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

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

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.

* 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
* 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

Haozhong