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

[Stefano Stabellini <stefano.stabellini@xxxxxxxxxxxxx>]

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.

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