Re: [Qemu-devel] [Xen-devel] [RFC QEMU PATCH v4 00/10] Implement vNVDIMM for Xen HVM guest

[Anthony PERARD <anthony.perard@citrix.com>]

On Tue, Mar 06, 2018 at 12:16:08PM +0800, Haozhong Zhang wrote:
> On 03/02/18 12:03 +0000, Anthony PERARD wrote:
> > On Wed, Feb 28, 2018 at 05:36:59PM +0800, Haozhong Zhang wrote:
> > > On 02/27/18 17:22 +0000, Anthony PERARD wrote:
> > > > On Thu, Dec 07, 2017 at 06:18:02PM +0800, Haozhong Zhang wrote:
> > > > > This is the QEMU part patches that works with the associated Xen
> > > > > patches to enable vNVDIMM support for Xen HVM domains. Xen relies on
> > > > > QEMU to build guest NFIT and NVDIMM namespace devices, and allocate
> > > > > guest address space for vNVDIMM devices.
> > > > 
> > > > I've got other question, and maybe possible improvements.
> > > > 
> > > > When QEMU build the ACPI tables, it also initialize some MemoryRegion,
> > > > which use more guest memory. Do you know if those regions are used with
> > > > your patch series on Xen?
> > > 
> > > Yes, that's why dm_acpi_size is introduced.
> > > 
> > > > Otherwise, we could try to avoid their
> > > > creation with this:
> > > > In xenfv_machine_options()
> > > > m->rom_file_has_mr = false;
> > > > (setting this in xen_hvm_init() would probably be better, but I havn't
> > > > try)
> > > 
> > > If my memory is correct, simply setting rom_file_has_mr to false does
> > > not work (though I cannot remind the exact reason). I'll have a look
> > > as the code to refresh my memory.
> > 
> > I've played a bit with this idea, but without a proper NVDIMM available
> > for the guest, so I don't know if it's going to work properly without
> > the mr.
> > 
> > To make it work, I had to disable some code in acpi_build_update() that
> > make use of the MemoryRegions, as well as an assert in acpi_setup().
> > After those small hacks, I could boot the guest, and I've check that the
> > expected ACPI tables where there, and they looked correct to my eyes.
> > And least `ndctl list` works and showed the nvdimm (that I have
> > configured on QEMU's cmdline).
> > 
> > But I may not have been far enough with my tests, and maybe something
> > later relies on the MRs, especially the _DSM method that I don't know if
> > it was working properly.
> > 
> > Anyway, that why I proposed the idea, and if we can avoid more
> > uncertainty about how much guest memory QEMU is going to use, that would
> > be good.
> > 
> 
> Yes, I also tested some non-trivial _DSM methods and it looks rom
> files without memory regions can work with Xen after some
> modifications. I'll apply this idea in the next version if no other
> issues are found.

Awesome, thanks.

-- 
Anthony PERARD