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

From: Jan Beulich
Date: Wed Oct 12 2016 - 03:25:48 EST

>>> On 11.10.16 at 17:53, <dan.j.williams@xxxxxxxxx> wrote:
> On Tue, Oct 11, 2016 at 6:08 AM, Jan Beulich <jbeulich@xxxxxxxx> wrote:
>>>>> Andrew Cooper <andrew.cooper3@xxxxxxxxxx> 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.
> The missing piece for me is why this reservation for control data
> needs to be done in the libnvdimm core? I would expect that any dax
> capable file could be mapped and made available to a guest. This
> includes /dev/ramX devices that are dax capable, but are external to
> the libnvdimm sub-system.

Despite me being the only one on the To list, I don't think the question
was really meant to be directed to me.