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Date: Mon, 10 Oct 2016 17:43:10 +0100
From: Andrew Cooper <andrew.cooper3@...rix.com>
To: Haozhong Zhang <haozhong.zhang@...el.com>,
<linux-nvdimm@...ts.01.org>, <xen-devel@...ts.xenproject.org>
CC: Juergen Gross <jgross@...e.com>,
Xiao Guangrong <guangrong.xiao@...ux.intel.com>,
Andrew Morton <akpm@...ux-foundation.org>,
Arnd Bergmann <arnd@...db.de>,
Johannes Thumshirn <jthumshirn@...e.de>,
<linux-kernel@...r.kernel.org>,
Stefano Stabellini <stefano@...reto.com>,
David Vrabel <david.vrabel@...rix.com>,
Ross Zwisler <ross.zwisler@...ux.intel.com>,
Boris Ostrovsky <boris.ostrovsky@...cle.com>,
Dan Williams <dan.j.williams@...el.com>
Subject: Re: [Xen-devel] [RFC KERNEL PATCH 0/2] Add Dom0 NVDIMM support for
Xen
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
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