RE: [PATCH 02/30] ARM: kexec: Disable IRQs/FIQs also on crash CPUs shutdown path

["Michael Kelley (LINUX)" <mikelley@xxxxxxxxxxxxx>]

From: Guilherme G. Piccoli <gpiccoli@xxxxxxxxxx> Sent: Wednesday, April 27, 
2022 3:49 PM
> 
> Currently the regular CPU shutdown path for ARM disables IRQs/FIQs
> in the secondary CPUs - smp_send_stop() calls ipi_cpu_stop(), which
> is responsible for that. This makes sense, since we're turning off
> such CPUs, putting them in an endless busy-wait loop.
> 
> Problem is that there is an alternative path for disabling CPUs,
> in the form of function crash_smp_send_stop(), used for kexec/panic
> paths. This functions relies in a SMP call that also triggers a

s/functions relies in/function relies on/

> busy-wait loop [at machine_crash_nonpanic_core()], but *without*
> disabling interrupts. This might lead to odd scenarios, like early
> interrupts in the boot of kexec'd kernel or even interrupts in
> other CPUs while the main one still works in the panic path and
> assumes all secondary CPUs are (really!) off.
> 
> This patch mimics the ipi_cpu_stop() interrupt disable mechanism
> in the crash CPU shutdown path, hence disabling IRQs/FIQs in all
> secondary CPUs in the kexec/panic path as well.
> 
> Cc: Marc Zyngier <maz@xxxxxxxxxx>
> Cc: Russell King <linux@xxxxxxxxxxxxxxx>
> Signed-off-by: Guilherme G. Piccoli <gpiccoli@xxxxxxxxxx>
> ---
>  arch/arm/kernel/machine_kexec.c | 3 +++
>  1 file changed, 3 insertions(+)
> 
> diff --git a/arch/arm/kernel/machine_kexec.c b/arch/arm/kernel/machine_kexec.c
> index f567032a09c0..ef788ee00519 100644
> --- a/arch/arm/kernel/machine_kexec.c
> +++ b/arch/arm/kernel/machine_kexec.c
> @@ -86,6 +86,9 @@ void machine_crash_nonpanic_core(void *unused)
>       set_cpu_online(smp_processor_id(), false);
>       atomic_dec(&waiting_for_crash_ipi);
> 
> +     local_fiq_disable();
> +     local_irq_disable();
> +
>       while (1) {
>               cpu_relax();
>               wfe();
> --
> 2.36.0