[PATCH v5] powerpc/64s: support nospectre_v2 cmdline option

[Christopher M. Riedl]

Add support for disabling the kernel implemented spectre v2 mitigation
(count cache flush on context switch) via the nospectre_v2 and
mitigations=off cmdline options.

Suggested-by: Michael Ellerman <m...@ellerman.id.au>
Signed-off-by: Christopher M. Riedl <c...@informatik.wtf>
Reviewed-by: Andrew Donnellan <a...@linux.ibm.com>
---
v4->v5:
        Fix checkpatch complaint
 arch/powerpc/kernel/security.c | 19 ++++++++++++++++---
 1 file changed, 16 insertions(+), 3 deletions(-)

diff --git a/arch/powerpc/kernel/security.c b/arch/powerpc/kernel/security.c
index e1c9cf079503..7cfcb294b11c 100644
--- a/arch/powerpc/kernel/security.c
+++ b/arch/powerpc/kernel/security.c
@@ -28,7 +28,7 @@ static enum count_cache_flush_type count_cache_flush_type = 
COUNT_CACHE_FLUSH_NO
 bool barrier_nospec_enabled;
 static bool no_nospec;
 static bool btb_flush_enabled;
-#ifdef CONFIG_PPC_FSL_BOOK3E
+#if defined(CONFIG_PPC_FSL_BOOK3E) || defined(CONFIG_PPC_BOOK3S_64)
 static bool no_spectrev2;
 #endif
 
@@ -114,7 +114,7 @@ static __init int security_feature_debugfs_init(void)
 device_initcall(security_feature_debugfs_init);
 #endif /* CONFIG_DEBUG_FS */
 
-#ifdef CONFIG_PPC_FSL_BOOK3E
+#if defined(CONFIG_PPC_FSL_BOOK3E) || defined(CONFIG_PPC_BOOK3S_64)
 static int __init handle_nospectre_v2(char *p)
 {
        no_spectrev2 = true;
@@ -122,6 +122,9 @@ static int __init handle_nospectre_v2(char *p)
        return 0;
 }
 early_param("nospectre_v2", handle_nospectre_v2);
+#endif /* CONFIG_PPC_FSL_BOOK3E || CONFIG_PPC_BOOK3S_64 */
+
+#ifdef CONFIG_PPC_FSL_BOOK3E
 void setup_spectre_v2(void)
 {
        if (no_spectrev2 || cpu_mitigations_off())
@@ -399,7 +402,17 @@ static void toggle_count_cache_flush(bool enable)
 
 void setup_count_cache_flush(void)
 {
-       toggle_count_cache_flush(true);
+       bool enable = true;
+
+       if (no_spectrev2 || cpu_mitigations_off()) {
+               if (security_ftr_enabled(SEC_FTR_BCCTRL_SERIALISED) ||
+                   security_ftr_enabled(SEC_FTR_COUNT_CACHE_DISABLED))
+                       pr_warn("Spectre v2 mitigations not under software 
control, can't disable\n");
+
+               enable = false;
+       }
+
+       toggle_count_cache_flush(enable);
 }
 
 #ifdef CONFIG_DEBUG_FS
-- 
2.21.0