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Re: [Qemu-ppc] [Qemu-devel] [PATCH v3 0/3] pc-dimm: factor out MemoryDev

From: David Hildenbrand
Subject: Re: [Qemu-ppc] [Qemu-devel] [PATCH v3 0/3] pc-dimm: factor out MemoryDevice
Date: Mon, 23 Apr 2018 14:50:43 +0200
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:52.0) Gecko/20100101 Thunderbird/52.7.0

On 23.04.2018 14:31, Igor Mammedov wrote:
> On Fri, 20 Apr 2018 14:34:53 +0200
> David Hildenbrand <address@hidden> wrote:
>> Right now we can only map PCDIMM/NVDIMM into guest address space. In the
>> future, we might want to do the same for virtio devices - e.g.
>> virtio-pmem or virtio-mem. Especially, they should be able to live side
>> by side to each other.
>> E.g. the virto based memory devices regions will not be exposed via ACPI
>> and friends. They will be detected just like other virtio devices and
>> indicate the applicable memory region. This makes it possible to also use
>> them on architectures without memory device detection support (e.g. s390x).
>> Let's factor out the memory device code into a MemoryDevice interface.
> A couple of high level questions as relevant code is not here:

Important remark first: We also have s390x with virtio-ccw.

This essentially will also allow s390x guests to have
- memory hotplug via virtio-mem
- fake dax devices via virtio-pmem

>   1. what would hotplug/unplug call chain look like in case of virtio-pmem 
> device
>      (reason I'm asking is that pmem being PCI device would trigger
>       PCI bus hotplug controller and then it somehow should piggyback
>       to Machine provided hotplug handlers, so I wonder what kind of
>       havoc it would cause on hotplug infrastructure)
>   2. why not use PCI bar mapping mechanism to do mapping since pmem is PCI 
> device?  

pmem might be a PCI device, but virtio-pmem is a virtio device (however
it will be exposed via a proxy)


I think both questions are best answered by Pankaj (already on CC).



David / dhildenb

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