Re: [PATCH 0/4] add support for vNVDIMM

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

On 01/20/16 14:54, Andrew Cooper wrote:
> On 20/01/16 14:47, Zhang, Haozhong wrote:
> > On 01/20/16 14:35, Stefano Stabellini wrote:
> >> On Wed, 20 Jan 2016, Zhang, Haozhong wrote:
> >>> On 01/20/16 12:43, Stefano Stabellini wrote:
> >>>> On Wed, 20 Jan 2016, Tian, Kevin wrote:
> >>>>>> From: Zhang, Haozhong
> >>>>>> Sent: Tuesday, December 29, 2015 7:32 PM
> >>>>>>
> >>>>>> This patch series is the Xen part patch to provide virtual NVDIMM to
> >>>>>> guest. The corresponding QEMU patch series is sent separately with the
> >>>>>> title "[PATCH 0/2] add vNVDIMM support for Xen".
> >>>>>>
> >>>>>> * Background
> >>>>>>
> >>>>>>  NVDIMM (Non-Volatile Dual In-line Memory Module) is going to be
> >>>>>>  supported on Intel's platform. NVDIMM devices are discovered via ACPI
> >>>>>>  and configured by _DSM method of NVDIMM device in ACPI. Some
> >>>>>>  documents can be found at
> >>>>>>  [1] ACPI 6: http://www.uefi.org/sites/default/files/resources/ACPI_6.0.pdf
> >>>>>>  [2] NVDIMM Namespace: http://pmem.io/documents/NVDIMM_Namespace_Spec.pdf
> >>>>>>  [3] DSM Interface Example:
> >>>>>> http://pmem.io/documents/NVDIMM_DSM_Interface_Example.pdf
> >>>>>>  [4] Driver Writer's Guide:
> >>>>>> http://pmem.io/documents/NVDIMM_Driver_Writers_Guide.pdf
> >>>>>>
> >>>>>>  The upstream QEMU (commits 5c42eef ~ 70d1fb9) has added support to
> >>>>>>  provide virtual NVDIMM in PMEM mode, in which NVDIMM devices are
> >>>>>>  mapped into CPU's address space and are accessed via normal memory
> >>>>>>  read/write and three special instructions (clflushopt/clwb/pcommit).
> >>>>>>
> >>>>>>  This patch series and the corresponding QEMU patch series enable Xen
> >>>>>>  to provide vNVDIMM devices to HVM domains.
> >>>>>>
> >>>>>> * Design
> >>>>>>
> >>>>>>  Supporting vNVDIMM in PMEM mode has three requirements.
> >>>>>>
> >>>>> Although this design is about vNVDIMM, some background of how pNVDIMM
> >>>>> is managed in Xen would be helpful to understand the whole design since
> >>>>> in PMEM mode you need map pNVDIMM into GFN addr space so there's
> >>>>> a matter of how pNVDIMM is allocated.
> >>>> Yes, some background would be very helpful. Given that there are so many
> >>>> moving parts on this (Xen, the Dom0 kernel, QEMU, hvmloader, libxl)
> >>>> I suggest that we start with a design document for this feature.
> >>> Let me prepare a design document. Basically, it would include
> >>> following contents. Please let me know if you want anything additional
> >>> to be included.
> >> Thank you!
> >>
> >>
> >>> * What NVDIMM is and how it is used
> >>> * Software interface of NVDIMM
> >>>   - ACPI NFIT: what parameters are recorded and their usage
> >>>   - ACPI SSDT: what _DSM methods are provided and their functionality
> >>>   - New instructions: clflushopt/clwb/pcommit
> >>> * How the linux kernel drives NVDIMM
> >>>   - ACPI parsing
> >>>   - Block device interface
> >>>   - Partition NVDIMM devices
> >>> * How KVM/QEMU implements vNVDIMM
> >> This is a very good start.
> >>
> >>
> >>> * What I propose to implement vNVDIMM in Xen
> >>>   - Xen hypervisor/toolstack: new instruction enabling and address mapping
> >>>   - Dom0 Linux kernel: host NVDIMM driver
> >>>   - QEMU: virtual NFIT/SSDT, _DSM handling, and role in address mapping
> >> This is OK. It might be also good to list other options that were
> >> discussed, but it is certainly not necessary in first instance.
> > I'll include them.
> >
> > And one thing missed above:
> > * What I propose to implement vNVDIMM in Xen
> >   - Building vNFIT and vSSDT: copy them from QEMU to Xen toolstack
> >
> > I know it is controversial and will record other options and my reason
> > for this choice.
> 
> Please would you split the subjects of "how to architect guest NVDIMM
> support in Xen" from "how to get suitable ACPI tables into a guest". 
> The former depends on the latter, but they are two different problems to
> solve and shouldn't be conflated in one issue.
> 
> ~Andrew
>

Sure.

Haozhong