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

[Haozhong Zhang <haozhong.zhang@intel.com>]

On 10/09/16 20:45, Dan Williams wrote:
> On Sun, Oct 9, 2016 at 5:35 PM, Haozhong Zhang <haozhong.zhang@intel.com> 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
> >   https://lists.xenproject.org/archives/html/xen-devel/2016-07/msg01921.html.
> 
> 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.

> The usage of fiemap and the sysfs resource for the pmem device, as
> mentioned in the design document, does not seem to comprehend that
> file block allocations may be discontiguous and may change over time
> depending on the file.

True. I may need to find a way to notify Xen of the underlying
changes, so that Xen can then adjust the address mapping.

Thanks,
Haozhong