linux-kernel - [tip:core/speculation] s390/speculation: Support 'mitigations=' cmdline option

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Date:   Wed, 17 Apr 2019 13:03:30 -0700
From:   tip-bot for Josh Poimboeuf <tipbot@...or.com>
To:     linux-tip-commits@...r.kernel.org
Cc:     hpa@...or.com, luto@...nel.org, bp@...en8.de, jpoimboe@...hat.com,
        tyhicks@...onical.com, tglx@...utronix.de, aarcange@...hat.com,
        longman@...hat.com, catalin.marinas@....com, peterz@...radead.org,
        gregkh@...uxfoundation.org, benh@...nel.crashing.org,
        jcm@...hat.com, paulus@...ba.org, pauld@...hat.com,
        mingo@...nel.org, jkosina@...e.cz, will.deacon@....com,
        heiko.carstens@...ibm.com, mpe@...erman.id.au,
        schwidefsky@...ibm.com, linux-kernel@...r.kernel.org,
        torvalds@...ux-foundation.org, jikos@...nel.org,
        rdunlap@...radead.org, steven.price@....com
Subject: [tip:core/speculation] s390/speculation: Support 'mitigations='
 cmdline option

Commit-ID:  0336e04a6520bdaefdb0769d2a70084fa52e81ed
Gitweb:     https://git.kernel.org/tip/0336e04a6520bdaefdb0769d2a70084fa52e81ed
Author:     Josh Poimboeuf <jpoimboe@...hat.com>
AuthorDate: Fri, 12 Apr 2019 15:39:31 -0500
Committer:  Thomas Gleixner <tglx@...utronix.de>
CommitDate: Wed, 17 Apr 2019 21:37:29 +0200

s390/speculation: Support 'mitigations=' cmdline option

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@...hat.com>
Signed-off-by: Thomas Gleixner <tglx@...utronix.de>
Tested-by: Jiri Kosina <jkosina@...e.cz> (on x86)
Reviewed-by: Jiri Kosina <jkosina@...e.cz>
Cc: Borislav Petkov <bp@...en8.de>
Cc: "H . Peter Anvin" <hpa@...or.com>
Cc: Andy Lutomirski <luto@...nel.org>
Cc: Peter Zijlstra <peterz@...radead.org>
Cc: Jiri Kosina <jikos@...nel.org>
Cc: Waiman Long <longman@...hat.com>
Cc: Andrea Arcangeli <aarcange@...hat.com>
Cc: Jon Masters <jcm@...hat.com>
Cc: Benjamin Herrenschmidt <benh@...nel.crashing.org>
Cc: Paul Mackerras <paulus@...ba.org>
Cc: Michael Ellerman <mpe@...erman.id.au>
Cc: linuxppc-dev@...ts.ozlabs.org
Cc: Martin Schwidefsky <schwidefsky@...ibm.com>
Cc: Heiko Carstens <heiko.carstens@...ibm.com>
Cc: linux-s390@...r.kernel.org
Cc: Catalin Marinas <catalin.marinas@....com>
Cc: Will Deacon <will.deacon@....com>
Cc: linux-arm-kernel@...ts.infradead.org
Cc: linux-arch@...r.kernel.org
Cc: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Cc: Tyler Hicks <tyhicks@...onical.com>
Cc: Linus Torvalds <torvalds@...ux-foundation.org>
Cc: Randy Dunlap <rdunlap@...radead.org>
Cc: Steven Price <steven.price@....com>
Cc: Phil Auld <pauld@...hat.com>
Link: https://lkml.kernel.org/r/e4a161805458a5ec88812aac0307ae3908a030fc.1555085500.git.jpoimboe@redhat.com

---
 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 ac7150a25a7a..1ae93872b79f 100644
--- a/Documentation/admin-guide/kernel-parameters.txt
+++ b/Documentation/admin-guide/kernel-parameters.txt
@@ -2514,7 +2514,7 @@
 			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.
@@ -2525,7 +2525,8 @@
 				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.