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

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

> >>>>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 interface,
> >>_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 about
> >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 dom0

Yes of course it can.
> handle all the things like native. If it can not, dom0 can interpret ACPI and fetch
> 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 PFN.
> 
> 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).

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 for
the NVDIMM. Based on that - you will know what kind of exposure the hypervisor
needs to the _FIT and NFIT tables.

(Adding Feng Wu, the VT-d maintainer).