[PATCH v4 1/5] arm64: Add framework to turn IPI as NMI

[Sumit Garg]

Hi Masa,

On Sat, 10 Oct 2020 at 20:43, Masayoshi Mizuma <msys.mizuma at gmail.com> wrote:
>
> On Sat, Oct 10, 2020 at 10:34:04AM +0100, Marc Zyngier wrote:
> > On Sat, 10 Oct 2020 02:58:55 +0100,
> > Masayoshi Mizuma <msys.mizuma at gmail.com> wrote:
> >
> > [...]
> >
> > > > +void ipi_nmi_setup(int cpu)
> > > > +{
> > > > + if (!ipi_desc)
> > > > +         return;
> > >
> > > ipi_nmi_setup() may be called twice for CPU0:
> > >
> > >   set_smp_ipi_range => set_smp_ipi_nmi => ipi_nmi_setup
> > >                     => ipi_setup => ipi_nmi_setup
> > >
> > > Actually, I got the following error message via the second ipi_nmi_setup():
> > >
> > >   GICv3: Pseudo-NMIs enabled using relaxed ICC_PMR_EL1 synchronisation
> > >   GICv3: Cannot set NMI property of enabled IRQ 8
> > >   genirq: Failed to setup NMI delivery: irq 8
> > >

Ah, thanks for catching this which I missed during my testing.

> > > Why don't we have a check to prevent that? Like as:
> > >
> > >        if (cpumask_test_cpu(cpu, ipi_desc->percpu_enabled))
> > >                return;
> >
> > That's definitely the wrong thing to do. prepare_nmi_setup() shouldn't
> > be called twice, and papering over it isn't acceptable.
>
> Got it. How about moving ipi_nmi_setup() from ipi_setup() to
> secondary_start_kernel() ? so that CPU0 can call ipi_nmi_setup() only
> from set_smp_ipi_nmi().
>
> --- a/arch/arm64/kernel/smp.c
> +++ b/arch/arm64/kernel/smp.c
> @@ -245,6 +245,7 @@ asmlinkage notrace void secondary_start_kernel(void)
>         notify_cpu_starting(cpu);
>
>         ipi_setup(cpu);
> +       ipi_nmi_setup(cpu);
>
>         store_cpu_topology(cpu);
>         numa_add_cpu(cpu);
> @@ -966,8 +967,6 @@ static void ipi_setup(int cpu)
>
>         for (i = 0; i < nr_ipi; i++)
>                 enable_percpu_irq(ipi_irq_base + i, 0);
> -
> -       ipi_nmi_setup(cpu);
>  }
>
>  #ifdef CONFIG_HOTPLUG_CPU
>

IMO, it would be more consistent to keep invocation of ipi_nmi_setup()
from ipi_setup(). So let me remove other invocation from
set_smp_ipi_nmi():

diff --git a/arch/arm64/kernel/ipi_nmi.c b/arch/arm64/kernel/ipi_nmi.c
index d3aa430..000e457 100644
--- a/arch/arm64/kernel/ipi_nmi.c
+++ b/arch/arm64/kernel/ipi_nmi.c
@@ -87,7 +87,4 @@ void __init set_smp_ipi_nmi(int ipi)
        ipi_desc = irq_to_desc(ipi);
        irq_set_status_flags(ipi, IRQ_HIDDEN);
        ipi_id = ipi;
-
-       /* Setup the boot CPU immediately */
-       ipi_nmi_setup(smp_processor_id());
 }

Do let me know if this works for you?

-Sumit

> Thanks,
> Masa