linux-kernel - [PATCH v8 07/10] kgdb: Expose default CPUs roundup fallback mechanism

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Message-ID: <20230419155341.v8.7.I21d92f8974c8e4001a5982fea6c98da1bed33ef5@changeid>
Date:   Wed, 19 Apr 2023 15:56:01 -0700
From:   Douglas Anderson <dianders@...omium.org>
To:     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>,
        Mark Rutland <mark.rutland@....com>
Cc:     ito-yuichi@...itsu.com, kgdb-bugreport@...ts.sourceforge.net,
        Chen-Yu Tsai <wens@...e.org>,
        Masayoshi Mizuma <msys.mizuma@...il.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Ard Biesheuvel <ardb@...nel.org>,
        "Rafael J . Wysocki" <rafael.j.wysocki@...el.com>,
        linux-arm-kernel@...ts.infradead.org,
        Stephen Boyd <swboyd@...omium.org>,
        Lecopzer Chen <lecopzer.chen@...iatek.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        linux-perf-users@...r.kernel.org,
        Douglas Anderson <dianders@...omium.org>,
        Jason Wessel <jason.wessel@...driver.com>,
        linux-kernel@...r.kernel.org
Subject: [PATCH v8 07/10] kgdb: Expose default CPUs roundup fallback mechanism

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

Add a new API kgdb_smp_call_nmi_hook() to expose default CPUs roundup
mechanism to a particular archichecture as a runtime fallback if it
detects to not support NMI roundup.

Currently such an architecture example is arm64 supporting pseudo NMIs
feature which is only available on platforms which have support for GICv3
or later version.

Signed-off-by: Sumit Garg <sumit.garg@...aro.org>
Tested-by: Chen-Yu Tsai <wens@...e.org>
Signed-off-by: Douglas Anderson <dianders@...omium.org>
---

(no changes since v1)

 include/linux/kgdb.h      | 12 ++++++++++++
 kernel/debug/debug_core.c |  8 +++++++-
 2 files changed, 19 insertions(+), 1 deletion(-)

diff --git a/include/linux/kgdb.h b/include/linux/kgdb.h
index 258cdde8d356..87713bd390f3 100644
--- a/include/linux/kgdb.h
+++ b/include/linux/kgdb.h
@@ -199,6 +199,18 @@ kgdb_arch_handle_qxfer_pkt(char *remcom_in_buffer,
 
 extern void kgdb_call_nmi_hook(void *ignored);
 
+/**
+ *	kgdb_smp_call_nmi_hook - Provide default fallback mechanism to
+ *				 round-up CPUs
+ *
+ *	If you're using the default implementation of kgdb_roundup_cpus()
+ *	this function will be called.  And if an arch detects at runtime to
+ *	not support NMI based roundup then it can fallback to default
+ *	mechanism using this API.
+ */
+
+extern void kgdb_smp_call_nmi_hook(void);
+
 /**
  *	kgdb_roundup_cpus - Get other CPUs into a holding pattern
  *
diff --git a/kernel/debug/debug_core.c b/kernel/debug/debug_core.c
index d5e9ccde3ab8..14d40a7d6a4b 100644
--- a/kernel/debug/debug_core.c
+++ b/kernel/debug/debug_core.c
@@ -238,7 +238,7 @@ NOKPROBE_SYMBOL(kgdb_call_nmi_hook);
 static DEFINE_PER_CPU(call_single_data_t, kgdb_roundup_csd) =
 	CSD_INIT(kgdb_call_nmi_hook, NULL);
 
-void __weak kgdb_roundup_cpus(void)
+void kgdb_smp_call_nmi_hook(void)
 {
 	call_single_data_t *csd;
 	int this_cpu = raw_smp_processor_id();
@@ -269,6 +269,12 @@ void __weak kgdb_roundup_cpus(void)
 			kgdb_info[cpu].rounding_up = false;
 	}
 }
+NOKPROBE_SYMBOL(kgdb_smp_call_nmi_hook);
+
+void __weak kgdb_roundup_cpus(void)
+{
+	kgdb_smp_call_nmi_hook();
+}
 NOKPROBE_SYMBOL(kgdb_roundup_cpus);
 
 #endif
-- 
2.40.0.634.g4ca3ef3211-goog