linux-kernel - [PATCH v7 6/7] kgdb: Expose default CPUs roundup fallback mechanism

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Date:   Mon,  2 Nov 2020 17:14:46 +0530
From:   Sumit Garg <sumit.garg@...aro.org>
To:     maz@...nel.org, catalin.marinas@....com, will@...nel.org,
        daniel.thompson@...aro.org
Cc:     linux-arm-kernel@...ts.infradead.org, tglx@...utronix.de,
        jason@...edaemon.net, linux@...linux.org.uk,
        tsbogend@...ha.franken.de, mpe@...erman.id.au, davem@...emloft.net,
        mingo@...hat.com, bp@...en8.de, x86@...nel.org,
        mark.rutland@....com, julien.thierry.kdev@...il.com,
        dianders@...omium.org, jason.wessel@...driver.com,
        msys.mizuma@...il.com, ito-yuichi@...itsu.com,
        kgdb-bugreport@...ts.sourceforge.net, linux-kernel@...r.kernel.org,
        Sumit Garg <sumit.garg@...aro.org>
Subject: [PATCH v7 6/7] kgdb: Expose default CPUs roundup fallback mechanism

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>
---
 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 0d6cf64..4190f13 100644
--- a/include/linux/kgdb.h
+++ b/include/linux/kgdb.h
@@ -200,6 +200,18 @@ 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
  *
  *	On SMP systems, we need to get the attention of the other CPUs
diff --git a/kernel/debug/debug_core.c b/kernel/debug/debug_core.c
index 1e75a89..ae785d8 100644
--- a/kernel/debug/debug_core.c
+++ b/kernel/debug/debug_core.c
@@ -241,7 +241,7 @@ void __weak kgdb_call_nmi_hook(void *ignored)
 }
 NOKPROBE_SYMBOL(kgdb_call_nmi_hook);
 
-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();
@@ -273,6 +273,12 @@ 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
-- 
2.7.4