[PATCH v2 4/5] s390/speculation: Support 'mitigations=' cmdline option

[Josh Poimboeuf]

Configure s390 runtime CPU speculation bug mitigations in accordance
with the 'mitigations=' cmdline option.  This affects Spectre v1 and
Spectre v2.

The default behavior is unchanged.

Signed-off-by: Josh Poimboeuf <jpoimboe@xxxxxxxxxx>
---
 Documentation/admin-guide/kernel-parameters.txt | 5 +++--
 arch/s390/kernel/nospec-branch.c                | 3 ++-
 2 files changed, 5 insertions(+), 3 deletions(-)

diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt
index a03ab62b69af..e84a01d90e92 100644
--- a/Documentation/admin-guide/kernel-parameters.txt
+++ b/Documentation/admin-guide/kernel-parameters.txt
@@ -2545,7 +2545,7 @@
 			http://repo.or.cz/w/linux-2.6/mini2440.git
 
 	mitigations=
-			[X86,PPC] Control optional mitigations for CPU
+			[X86,PPC,S390] Control optional mitigations for CPU
 			vulnerabilities.  This is a set of curated,
 			arch-independent options, each of which is an
 			aggregation of existing arch-specific options.
@@ -2556,7 +2556,8 @@
 				expose users to several CPU vulnerabilities.
 				Equivalent to: nopti [X86,PPC]
 					       nospectre_v1 [PPC]
-					       nospectre_v2 [X86,PPC]
+					       nobp=0 [S390]
+					       nospectre_v2 [X86,PPC,S390]
 					       spectre_v2_user=off [X86]
 					       spec_store_bypass_disable=off [X86,PPC]
 					       l1tf=off [X86]
diff --git a/arch/s390/kernel/nospec-branch.c b/arch/s390/kernel/nospec-branch.c
index bdddaae96559..649135cbedd5 100644
--- a/arch/s390/kernel/nospec-branch.c
+++ b/arch/s390/kernel/nospec-branch.c
@@ -1,6 +1,7 @@
 // SPDX-License-Identifier: GPL-2.0
 #include <linux/module.h>
 #include <linux/device.h>
+#include <linux/cpu.h>
 #include <asm/nospec-branch.h>
 
 static int __init nobp_setup_early(char *str)
@@ -58,7 +59,7 @@ early_param("nospectre_v2", nospectre_v2_setup_early);
 
 void __init nospec_auto_detect(void)
 {
-	if (test_facility(156)) {
+	if (test_facility(156) || cpu_mitigations_off()) {
 		/*
 		 * The machine supports etokens.
 		 * Disable expolines and disable nobp.
-- 
2.17.2