x86/speculation/mds: Add mds=full,nosmt cmdline option

commit d71eb0ce109a124b0fa714832823b9452f2762cf upstream

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>
(cherry picked from commit 623b724d5e50c15d160799446956ba0d23d4f978)

Orabug: 29526900
CVE: CVE-2018-12126
CVE: CVE-2018-12130
CVE: CVE-2018-12127

Signed-off-by: Mihai Carabas <mihai.carabas@oracle.com>
Reviewed-by: Boris Ostrovsky <boris.ostrovsky@oracle.com>
Conflicts:
	Documentation/admin-guide/kernel-parameters.txt
	arch/x86/kernel/cpu/bugs.c
bugs.64 vs bugs_64.c: different boot command line parsing code
Documentation/admin-guide/kernel-parameters.txt vs Documentation/kernel-parameters.txt

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/kernel-parameters.txt b/Documentation/kernel-parameters.txt
index 91c5d98efdcb713c6e18db6cad3dadf295748a8f..55d180c14e0d645aa173849c41bd2504ef33e099 100644 (file)
--- a/Documentation/kernel-parameters.txt
+++ b/Documentation/kernel-parameters.txt
@@ -2065,8 +2065,10 @@ bytes respectively. Such letter suffixes can also be entirely omitted.
                        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_64.c b/arch/x86/kernel/cpu/bugs_64.c
index 3237a76441a78184b425ee0320b08226fd845794..41b485b160b2d70f3da80fd987dc968926d73b31 100644 (file)
--- a/arch/x86/kernel/cpu/bugs_64.c
+++ b/arch/x86/kernel/cpu/bugs_64.c
@@ -1319,6 +1319,7 @@ void mds_idle_clear_disable(void)
 
 /* Default mitigation for L1TF-affected CPUs */
 static enum mds_mitigations mds_mitigation __read_mostly = MDS_MITIGATION_FULL;
+static bool mds_nosmt = false;
 
 static const char * const mds_strings[] = {
        [MDS_MITIGATION_OFF]    = "Vulnerable",
@@ -1358,6 +1359,8 @@ static void mds_select_mitigation(void)
         if (ret > 0) {
                if (match_option(arg, ret, "off"))
                        mds_mitigation = MDS_MITIGATION_OFF;
+               else if (match_option(arg, ret, "full,nosmt"))
+                       mds_nosmt = true;
                else if (!match_option(arg, ret, "full"))
                        pr_warn("mds: unknown option %s\n", arg);
        }
@@ -1365,7 +1368,12 @@ static void 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);
+
                update_mds_branch_idle();
        }
        pr_info("%s\n", mds_strings[mds_mitigation]);