From: Josh Poimboeuf <jpoimboe@redhat.com>
Date: Tue, 2 Apr 2019 09:59:33 -0500
Subject: x86/speculation/mds: Add mds=full,nosmt cmdline option
Git-repo: tip/tip
Git-commit: d71eb0ce109a124b0fa714832823b9452f2762cf
Patch-mainline: Queued in a subsystem tree
References: bsc#1111331, CVE-2018-12126, CVE-2018-12127, CVE-2018-12130, CVE-2019-11091

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>
Acked-by: Borislav Petkov <bp@suse.de>
---
 Documentation/admin-guide/kernel-parameters.txt |    6 ++++--
 Documentation/x86/mds.rst                       |    4 ++++
 arch/x86/kernel/cpu/bugs.c                      |   10 ++++++++++
 3 files changed, 18 insertions(+), 2 deletions(-)

--- a/arch/x86/kernel/cpu/bugs.c
+++ b/arch/x86/kernel/cpu/bugs.c
@@ -342,6 +342,7 @@ early_param("l1tf", l1tf_cmdline);
 
 /* 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",
@@ -359,8 +360,13 @@ static void __init mds_select_mitigation
 	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]);
 }
 
@@ -376,6 +382,10 @@ 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;
 }
--- a/Documentation/admin-guide/kernel-parameters.txt
+++ b/Documentation/admin-guide/kernel-parameters.txt
@@ -2221,8 +2221,10 @@
 			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.
--- a/Documentation/x86/mds.rst
+++ b/Documentation/x86/mds.rst
@@ -119,6 +119,10 @@ Kernel internal mitigation modes
 	  scenarios where the host has the updated microcode but the
 	  hypervisor does not expose MD_CLEAR in CPUID. It's a best
 	  effort approach without guarantee.
+
+  full,nosmt	The same as mds=full, with SMT disabled on vulnerable
+		CPUs.  This is the complete mitigation.
+
  ======= ============================================================
 
 If the CPU is affected and mds=off is not supplied on the kernel command