Re: [PATCH v4 2/7] hw/s390x/virtio-ccw: Always inject NMI to first CPU

[Cornelia Huck <cohuck@redhat.com>]

On Tue, Aug 11 2026, Philippe Mathieu-Daudé <philmd@oss.qualcomm.com> wrote:

> From: Philippe Mathieu-Daudé <philmd@linaro.org>
>
> We can trigger NMI from HMP or QMP.
>
> QEMU maps the NMI to the s390x per-CPU 'RESTART' interrupt.
> Linux guests usually setup this interrupt to trigger kdump
> or crash. Such crashdump can be triggered in QEMU by HMP
> "nmi" or QMP "inject-nmi" commands.
>
> Using QMP, since we can not select a particular CPU, the first
> CPU is used (CPU#0). See the documentation from commit 795dc6e4
> ("watchdog: Add new Virtual Watchdog action INJECT-NMI"):
>
>   @inject-nmi: a non-maskable interrupt is injected into the
>                first VCPU (all VCPUS on x86) (since 2.4)
>
> While we can select a particular CPU on HMP, the guest behavior
> is expected to be the same if using CPU #N or CPU #0. Since
> always using CPU#0 simplifies API maintainance, update s390_nmi()
> to inject NMI to the first CPU.

In theory, we could have different actions setup for different cpus. In
practice, Linux does not do that, and I'm not sure if anything else we
might run does -- especially as we always end up with CPU 0 for QMP
anyway.

So I'm fine with getting rid of the different behaviour between HMP and
QMP, especially as it allows simplifying the code.

>
> Signed-off-by: Philippe Mathieu-Daudé <philmd@linaro.org>
> Reviewed-by: Peter Maydell <peter.maydell@linaro.org>
> Reviewed-by: David Hildenbrand <david@redhat.com>
> Signed-off-by: Philippe Mathieu-Daudé <philmd@oss.qualcomm.com>
> ---
>  qapi/machine.json          | 7 ++++---
>  qapi/run-state.json        | 6 ++++--
>  hw/s390x/s390-virtio-ccw.c | 4 +---
>  hmp-commands.hx            | 5 +++--
>  4 files changed, 12 insertions(+), 10 deletions(-)

Acked-by: Cornelia Huck <cohuck@redhat.com>