Re: [Qemu-stable] [Qemu-devel] [PATCH] pc: acpi: revert back to 1 SRAT entry for hotpluggable area

[Igor Mammedov]

On Thu, 23 Aug 2018 14:25:01 -0300
Eduardo Habkost <address@hidden> wrote:

> On Thu, Aug 23, 2018 at 10:14:06AM +0200, Igor Mammedov wrote:
> > On Wed, 22 Aug 2018 15:01:12 -0300
> > Eduardo Habkost <address@hidden> wrote:  
> [...]
> > > However, have you considered keeping adding separate entries for
> > > NVDIMM devices only (so we follow the spec), but add a single
> > > (numa_nodes-1, MEM_AFFINITY_HOTPLUGGABLE|MEM_AFFINITY_ENABLED)
> > > entry to the rest?  
> > Indeed, I did. It doesn't work either.  
> 
> When exactly it didn't work?  Did nvdimm + memory hotplug ever
> worked together on Windows guests?
before 848a1cc1e QEMU CLI with nvdimm + memory hotplug worked
as expected for Windows.
With approach you suggested, it would create several SRAT entries
X for nvdimm and Y for the rest (1 in the best case or many if
nvdimms/pc-dimms are interleaved) and that breaks memory hotplug.
 
> For all the other cases there should be absolutely no difference:
> 
> nvdimm users would still get a spec-compliant SRAT table (like on
> QEMU 3.0).
> 
> Memory hotplug users w/o nvdimm would get the same ACPI table
> that they would get after applying this patch (i.e. the one we
> had before commit 848a1cc1e ("hw/acpi-build: build SRAT memory
> affinity structures for DIMM devices").
I did consider it. It still would be a regression but a minor one
(only Windows nvdimm enabled cases will have regressed memory
hotplug). I even have a patch for it, but it's still a regression,
that's why I've posted full 848a1cc1e revert.

If it were a bug in the newest version of windows (assuming it's
proven Windows bug), I'd be inclined towards being spec compliant
and let MS fix Windows as it was with CPU hotplug (hijacked ACPI0010
container) which they eventually fixed, but in this case it affects
all guests versions and there is no proof that's a Windows bug.

So my hope here is that Intel has resources to figure out what
Windows expectations are wrt SRAT/memory layout and memory hotplug.