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Subject[PATCH RFC 4/5] s390/speculation: Add support for 'cpu_spec_mitigations=' cmdline options
Date
Configure s390 runtime CPU speculation bug mitigations in accordance
with the 'cpu_spec_mitigations=' cmdline options. This affects Spectre
v1 and Spectre v2.

The default behavior is unchanged.

Signed-off-by: Josh Poimboeuf <jpoimboe@redhat.com>
---
Documentation/admin-guide/kernel-parameters.txt | 7 ++++---
arch/s390/kernel/nospec-branch.c | 4 +++-
2 files changed, 7 insertions(+), 4 deletions(-)

diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt
index 0e8eae1e8a25..e838af96daa4 100644
--- a/Documentation/admin-guide/kernel-parameters.txt
+++ b/Documentation/admin-guide/kernel-parameters.txt
@@ -2554,8 +2554,9 @@
Disable all speculative CPU mitigations.
Equivalent to: nopti [x86, powerpc]
nospectre_v1 [powerpc]
- nospectre_v2 [x86]
+ nospectre_v2 [x86, powerpc, s390]
spectre_v2_user=off [x86]
+ nobp=0 [s390]
spec_store_bypass_disable=off [x86, powerpc]
l1tf=off [x86]

@@ -2567,7 +2568,7 @@
upgrades, or who have other ways of avoiding
SMT-based attacks.
Equivalent to: pti=auto [x86]
- spectre_v2=auto [x86]
+ spectre_v2=auto [x86, s390]
spectre_v2_user=auto [x86]
spec_store_bypass_disable=auto [x86, powerpc]
l1tf=flush [x86]
@@ -2578,7 +2579,7 @@
always want to be fully mitigated, even if it
means losing SMT.
Equivalent to: pti=auto [x86]
- spectre_v2=auto [x86]
+ spectre_v2=auto [x86, s390]
spectre_v2_user=auto [x86]
spec_store_bypass_disable=auto [x86, powerpc]
l1tf=flush,nosmt [x86]
diff --git a/arch/s390/kernel/nospec-branch.c b/arch/s390/kernel/nospec-branch.c
index bdddaae96559..c40eb672b43a 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 +59,8 @@ early_param("nospectre_v2", nospectre_v2_setup_early);

void __init nospec_auto_detect(void)
{
- if (test_facility(156)) {
+ if (test_facility(156) ||
+ cpu_spec_mitigations == CPU_SPEC_MITIGATIONS_OFF) {
/*
* The machine supports etokens.
* Disable expolines and disable nobp.
--
2.17.2
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