[PATCH RFC 16/17] arm64: text replication: early kernel option to enable replication

[Russell King (Oracle)]

Provide an early kernel option "ktext=" which allows the kernel text
replication to be enabled. This takes a boolean argument.

The way this has been implemented means that we take all the same paths
through the kernel at runtime whether kernel text replication has been
enabled or not; this allows the performance effects of the code changes
to be evaluated separately from the act of running with replicating the
kernel text.

Signed-off-by: Russell King (Oracle) <rmk+kernel at armlinux.org.uk>
---
 .../admin-guide/kernel-parameters.txt          |  5 +++++
 arch/arm64/mm/ktext.c                          | 18 ++++++++++++++++++
 2 files changed, 23 insertions(+)

diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt
index 9e5bab29685f..684bd004816e 100644
--- a/Documentation/admin-guide/kernel-parameters.txt
+++ b/Documentation/admin-guide/kernel-parameters.txt
@@ -2488,6 +2488,11 @@
 			0: force disabled
 			1: force enabled
 
+	ktext=		[ARM64] Control kernel text replication on NUMA
+			machines. Default: disabled.
+			0: disable kernel text replication
+			1: enable kernel text replication
+
 	kunit.enable=	[KUNIT] Enable executing KUnit tests. Requires
 			CONFIG_KUNIT to be set to be fully enabled. The
 			default value can be overridden via
diff --git a/arch/arm64/mm/ktext.c b/arch/arm64/mm/ktext.c
index f64a649f06a4..ec2d474bbd2c 100644
--- a/arch/arm64/mm/ktext.c
+++ b/arch/arm64/mm/ktext.c
@@ -98,6 +98,21 @@ void ktext_replication_patch_alternative(__le32 *src, int nr_inst)
 	}
 }
 
+static bool ktext_enabled;
+
+static int __init parse_ktext(char *str)
+{
+	bool enabled;
+	int ret = strtobool(str, &enabled);
+
+	if (ret)
+		return ret;
+
+	ktext_enabled = enabled;
+	return 0;
+}
+early_param("ktext", parse_ktext);
+
 /* Allocate page tables and memory for the replicated kernel texts. */
 void __init ktext_replication_init(void)
 {
@@ -119,6 +134,9 @@ void __init ktext_replication_init(void)
 		return;
 	}
 
+	if (!ktext_enabled)
+		return;
+
 	for_each_node(nid) {
 		/* Nothing to do for node 0 */
 		if (!nid)
-- 
2.30.2