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

[Christian Borntraeger]

On 09/27/2016 10:51 PM, Eduardo Habkost wrote:
> On Thu, Sep 22, 2016 at 02:49:35PM -0500, Corey Minyard wrote:
>> On 09/22/2016 01:42 PM, Eduardo Habkost wrote:
> [...]
>>> 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.
> 
> s390 maintainers: is the ability to send a NMI to a specific CPU
> really used in s390? The only way to use it today is to use HMP,
> so I guess no management interface really supports it.
> 
> s390-ccw is the only machine that uses the cpu_index parameter.
> If we remove it, it will allow us to simplify the code.
> Otherwise, we will need to extend the inject-nmi command to
> accept a "cpu" parameter.
> 

Doing it always on the first CPU should be ok for Linux guests.
This is wired up to a PSW restart interrupt, which has the same
handler on all CPUs. Originally it was wired up on the real 
old irons as a button, so I assume from a historical perspective
it is ok to not be able to specify the cpu number. Under z/VM it is 
possible to specify the CPU though. I will try to find out
if there is a real use case for specifying the CPU.

Christian