From 91788fcb21d008b1b7ac6beae20522725fa78239 Mon Sep 17 00:00:00 2001
From: Josh Poimboeuf <jpoimboe@redhat.com>
Date: Fri, 12 Apr 2019 15:39:31 -0500
Subject: s390/speculation: Support 'mitigations=' cmdline option

commit 0336e04a6520bdaefdb0769d2a70084fa52e81ed upstream

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@redhat.com>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Tested-by: Jiri Kosina <jkosina@suse.cz> (on x86)
Reviewed-by: Jiri Kosina <jkosina@suse.cz>
Cc: Borislav Petkov <bp@alien8.de>
Cc: "H . Peter Anvin" <hpa@zytor.com>
Cc: Andy Lutomirski <luto@kernel.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Jiri Kosina <jikos@kernel.org>
Cc: Waiman Long <longman@redhat.com>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc: Jon Masters <jcm@redhat.com>
Cc: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Cc: Paul Mackerras <paulus@samba.org>
Cc: Michael Ellerman <mpe@ellerman.id.au>
Cc: linuxppc-dev@lists.ozlabs.org
Cc: Martin Schwidefsky <schwidefsky@de.ibm.com>
Cc: Heiko Carstens <heiko.carstens@de.ibm.com>
Cc: linux-s390@vger.kernel.org
Cc: Catalin Marinas <catalin.marinas@arm.com>
Cc: Will Deacon <will.deacon@arm.com>
Cc: linux-arm-kernel@lists.infradead.org
Cc: linux-arch@vger.kernel.org
Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Cc: Tyler Hicks <tyhicks@canonical.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Randy Dunlap <rdunlap@infradead.org>
Cc: Steven Price <steven.price@arm.com>
Cc: Phil Auld <pauld@redhat.com>
Link: https://lkml.kernel.org/r/e4a161805458a5ec88812aac0307ae3908a030fc.1555085500.git.jpoimboe@redhat.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
 arch/s390/kernel/nospec-branch.c | 9 +++++++++
 1 file changed, 9 insertions(+)

(limited to 'arch')

diff --git a/arch/s390/kernel/nospec-branch.c b/arch/s390/kernel/nospec-branch.c
index d5eed651b5ab..83e597688562 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/facility.h>
 #include <asm/nospec-branch.h>
 
@@ -55,8 +56,16 @@ static int __init nospectre_v2_setup_early(char *str)
 }
 early_param("nospectre_v2", nospectre_v2_setup_early);
 
+
 void __init nospec_auto_detect(void)
 {
+	if (cpu_mitigations_off()) {
+		/*
+		 * Disable expolines and disable nobp.
+		 */
+		if (IS_ENABLED(CC_USING_EXPOLINE))
+			nospec_disable = 1;
+		__clear_facility(82, S390_lowcore.alt_stfle_fac_list);
 	if (IS_ENABLED(CC_USING_EXPOLINE)) {
 		/*
 		 * The kernel has been compiled with expolines.
-- 
cgit v1.2.3