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Date: Fri, 29 Apr 2022 16:26:02 +0000
From: "Michael Kelley (LINUX)" <mikelley@...rosoft.com>
To: "Guilherme G. Piccoli" <gpiccoli@...lia.com>,
"akpm@...ux-foundation.org" <akpm@...ux-foundation.org>,
"bhe@...hat.com" <bhe@...hat.com>,
"pmladek@...e.com" <pmladek@...e.com>,
"kexec@...ts.infradead.org" <kexec@...ts.infradead.org>
CC: "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
"bcm-kernel-feedback-list@...adcom.com"
<bcm-kernel-feedback-list@...adcom.com>,
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vkuznets <vkuznets@...hat.com>,
"will@...nel.org" <will@...nel.org>, Marc Zyngier <maz@...nel.org>,
Russell King <linux@...linux.org.uk>
Subject: RE: [PATCH 02/30] ARM: kexec: Disable IRQs/FIQs also on crash CPUs
shutdown path
From: Guilherme G. Piccoli <gpiccoli@...lia.com> 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@...nel.org>
> Cc: Russell King <linux@...linux.org.uk>
> Signed-off-by: Guilherme G. Piccoli <gpiccoli@...lia.com>
> ---
> 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
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