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

From: David Hildenbrand <david@redhat.com>
To: Vivek Goyal <vgoyal@redhat.com>
Cc: Pankaj Gupta <pankaj.gupta.linux@gmail.com>,
	Eduardo Habkost <ehabkost@redhat.com>,
	"Michael S. Tsirkin" <mst@redhat.com>,
	qemu-devel@nongnu.org, Igor Mammedov <imammedo@redhat.com>,
	Paolo Bonzini <pbonzini@redhat.com>,
	Richard Henderson <rth@twiddle.net>
Subject: Re: [PATCH v1] pc: Support coldplugging of virtio-pmem-pci devices on all buses
Date: Tue, 26 May 2020 15:44:10 +0200	[thread overview]
Message-ID: <dddadb61-b0af-a9c0-64f8-ac3c47d37566@redhat.com> (raw)
In-Reply-To: <20200526132840.GD108774@redhat.com>

On 26.05.20 15:28, Vivek Goyal wrote:
> On Mon, May 25, 2020 at 10:45:11AM +0200, David Hildenbrand wrote:
>> E.g., with "pc-q35-4.2", trying to coldplug a virtio-pmem-pci devices
>> results in
>>     "virtio-pmem-pci not supported on this bus"
>>
>> Reasons is, that the bus does not support hotplug and, therefore, does
>> not have a hotplug handler. Let's allow coldplugging virtio-pmem devices
>> on such buses. The hotplug order is only relevant for virtio-pmem-pci
>> when the guest is already alive and the device is visible before
>> memory_device_plug() wired up the memory device bits.
>>
>> Hotplug attempts will still fail with:
>>     "Error: Bus 'pcie.0' does not support hotplugging"
>>
>> Hotunplug attempts will still fail with:
>>     "Error: Bus 'pcie.0' does not support hotplugging"
>>
>> Reported-by: Vivek Goyal <vgoyal@redhat.com>
>> Cc: Pankaj Gupta <pankaj.gupta.linux@gmail.com>
>> Cc: Igor Mammedov <imammedo@redhat.com>
>> Cc: Paolo Bonzini <pbonzini@redhat.com>
>> Cc: Richard Henderson <rth@twiddle.net>
>> Cc: Eduardo Habkost <ehabkost@redhat.com>
>> Cc: "Michael S. Tsirkin" <mst@redhat.com>
>> Cc: Marcel Apfelbaum <marcel.apfelbaum@gmail.com>
>> Signed-off-by: David Hildenbrand <david@redhat.com>
>> ---
>>  hw/i386/pc.c | 18 ++++++++++--------
>>  1 file changed, 10 insertions(+), 8 deletions(-)
> 
> Thanks for the patch David. I still seem to face a different error though.
> 
> 2020-05-26T13:26:05.720617Z qemu-system-x86_64: -device virtio-pmem-pci,memdev=pmem1,id=nv1: memory devices (e.g. for memory hotplug) are not enabled, please specify the maxmem option
> 
> Following is my domain xml file.
> 
> Vivek

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)

@Pankaj, do we have a virtio-pmem doc somewhere describing how to set it up?

-- 
Thanks,

David / dhildenb