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Date:   Mon, 17 Oct 2022 11:00:46 -0300
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Subject: Re: [PATCH V3 01/11] ARM: Disable FIQs (but not IRQs) on CPUs
 shutdown paths
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From:   "Guilherme G. Piccoli" <gpiccoli@igalia.com>
To:     Russell King <linux@armlinux.org.uk>,
        Marc Zyngier <maz@kernel.org>,
        linux-arm-kernel@lists.infradead.org, will@kernel.org,
        Mark Rutland <mark.rutland@arm.com>, arnd@arndb.de,
        Catalin Marinas <catalin.marinas@arm.com>
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On 18/09/2022 10:58, Guilherme G. Piccoli wrote:
> On 19/08/2022 19:17, Guilherme G. Piccoli wrote:
>> 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. IRQs are architecturally masked when we
>> take an interrupt, but FIQs are high priority than IRQs, hence they
>> aren't masked. With that said, it makes sense to disable FIQs here,
>> but there's no need for (re-)disabling IRQs.
>>
>> More than that: there is an alternative path for disabling CPUs,
>> in the form of function crash_smp_send_stop(), which is used for
>> kexec/panic path. This function relies on a SMP call that also
>> triggers a busy-wait loop [at machine_crash_nonpanic_core()], but
>> without disabling FIQs. This might lead to odd scenarios, like
>> early interrupts in the boot of kexec'd kernel or even interrupts
>> in secondary "disabled" CPUs while the main one still works in the
>> panic path and assumes all secondary CPUs are (really!) off.
>>
>> So, let's disable FIQs in both paths and *not* disable IRQs a second
>> time, since they are already masked in both paths by the architecture.
>> This way, we keep both CPU quiesce paths consistent and safe.
>>
>> Cc: Marc Zyngier <maz@kernel.org>
>> Cc: Michael Kelley <mikelley@microsoft.com>
>> Cc: Russell King <linux@armlinux.org.uk>
>> Signed-off-by: Guilherme G. Piccoli <gpiccoli@igalia.com>
>>

Monthly ping - let me know if there's something I should improve in
order this fix is considered!
Thanks,


Guilherme