Re: [Xen-devel] [RFC KERNEL PATCH 0/2] Add Dom0 NVDIMM support for Xen

[Andrew Cooper]

On 10/10/16 01:35, Haozhong Zhang wrote:
> Overview
> ========
> This RFC kernel patch series along with corresponding patch series of
> Xen, QEMU and ndctl implements Xen vNVDIMM, which can map the host
> NVDIMM devices to Xen HVM domU as vNVDIMM devices.
>
> Xen hypervisor does not include an NVDIMM driver, so it needs the
> assistance from the driver in Dom0 Linux kernel to manage NVDIMM
> devices. We currently only supports NVDIMM devices in pmem mode.
>
> Design and Implementation
> =========================
> The complete design can be found at
>   https://lists.xenproject.org/archives/html/xen-devel/2016-07/msg01921.html.
>
> All patch series can be found at
>   Xen:          https://github.com/hzzhan9/xen.git nvdimm-rfc-v1
>   QEMU:         https://github.com/hzzhan9/qemu.git xen-nvdimm-rfc-v1
>   Linux kernel: https://github.com/hzzhan9/nvdimm.git xen-nvdimm-rfc-v1
>   ndctl:        https://github.com/hzzhan9/ndctl.git pfn-xen-rfc-v1
>
> Xen hypervisor needs assistance from Dom0 Linux kernel for following tasks:
> 1) Reserve an area on NVDIMM devices for Xen hypervisor to place
>    memory management data structures, i.e. frame table and M2P table.
> 2) Report SPA ranges of NVDIMM devices and the reserved area to Xen
>    hypervisor.

Please can we take a step back here before diving down a rabbit hole.


How do pblk/pmem regions appear in the E820 map at boot?  At the very
least, I would expect at least a large reserved region.

Is the MFN information (SPA in your terminology, so far as I can tell)
available in any static APCI tables, or are they only available as a
result of executing AML methods?


If the MFN information is only available via AML, then point 2) is
needed, although the reporting back to Xen should be restricted to a xen
component, rather than polluting the main device driver.

However, I can't see any justification for 1).  Dom0 should not be
involved in Xen's management of its own frame table and m2p.  The mfns
making up the pmem/pblk regions should be treated just like any other
MMIO regions, and be handed wholesale to dom0 by default.

~Andrew