From 54f58c169ed6ae9ef1e533ef8aa4687173b8600c Mon Sep 17 00:00:00 2001
From: Michael Ellerman <mpe@ellerman.id.au>
Date: Wed, 10 Jan 2018 03:07:15 +1100
Subject: [PATCH 08/10] powerpc/64s: Support disabling RFI flush with
 no_rfi_flush and nopti

References: bsc#1068032
Patch-mainline: v4.15-rc8
Git-commit: bc9c9304a45480797e13a8e1df96ffcf44fb62fe

Because there may be some performance overhead of the RFI flush, add
kernel command line options to disable it.

We add a sensibly named 'no_rfi_flush' option, but we also hijack the
x86 option 'nopti'. The RFI flush is not the same as KPTI, but if we
see 'nopti' we can guess that the user is trying to avoid any overhead
of Meltdown mitigations, and it means we don't have to educate every
one about a different command line option.

Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Acked-by: Michal Suchanek <msuchanek@suse.de>
---
 arch/powerpc/kernel/setup_64.c | 24 +++++++++++++++++++++++-
 1 file changed, 23 insertions(+), 1 deletion(-)

diff --git a/arch/powerpc/kernel/setup_64.c b/arch/powerpc/kernel/setup_64.c
index 402cc5337c8d..7e34cbdd5080 100644
--- a/arch/powerpc/kernel/setup_64.c
+++ b/arch/powerpc/kernel/setup_64.c
@@ -774,8 +774,29 @@ early_initcall(disable_hardlockup_detector);
 #ifdef CONFIG_PPC_BOOK3S_64
 static enum l1d_flush_type enabled_flush_types;
 static void *l1d_flush_fallback_area;
+static bool no_rfi_flush;
 bool rfi_flush;
 
+static int __init handle_no_rfi_flush(char *p)
+{
+	pr_info("rfi-flush: disabled on command line.");
+	no_rfi_flush = true;
+	return 0;
+}
+early_param("no_rfi_flush", handle_no_rfi_flush);
+
+/*
+ * The RFI flush is not KPTI, but because users will see doco that says to use
+ * nopti we hijack that option here to also disable the RFI flush.
+ */
+static int __init handle_no_pti(char *p)
+{
+	pr_info("rfi-flush: disabling due to 'nopti' on command line.\n");
+	handle_no_rfi_flush(NULL);
+	return 0;
+}
+early_param("nopti", handle_no_pti);
+
 static void do_nothing(void *unused)
 {
 	/*
@@ -846,6 +867,7 @@ void __init setup_rfi_flush(enum l1d_flush_type types, bool enable)
 
 	enabled_flush_types = types;
 
-	rfi_flush_enable(enable);
+	if (!no_rfi_flush)
+		rfi_flush_enable(enable);
 }
 #endif /* CONFIG_PPC_BOOK3S_64 */
-- 
2.13.6