Re: [Qemu-devel] [PATCH] hw/i386: check if nvdimm is enabled before plugging

[Haozhong Zhang]

On 01/13/17 13:17 +0000, Stefan Hajnoczi wrote:
> On Fri, Jan 13, 2017 at 07:56:51PM +0800, Haozhong Zhang wrote:
> > The missing of 'nvdimm' in the machine type option '-M' means NVDIMM
> > is disabled. QEMU should refuse to plug any NVDIMM device in this case
> > and report the misconfiguration.
> >
> > Reported-by: Stefan Hajnoczi <address@hidden>
> > Signed-off-by: Haozhong Zhang <address@hidden>
> > Message-Id: address@hidden
> > Message-Id: address@hidden
> > ---
> >  hw/i386/pc.c | 5 +++++
> >  1 file changed, 5 insertions(+)
> >
> > diff --git a/hw/i386/pc.c b/hw/i386/pc.c
> > index 25e8586..3907609 100644
> > --- a/hw/i386/pc.c
> > +++ b/hw/i386/pc.c
> > @@ -1715,6 +1715,11 @@ static void pc_dimm_plug(HotplugHandler *hotplug_dev,
> >      }
> >
> >      if (object_dynamic_cast(OBJECT(dev), TYPE_NVDIMM)) {
> > +        if (!pcms->acpi_nvdimm_state.is_enabled) {
> > +            error_setg(&local_err,
> > +                       "nvdimm is not enabled: missing 'nvdimm' in '-M'");
> > +            goto out;
> > +        }
>
> A warning is definitely useful to notify users of a possible
> configuration error.

If NVDIMM is plugged at boot time, QEMU with this patch will stop and report a
message like
   qemu-system-x86_64: -device nvdimm,...: nvdimm is not enabled: missing 
'nvdimm' in '-M'

If NVDIMM is plugged via 'device_add' command, QEMU with this patch will report 
a warning message
   nvdimm is not enabled: missing 'nvdimm' in '-M'
and continue to run w/o plugging this device.

> I wonder what happens when you plug an NVDIMM into a motherboard where
> the firmware lacks support.  Does it:
> * Refuse to boot?
> * Treat the DIMM as regular RAM?
> * Boot but the DIMM will not be used by firmware and kernel?

Good question. Guangrong, any idea?

Thanks,
Haozhong

> QEMU should act the same way as real hardware.
>
> Stefan