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

From: Dan Williams
Date: Mon Oct 10 2016 - 12:24:32 EST

On Sun, Oct 9, 2016 at 11:32 PM, Haozhong Zhang
<haozhong.zhang@xxxxxxxxx> wrote:
> On 10/09/16 20:45, Dan Williams wrote:
>> On Sun, Oct 9, 2016 at 5:35 PM, Haozhong Zhang <haozhong.zhang@xxxxxxxxx> 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
>> >
>> The KVM enabling for persistent memory does not need this support from
>> the kernel, and as far as I can see neither does Xen. If the
>> hypervisor needs to reserve some space it can simply trim the amount
>> that it hands to the guest.
> Xen does not have the NVDIMM driver, so it cannot operate on NVDIMM
> devices by itself. Instead it relies on the driver in Dom0 Linux to
> probe NVDIMM and make the reservation.

I'm missing something because the design document talks about mmap'ing
files on a DAX filesystem. So, I'm assuming it is similar to the KVM
NVDIMM virtualization case where an mmap range in dom0 is translated
into a guest physical range. The suggestion is to reserve some memory
out of that mapping rather than introduce a new info block /
reservation type to the sub-system.