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

From: Andrew Cooper
Date: Mon Oct 10 2016 - 12:47:31 EST

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
> All patch series can be found at
> Xen: nvdimm-rfc-v1
> QEMU: xen-nvdimm-rfc-v1
> Linux kernel: xen-nvdimm-rfc-v1
> ndctl: 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.