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

[Stefan Hajnoczi <stefanha@redhat.com>]

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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 <stefanha@redhat.com>
> Signed-off-by: Haozhong Zhang <haozhong.zhang@intel.com>
> Message-Id: 20170112110928.GF4621@stefanha-x1.localdomain
> Message-Id: 20170111093630.2088-1-stefanha@redhat.com
> ---
>  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.

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?

QEMU should act the same way as real hardware.

Stefan

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