Re: [RFC Design Doc] Add vNVDIMM support for Xen

[Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>]

> Then there is another problem (which also exists in the current
> design): does Xen need to emulate NVDIMM _DSM for dom0? Take the _DSM
> that access label storage area (for namespace) for example:

No. And it really can't as each vendors _DSM is different - and there
is no ACPI AML interpreter inside Xen hypervisor.
> 
> The way Linux reserving space on pmem mode NVDIMM is to leave the
> reserved space at the beginning of pmem mode NVDIMM and create a pmem
> namespace which starts from the end of the reserved space. Because the
> reservation information is written in the namespace in the NVDIMM
> label storage area, every OS that follows the namespace spec would not
> mistakenly write files in the reserved area. I prefer to the same way
> if Xen is going to do the reservation. We definitely don't want dom0
> to break the label storage area, so Xen seemingly needs to emulate the
> corresponding _DSM functions for dom0? If so, which part, the
> hypervisor or the toolstack, should do the emulation?

But we do not want Xen to do the reservation. The control guest (Dom0)
is the one that will mount the NVDIMM, and extract the system ranges
from the files on the NVDIMM - and glue them to a guest. 

It is also the job of Dom0 to do the actually partition the NVDIMM
as fit. Actually let me step back. It is the job of the guest who
has the full NVDIMM in it. At bootup it is Dom0 - but you can very
well 'unplug' the NVDIMM from Dom0 and assign it wholesale to a guest.

Granted at that point the _DSM operations have to go through QEMU
which ends up calling the dom0 ioctls on PMEM to do the operation
(like getting the SMART data).
> 
> Haozhong

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