linux-kernel - [PATCH v9 4/7] arm64: smp: Assign and setup the debug IPI

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Date:   Thu,  1 Jun 2023 14:31:48 -0700
From:   Douglas Anderson <dianders@...omium.org>
To:     Mark Rutland <mark.rutland@....com>,
        Catalin Marinas <catalin.marinas@....com>,
        Will Deacon <will@...nel.org>,
        Sumit Garg <sumit.garg@...aro.org>,
        Daniel Thompson <daniel.thompson@...aro.org>,
        Marc Zyngier <maz@...nel.org>
Cc:     linux-perf-users@...r.kernel.org, ito-yuichi@...itsu.com,
        Chen-Yu Tsai <wens@...e.org>, Ard Biesheuvel <ardb@...nel.org>,
        Stephen Boyd <swboyd@...omium.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        linux-arm-kernel@...ts.infradead.org,
        kgdb-bugreport@...ts.sourceforge.net,
        Masayoshi Mizuma <msys.mizuma@...il.com>,
        "Rafael J . Wysocki" <rafael.j.wysocki@...el.com>,
        Lecopzer Chen <lecopzer.chen@...iatek.com>,
        Douglas Anderson <dianders@...omium.org>,
        Ben Dooks <ben-linux@...ff.org>,
        Ingo Molnar <mingo@...nel.org>,
        Josh Poimboeuf <jpoimboe@...nel.org>,
        Valentin Schneider <vschneid@...hat.com>,
        linux-kernel@...r.kernel.org
Subject: [PATCH v9 4/7] arm64: smp: Assign and setup the debug IPI

From: Sumit Garg <sumit.garg@...aro.org>

All current arm64 interrupt controllers have at least 8
IPIs. Currently we are only using 7 of them on arm64. Let's use the
8th one as a debug IPI. This uses the new "debug IPI" infrastructure
which will try to allocate this IPI as an NMI/pseudo NMI if possible.

Signed-off-by: Sumit Garg <sumit.garg@...aro.org>
Signed-off-by: Douglas Anderson <dianders@...omium.org>
---
I could imagine that people object to using up the last free IPI on
interrupt controllers with only 8 IPIs. However, it shouldn't be a big
deal. If we later need an extra IPI, it shouldn't be too hard to
combine some of the existing ones. Presumably we could just get rid of
the "crash stop" IPI and have the normal "stop" IPI do the crash if
"waiting_for_crash_ipi" is non-zero

Changes in v9:
- Add a warning if we don't have enough IPIs for the NMI IPI
- Renamed "NMI IPI" to "debug IPI" since it might not be backed by NMI.
- Update commit description

Changes in v8:
- debug_ipi_setup() and debug_ipi_teardown() no longer take cpu param

 arch/arm64/kernel/smp.c | 11 +++++++++++
 1 file changed, 11 insertions(+)

diff --git a/arch/arm64/kernel/smp.c b/arch/arm64/kernel/smp.c
index edd63894d61e..db019b49d3bd 100644
--- a/arch/arm64/kernel/smp.c
+++ b/arch/arm64/kernel/smp.c
@@ -53,6 +53,8 @@
 
 #include <trace/events/ipi.h>
 
+#include "ipi_debug.h"
+
 DEFINE_PER_CPU_READ_MOSTLY(int, cpu_number);
 EXPORT_PER_CPU_SYMBOL(cpu_number);
 
@@ -935,6 +937,8 @@ static void ipi_setup(int cpu)
 
 	for (i = 0; i < nr_ipi; i++)
 		enable_percpu_irq(ipi_irq_base + i, 0);
+
+	debug_ipi_setup();
 }
 
 #ifdef CONFIG_HOTPLUG_CPU
@@ -947,6 +951,8 @@ static void ipi_teardown(int cpu)
 
 	for (i = 0; i < nr_ipi; i++)
 		disable_percpu_irq(ipi_irq_base + i);
+
+	debug_ipi_teardown();
 }
 #endif
 
@@ -968,6 +974,11 @@ void __init set_smp_ipi_range(int ipi_base, int n)
 		irq_set_status_flags(ipi_base + i, IRQ_HIDDEN);
 	}
 
+	if (n > nr_ipi)
+		set_smp_debug_ipi(ipi_base + nr_ipi);
+	else
+		WARN(1, "Not enough IPIs for NMI IPI\n");
+
 	ipi_irq_base = ipi_base;
 
 	/* Setup the boot CPU immediately */
-- 
2.41.0.rc2.161.g9c6817b8e7-goog