Re: [Xen-devel] [RFC Design Doc] Add vNVDIMM support for Xen

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> On 17.03.16 at 14:29, <haozhong.zhang@xxxxxxxxx> wrote:
> On 03/17/16 06:59, Jan Beulich wrote:
>> >>> On 17.03.16 at 13:44, <haozhong.zhang@xxxxxxxxx> wrote:
>> > Hmm, making Xen has full control could at least make reserving space
>> > on NVDIMM easier. I guess full control does not include manipulating
>> > file systems on NVDIMM which can be still left to dom0?
>> > 
>> > Then there is another problem (which also exists in the current
>> > design): does Xen need to emulate NVDIMM _DSM for dom0? Take the _DSM
>> > that access label storage area (for namespace) for example:
>> > 
>> > The way Linux reserving space on pmem mode NVDIMM is to leave the
>> > reserved space at the beginning of pmem mode NVDIMM and create a pmem
>> > namespace which starts from the end of the reserved space. Because the
>> > reservation information is written in the namespace in the NVDIMM
>> > label storage area, every OS that follows the namespace spec would not
>> > mistakenly write files in the reserved area. I prefer to the same way
>> > if Xen is going to do the reservation. We definitely don't want dom0
>> > to break the label storage area, so Xen seemingly needs to emulate the
>> > corresponding _DSM functions for dom0? If so, which part, the
>> > hypervisor or the toolstack, should do the emulation?
>> 
>> I don't think I can answer all but the very last point: Of course this
>> can't be done in the tool stack, since afaict the Dom0 kernel will
>> want to evaluate _DSM before the tool stack even runs.
> 
> Or, we could modify dom0 kernel to just use the label storage area as is
> and does not modify it. Can xen hypervisor trust dom0 kernel in this aspect?

I think so, yes.

Jan


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