Re: [PATCH 2/2] pc-nvdimm acpi: build ACPI tables for pc-nvdimm devices

[Haozhong Zhang <haozhong.zhang@intel.com>]

On 01/05/16 11:00, Stefano Stabellini wrote:
> On Mon, 4 Jan 2016, Konrad Rzeszutek Wilk wrote:
> > On Mon, Jan 04, 2016 at 04:01:08PM +0000, Stefano Stabellini wrote:
> > > CC'ing the Xen tools maintainers and Anthony.
> > > 
> > > On Tue, 29 Dec 2015, Haozhong Zhang wrote:
> > > > Reuse existing NVDIMM ACPI code to build ACPI tables for pc-nvdimm
> > > > devices. The resulting tables are then copied into Xen guest domain so
> > > > tha they can be later loaded by Xen hvmloader.
> > > > 
> > > > Signed-off-by: Haozhong Zhang <haozhong.zhang@intel.com>
> > > 
> > > How much work would it be to generate the nvdimm acpi tables from the
> > > Xen toolstack?
> > 
> > Why duplicate the code? The QEMU generates the NFIT tables and its sub-tables.
> >
> >
> > > Getting the tables from QEMU doesn't seem like a good idea to me, unless
> > > we start getting the whole set of ACPI tables that way.
> > 
> > There is also the ACPI DSDT code - which requires an memory region
> > to be reserved for the AML code to drop the parameters so that QEMU
> > can scan the NVDIMM for failures. The region (and size) should be
> > determined by QEMU since it works on this data.
> 
> QEMU can generate the whole set of ACPI tables. Why should we take only
> the nvdimm tables and not the others?
>
NVDIMM tables are the only tables required to support vNVDIMM in this
patch series, and they are self-contained and not conflict with other
existing tables built by hvmloader. For other tables built by QEMU, I
have no idea whether they could work with Xen, so I only take nvdimm
tables from QEMU.

> I don't think it is wise to have two components which both think are in
> control of generating ACPI tables, hvmloader (soon to be the toolstack
> with Anthony's work) and QEMU. From an architectural perspective, it
> doesn't look robust to me.
>
Do you mean whenever nvdimm code in QEMU is changed, we would have to
make more efforts to ensure it still works with Xen?

> Could we take this opportunity to switch to QEMU generating the whole
> set of ACPI tables?
>
Not quite sure how much effort would be taken on this change. CCed
hvmloader maintainers for their comments.

Thanks,
Haozhong