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>

diff --git a/Documentation/admin-guide/hw-vuln/mds.rst b/Documentation/admin-guide/hw-vuln/mds.rst
index 1de29d28903d069b4612bc954d1c4d82c71c6438..244ab47d1fb3a367336f659b25a8c33716df64c0 100644 (file)
--- 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 7325319c2c23cf63f6b12c19ae57736ec4dd265c..8f04985d3122d86fea1e6a3bbb158ef1af26049d 100644 (file)
--- 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 373ae1dcd30165cca8549ebb71e29dc03d6a83e1..9f252082a83b6fd97b6e3e89c26ce1829d996170 100644 (file)
--- 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;
 }