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

[Jan Beulich]

>>> On 12.10.16 at 16:58, <haozhong.zhang@xxxxxxxxx> wrote:
> On 10/12/16 05:32 -0600, Jan Beulich wrote:
>>>>> On 12.10.16 at 12:33, <haozhong.zhang@xxxxxxxxx> wrote:
>>> The layout is shown as the following diagram.
>>>
>>> +---------------+-----------+-------+----------+--------------+
>>> | whatever used | Partition | Super | Reserved | /dev/pmem0p1 |
>>> |  by kernel    |   Table   | Block | for Xen  |              |
>>> +---------------+-----------+-------+----------+--------------+
>>>                 \_____________________ _______________________/
>>> 		                      V
>>> 				 /dev/pmem0
>>
>>I have to admit that I dislike this, for not being OS-agnostic.
>>Neither should there be any Xen-specific region, nor should the
>>"whatever used by kernel" one be restricted to just Linux. What
>>I could see is an OS-reserved area ahead of the partition table,
>>the exact usage of which depends on which OS is currently
>>running (and in the Xen case this might be both Xen _and_ the
>>Dom0 kernel, arbitrated by a tbd protocol). After all, when
>>running under Xen, the Dom0 may not have a need for as much
>>control data as it has when running on bare hardware, for it
>>controlling less (if any) of the actual memory ranges when Xen
>>is present.
>>
> 
> Isn't this OS-reserved area still not OS-agnostic, as it requires OS
> to know where the reserved area is?  Or do you mean it's not if it's
> defined by a protocol that is accepted by all OSes?

The latter - we clearly won't get away without some agreement on
where to retrieve position and size of this area. I was simply
assuming that such a protocol already exists.

Jan