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

[Ross Philipson <ross.philipson@gmail.com>]

On 02/05/2016 08:43 PM, Haozhong Zhang wrote:
> On 02/05/16 09:40, Ross Philipson wrote:
>> On 02/03/2016 09:09 AM, Andrew Cooper wrote:
> [...]
>>> I agree.
>>>
>>> There has to be a single entity responsible for collating the eventual
>>> ACPI handed to the guest, and this is definitely HVMLoader.
>>>
>>> However, it is correct that Qemu create the ACPI tables for the devices
>>> it emulates for the guest.
>>>
>>> We need to agree on a mechanism whereby each entity can provide their
>>> own subset of the ACPI tables to HVMLoader, and have HVMLoader present
>>> the final set properly to the VM.
>>>
>>> There is an existing usecase of passing the Host SLIC table to a VM, for
>>> OEM Versions of Windows.  I believe this is achieved with
>>> HVM_XS_ACPI_PT_{ADDRESS,LENGTH}, but that mechanism is a little
>>> inflexible and could probably do with being made a little more generic.
>>
>> A while back I added a generic mechanism to load extra ACPI tables into a
>> guest, configurable at runtime. It looks like the functionality is still
>> present. That might be an option.
>>
>> Also, following the thread, it wasn't clear if some of the tables like the
>> SSDT for the NVDIMM device and it's _FIT/_DSM methods were something that
>> could be statically created at build time. If it is something that needs to
>> be generated at runtime (e.g. platform specific), I have a library that can
>> generate any AML on the fly and create SSDTs.
>>
>> Anyway just FYI in case this is helpful.
>>
> 
> Hi Ross,
> 
> Thanks for the information!
> 
> SSDT for NVDIMM devices can not be created statically, because the
> number of some items in it can not be determined at build time. For
> example, the number of NVDIMM ACPI namespace devices (_DSM is under it)
> defined in SSDT is determined by the number of vNVDIMM devices in domain
> configuration. FYI, a sample SSDT for NVDIMM looks like
> 
>   Scope (\_SB){
>       Device (NVDR) // NVDIMM Root device
>       {
>           Name (_HID, “ACPI0012”)
>           Method (_STA) {...}
>           Method (_FIT) {...}
>           Method (_DSM, ...) {
>               ...
>           }
>       }
> 
>       Device (NVD0) // 1st NVDIMM Device
>       {
>           Name(_ADR, h0)
>           Method (_DSM, ...) {
>               ...
>           }
>       }
> 
>       Device (NVD1) // 2nd NVDIMM Device
>       {
>           Name(_ADR, h1)
>           Method (_DSM, ...) {
>               ...
>           }
>       }
> 
>       ...
>   }

Makes sense.

> 
> I had ported QEMU's AML builder code as well as NVDIMM ACPI building
> code to hvmloader and it did work, but then there was too much
> duplicated code for vNVDIMM between QEMU and hvmloader for vNVDIMM.
> Therefore, I prefer to let QEMU that emulates vNVDIMM devices
> to build those tables, as in Andrew and Jan's replies.

Yea it looks like QEUM's AML generating code is quite complete nowadays.
Back when I wrote my library there wasn't really much out there. Anyway
this is where it is if there is something that I might generate that is
missing:

https://github.com/OpenXT/xctools/tree/master/libxenacpi


> 
> Thanks,
> Haozhong
> 


-- 
Ross Philipson