Re: [Qemu-devel] Questions about vNVDIMM on qemu/KVM

[Stefan Hajnoczi <stefanha@gmail.com>]

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On Wed, May 23, 2018 at 02:08:12PM +0900, Yasunori Goto wrote:
> Hello,

CCing Pankaj, who is developing virtio-pmem and may have comments beyond
what has already been discussed.

> I'm investigating status of vNVDIMM on qemu/KVM,
> and I have some questions about it. I'm glad if anyone answer them.
> 
> In my understanding, qemu/KVM has a feature to show NFIT for guest,
> and it will be still updated about platform capability with this patch set.
> https://lists.gnu.org/archive/html/qemu-devel/2018-05/msg04756.html
> 
> And libvirt also supports this feature with <memory model='nvdimm'>
> https://libvirt.org/formatdomain.html#elementsMemory
> 
> 
> However, virtio-pmem is developing now, and it is better
> for archtectures to detect regions of NVDIMM without ACPI (like s390x)
> In addition, It is also necessary to flush guest contents on vNVDIMM
> who has a backend-file. 
> 
> 
> Q1) Does ACPI.NFIT bus of qemu/kvm remain with virtio-pmem? 
>     How do each roles become it if both NFIT and virtio-pmem will be available?
>     If my understanding is correct, both NFIT and virtio-pmem is used to
>     detect vNVDIMM regions, but only one seems to be necessary....
> 
>     Otherwize, is the NFIT bus just for keeping compatibility, 
>     and virtio-pmem is promising way?
> 
>     
> Q2) What bus is(will be?) created for virtio-pmem?
>     I could confirm the bus of NFIT is created with <memory model='nvdimm'>,
>     and I heard other bus will be created for virtio-pmem, but I could not
>     find what bus is created concretely.
>     ---
>       # ndctl list -B
>       {
>          "provider":"ACPI.NFIT",
>          "dev":"ndbus0"
>       }
>     ---
>    
>     I think it affects what operations user will be able to, and what 
>     notification is necessary for vNVDIMM. 
>     ACPI defines some operations like namespace controll, and notification
>     for NVDIMM health status or others.
>     (I suppose that other status notification might be necessary for vNVDIMM,
>      but I'm not sure yet...)
> 
> If my understanding is wrong, please correct me.
> 
> Thanks,
> ---
> Yasunori Goto
> 
> 
> 

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