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

On 01/21/2016 01:18 AM, Konrad Rzeszutek Wilk wrote:
c) hotplug support

How does that work? Ah the _DSM will point to the new ACPI NFIT for the OS
to scan. That would require the hypervisor also reading this for it to
update it's data-structures.

Similar as you said. The NVDIMM root device in SSDT/DSDT dedicates a new 
_FIT, which return the new NFIT once new device hotplugged. And yes, domain 0 is
the better place handing this case too.

That one is a bit difficult. Both the OS and the hypervisor would need to know 
this (I think?). dom0 since it gets the ACPI event and needs to process it. Then
the hypervisor needs to be told so it can slurp it up.

Can dom0 receive the interrupt triggered by device hotplug? If yes, we can let 

Yes of course it can.
handle all the things like native. If it can not, dom0 can interpret ACPI and 
the irq info out and tell hypervior to pass the irq to dom0, it is doable?

However I don't know if the hypervisor needs to know all the details of an
NVDIMM - or just the starting and ending ranges so that when an guest is created
and the VT-d is constructed - it can be assured that the ranges are valid.

I am not an expert on the P2M code - but I think that would need to be looked
at to make sure it is OK with stitching an E820_NVDIMM type "MFN" into an guest 

We do better do not use "E820" as it lacks some advantages of ACPI, such as, 
NUMA, hotplug,
lable support (namespace)...

<hand-waves> I don't know what QEMU does for guests? I naively assumed it would
create an E820_NVDIMM along with the ACPI MADT NFIT tables (and the SSDT to have
the _DSM).

Ah, ACPI eliminates this E820 entry.

Either way what I think you need to investigate is what is neccessary for the
Xen hypervisor VT-d code (IOMMU) to have an entry which is the system address 
the NVDIMM. Based on that - you will know what kind of exposure the hypervisor
needs to the _FIT and NFIT tables.

Interesting. I did not consider using NVDIMM as DMA. Do you have usecase for 
kind of NVDIMM usage?

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