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

[Xiao Guangrong <guangrong.xiao@xxxxxxxxxxxxxxx>]

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 
> > > > 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).
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 
> for
> 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 
this
kind of NVDIMM usage?

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