Re: [Qemu-devel] Default CPU for NMI injection (QMP and IPMI)

[Corey Minyard]

On 09/22/2016 01:42 PM, Eduardo Habkost wrote:
> On Wed, Sep 21, 2016 at 03:38:25PM -0500, Corey Minyard wrote:
> > On 09/21/2016 03:20 PM, Eduardo Habkost wrote:
> > > Hi,
> > >
> > > I was looking at the monitor code handling the "current CPU", and
> > > noticed that qmp_inject_nmi() looks suspicious: it is a QMP
> > > command, but uses monitor_get_cpu_index().
> > >
> > > In addition to the "inject-nmi" QMP command, qmp_inject_nmi() is
> > > used at:
> > > * hmp_inject_nmi()
> > > * ipmi_do_hw_op() (IPMI_SEND_NMI operation)
> > >
> > > This confused me, so I would like to know:
> > >
> > > 1) What exactly "default CPU" is supposed to mean in the
> > >      "inject-nmi" QMP command documentation?
> > > 2) To which CPU(s) are NMIs supposed to be sent when triggered by
> > >      IPMI messages? I don't know how to test the IPMI code, but it
> > >      looks like it will crash if QEMU runs without any monitor.
> > It doesn't matter which CPU it goes to.
> OK, so in the case of IPMI we can make it send the NMI to the
> first CPU.
>
> > I haven't tested without a monitor, so I'm not sure.  Does
> > another interface into the NMI code need to be added?
> There's another interface, already: nmi_monitor_handle() already
> gets a cpu_index argument and doesn't depend on the monitor code.
> We could change the IPMI code to call
> nmi_monitor_handle(first_cpu->cpu_index) directly.

Ok, I'll make a change for this, unless we decide to fix it
another way.

> In the case of the inject-nmi QMP command, I need to understand
> what "default CPU" is supposed to mean in the inject-nmi
> documentation. Maybe it can be changed to use the first CPU, too
> (that's probably the existing behavior because there's no way to
> change cur_mon->mon_cpu in a QMP monitor).
I looked through is a bit, and the only place I found it was used was
the x390 code.

If we remove the CPU index from this, then the IPMI device can
keep the same interface.

Thanks,

-corey