU ...
>
> NVDIMMs under libvirt seem to be easy:
>
> https://www.redhat.com/archives/libvir-list/2016-August/msg00055.html
>
> Maybe the issue is that virtio-pmem has not been properly integrated
> into libvirt yet:
>
> https://www.redhat.com/archives/libvir-list/2019-August/msg00007.html
>
> And you attempts to force virtio-pmem in via qemu args does not work
> properly.
>
> Maybe maxMemory in libvirt does not directly map to the QEMU variant to
> define the maximum physical address space reserved also for any memory
> devices (DIMMs, NVDIMMs, virtio-pmem, ...). Any libvirt experts that can
> help?
>
> @Pankaj, did you ever get it to run with libvirt?

I did not run virtio-pmem with libvirt. That requires work at libvirt side.
Created [1] document to run from Qemu command line.

[1] https://github.com/qemu/qemu/blob/master/docs/virtio-pmem.rst