From d71eb0ce109a124b0fa714832823b9452f2762cf Mon Sep 17 00:00:00 2001
From: Josh Poimboeuf <jpoimboe@redhat.com>
Date: Tue, 2 Apr 2019 09:59:33 -0500
Subject: [PATCH] x86/speculation/mds: Add mds=full,nosmt cmdline option
Add the mds=full,nosmt cmdline option. This is like mds=full, but with
SMT disabled if the CPU is vulnerable.
Signed-off-by: Josh Poimboeuf <jpoimboe@redhat.com>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Reviewed-by: Tyler Hicks <tyhicks@canonical.com>
Acked-by: Jiri Kosina <jkosina@suse.cz>
---
Documentation/admin-guide/hw-vuln/mds.rst | 3 +++
Documentation/admin-guide/kernel-parameters.txt | 6 ++++--
arch/x86/kernel/cpu/bugs.c | 10 ++++++++++
3 files changed, 17 insertions(+), 2 deletions(-)
diff --git a/Documentation/admin-guide/hw-vuln/mds.rst b/Documentation/admin-guide/hw-vuln/mds.rst
index 1de29d28903d0..244ab47d1fb3a 100644
--- a/Documentation/admin-guide/hw-vuln/mds.rst
+++ b/Documentation/admin-guide/hw-vuln/mds.rst
@@ -260,6 +260,9 @@ time with the option "mds=". The valid arguments for this option are:
It does not automatically disable SMT.
+ full,nosmt The same as mds=full, with SMT disabled on vulnerable
+ CPUs. This is the complete mitigation.
+
off Disables MDS mitigations completely.
============ =============================================================
diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt
index 7325319c2c23c..8f04985d3122d 100644
--- a/Documentation/admin-guide/kernel-parameters.txt
+++ b/Documentation/admin-guide/kernel-parameters.txt
@@ -2372,8 +2372,10 @@
This parameter controls the MDS mitigation. The
options are:
- full - Enable MDS mitigation on vulnerable CPUs
- off - Unconditionally disable MDS mitigation
+ full - Enable MDS mitigation on vulnerable CPUs
+ full,nosmt - Enable MDS mitigation and disable
+ SMT on vulnerable CPUs
+ off - Unconditionally disable MDS mitigation
Not specifying this option is equivalent to
mds=full.
diff --git a/arch/x86/kernel/cpu/bugs.c b/arch/x86/kernel/cpu/bugs.c
index 373ae1dcd3016..9f252082a83b6 100644
--- a/arch/x86/kernel/cpu/bugs.c
+++ b/arch/x86/kernel/cpu/bugs.c
@@ -221,6 +221,7 @@ static void x86_amd_ssb_disable(void)
/* Default mitigation for L1TF-affected CPUs */
static enum mds_mitigations mds_mitigation __ro_after_init = MDS_MITIGATION_FULL;
+static bool mds_nosmt __ro_after_init = false;
static const char * const mds_strings[] = {
[MDS_MITIGATION_OFF] = "Vulnerable",
@@ -238,8 +239,13 @@ static void __init mds_select_mitigation(void)
if (mds_mitigation == MDS_MITIGATION_FULL) {
if (!boot_cpu_has(X86_FEATURE_MD_CLEAR))
mds_mitigation = MDS_MITIGATION_VMWERV;
+
static_branch_enable(&mds_user_clear);
+
+ if (mds_nosmt && !boot_cpu_has(X86_BUG_MSBDS_ONLY))
+ cpu_smt_disable(false);
}
+
pr_info("%s\n", mds_strings[mds_mitigation]);
}
@@ -255,6 +261,10 @@ static int __init mds_cmdline(char *str)
mds_mitigation = MDS_MITIGATION_OFF;
else if (!strcmp(str, "full"))
mds_mitigation = MDS_MITIGATION_FULL;
+ else if (!strcmp(str, "full,nosmt")) {
+ mds_mitigation = MDS_MITIGATION_FULL;
+ mds_nosmt = true;
+ }
return 0;
}
--
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