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

From: Pankaj Gupta <pankaj.gupta.linux@gmail.com>
To: David Hildenbrand <david@redhat.com>
Cc: "Daniel P. Berrange" <berrange@redhat.com>,
	Eduardo Habkost <ehabkost@redhat.com>,
	"Michael S. Tsirkin" <mst@redhat.com>,
	qemu-devel@nongnu.org, Paolo Bonzini <pbonzini@redhat.com>,
	Igor Mammedov <imammedo@redhat.com>,
	Jiri Denemark <jdenemar@redhat.com>,
	Vivek Goyal <vgoyal@redhat.com>,
	Richard Henderson <rth@twiddle.net>
Subject: Re: [PATCH v1] pc: Support coldplugging of virtio-pmem-pci devices on all buses
Date: Wed, 27 May 2020 21:51:50 +0200	[thread overview]
Message-ID: <CAM9Jb+hxR2Q22YpBcA0-Rv=gbbawVhZLR-Ld7_YT7hn7S9-UsA@mail.gmail.com> (raw)
In-Reply-To: <32210631-5933-088c-52e5-9e9eb2d800e3@redhat.com>

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