Re: [PATCH V3 01/11] ARM: Disable FIQs (but not IRQs) on CPUs shutdown paths

From: "Russell King (Oracle)" <linux@armlinux.org.uk>
To: "Guilherme G. Piccoli" <gpiccoli@igalia.com>
Cc: 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>,
	kexec@lists.infradead.org, pmladek@suse.com, bhe@redhat.com,
	akpm@linux-foundation.org, linux-kernel@vger.kernel.org,
	linux-hyperv@vger.kernel.org, netdev@vger.kernel.org,
	x86@kernel.org, kernel-dev@igalia.com, kernel@gpiccoli.net,
	halves@canonical.com, fabiomirmar@gmail.com,
	alejandro.j.jimenez@oracle.com,
	andriy.shevchenko@linux.intel.com, bp@alien8.de, corbet@lwn.net,
	d.hatayama@jp.fujitsu.com, dave.hansen@linux.intel.com,
	dyoung@redhat.com, feng.tang@intel.com,
	gregkh@linuxfoundation.org, mikelley@microsoft.com,
	hidehiro.kawai.ez@hitachi.com, jgross@suse.com,
	john.ogness@linutronix.de, keescook@chromium.org,
	luto@kernel.org, mhiramat@kernel.org, mingo@redhat.com,
	paulmck@kernel.org, peterz@infradead.org, rostedt@goodmis.org,
	senozhatsky@chromium.org, stern@rowland.harvard.edu,
	tglx@linutronix.de, vgoyal@redhat.com, vkuznets@redhat.com,
	xuqiang36@huawei.com
Subject: Re: [PATCH V3 01/11] ARM: Disable FIQs (but not IRQs) on CPUs shutdown paths
Date: Mon, 17 Oct 2022 15:17:35 +0100	[thread overview]
Message-ID: <Y01j/3qKUvj346AH@shell.armlinux.org.uk> (raw)
In-Reply-To: <8e30b99e-70ed-7d5a-ea1f-3b0fadb644bc@igalia.com>

On Mon, Oct 17, 2022 at 11:00:46AM -0300, Guilherme G. Piccoli wrote:
> 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!

Patches don't get applied unless they end up in the patch system.
Thanks.

-- 
RMK's Patch system: https://www.armlinux.org.uk/developer/patches/
FTTP is here! 40Mbps down 10Mbps up. Decent connectivity at last!

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