[SRU][Xenial][PATCH] UBUNTU: SAUCE: x86/speculation: Only report IBPB/IBRS state changes

[Juerg Haefliger]

Only print the IBPB/IBRS state to the log if it actually changes. Otherwise
the log is polluted everytime the procfs file is read from.

Signed-off-by: Juerg Haefliger <juergh at canonical.com>
---
 kernel/sysctl.c | 18 +++++++++++-------
 1 file changed, 11 insertions(+), 7 deletions(-)

diff --git a/kernel/sysctl.c b/kernel/sysctl.c
index 11c626dd1b1c..59fe90f934fb 100644
--- a/kernel/sysctl.c
+++ b/kernel/sysctl.c
@@ -213,15 +213,17 @@ static unsigned int __ibpb_enabled = 0;   /* procfs shadow variable */
 int set_ibpb_enabled(unsigned int val)
 {
 	int error = 0;
+	unsigned int prev = ibpb_enabled;
 
 	mutex_lock(&spec_ctrl_mutex);
 
 	/* Only enable IBPB if the CPU supports it */
 	if (boot_cpu_has(X86_FEATURE_IBPB)) {
 		ibpb_enabled = val;
-		pr_info("Spectre V2 : Spectre v2 mitigation: %s Indirect "
-			"Branch Prediction Barrier\n",
-			ibpb_enabled ? "Enabling" : "Disabling");
+		if (ibpb_enabled != prev)
+			pr_info("Spectre V2 : Spectre v2 mitigation: %s "
+				"Indirect Branch Prediction Barrier\n",
+				ibpb_enabled ? "Enabling" : "Disabling");
 	} else {
 		ibpb_enabled = 0;
 		if (val) {
@@ -260,16 +262,18 @@ int set_ibrs_enabled(unsigned int val)
 {
 	int error = 0;
 	unsigned int cpu;
+	unsigned int prev = ibrs_enabled;
 
 	mutex_lock(&spec_ctrl_mutex);
 
 	/* Only enable/disable IBRS if the CPU supports it */
 	if (boot_cpu_has(X86_FEATURE_IBRS)) {
 		ibrs_enabled = val;
-		pr_info("Spectre V2 : Spectre v2 mitigation: %s Indirect "
-			"Branch Restricted Speculation%s\n",
-			ibrs_enabled ? "Enabling" : "Disabling",
-			ibrs_enabled == 2 ? " (user space)" : "");
+		if (ibrs_enabled != prev)
+			pr_info("Spectre V2 : Spectre v2 mitigation: %s "
+				"Indirect Branch Restricted Speculation%s\n",
+				ibrs_enabled ? "Enabling" : "Disabling",
+				ibrs_enabled == 2 ? " (user space)" : "");
 
 		if (ibrs_enabled == 0) {
 			/* Always disable IBRS */
-- 
2.19.1