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

[Eduardo Habkost]

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.

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).

-- 
Eduardo