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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>,
        "coresight@...ts.linaro.org" <coresight@...ts.linaro.org>,
        "linuxppc-dev@...ts.ozlabs.org" <linuxppc-dev@...ts.ozlabs.org>,
        "linux-alpha@...r.kernel.org" <linux-alpha@...r.kernel.org>,
        "linux-arm-kernel@...ts.infradead.org" 
        <linux-arm-kernel@...ts.infradead.org>,
        "linux-edac@...r.kernel.org" <linux-edac@...r.kernel.org>,
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        "fabiomirmar@...il.com" <fabiomirmar@...il.com>,
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        "andriy.shevchenko@...ux.intel.com" 
        <andriy.shevchenko@...ux.intel.com>,
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        "john.ogness@...utronix.de" <john.ogness@...utronix.de>,
        "keescook@...omium.org" <keescook@...omium.org>,
        "luto@...nel.org" <luto@...nel.org>,
        "mhiramat@...nel.org" <mhiramat@...nel.org>,
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        "tglx@...utronix.de" <tglx@...utronix.de>,
        "vgoyal@...hat.com" <vgoyal@...hat.com>,
        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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