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

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Message-Id: <57FCF26A02000078000F15E0@prv-mh.provo.novell.com>
Date:   Tue, 11 Oct 2016 07:08:42 -0600
From:   "Jan Beulich" <jbeulich@...e.com>
To:     <andrew.cooper3@...rix.com>
Cc:     <stefano@...reto.com>, <arnd@...db.de>, <david.vrabel@...rix.com>,
        <dan.j.williams@...el.com>, <haozhong.zhang@...el.com>,
        <akpm@...ux-foundation.org>, <guangrong.xiao@...ux.intel.com>,
        <ross.zwisler@...ux.intel.com>, <linux-nvdimm@...ts.01.org>,
        <xen-devel@...ts.xenproject.org>, <boris.ostrovsky@...cle.com>,
        "Juergen Gross" <JGross@...e.com>, <jthumshirn@...e.de>,
        <linux-kernel@...r.kernel.org>
Subject: Re: [Xen-devel] [RFC KERNEL PATCH 0/2] Add Dom0 NVDIMM support
 for Xen

>>> Andrew Cooper <andrew.cooper3@...rix.com> 10/10/16 6:44 PM >>>
>On 10/10/16 01:35, Haozhong Zhang wrote:
>> 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.
>
>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.

That precludes the use as RAM extension, and I thought earlier rounds of
discussion had got everyone in agreement that at least for the pmem case
we will need some control data in Xen.

Jan