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Re: [Xen-devel] [PATCH 4/4] hvmloader: add support to load extra ACPI tables from qemu


On 01/20/2016 06:15 PM, Haozhong Zhang wrote:

CCing QEMU vNVDIMM maintainer: Xiao Guangrong

Conceptually, an NVDIMM is just like a fast SSD which is linearly mapped
into memory.  I am still on the dom0 side of this fence.

The real question is whether it is possible to take an NVDIMM, split it
in half, give each half to two different guests (with appropriate NFIT
tables) and that be sufficient for the guests to just work.

Yes, one NVDIMM device can be split into multiple parts and assigned
to different guests, and QEMU is responsible to maintain virtual NFIT
tables for each part.

Either way, it needs to be a toolstack policy decision as to how to
split the resource.

Currently, we are using NVDIMM as a block device and a DAX-based filesystem
is created upon it in Linux so that file-related accesses directly reach
the NVDIMM device.

In KVM, If the NVDIMM device need to be shared by different VMs, we can
create multiple files on the DAX-based filesystem and assign the file to
each VMs. In the future, we can enable namespace (partition-like) for PMEM
memory and assign the namespace to each VMs (current Linux driver uses the
whole PMEM as a single namespace).

I think it is not a easy work to let Xen hypervisor recognize NVDIMM device
and manager NVDIMM resource.


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