x86/speculation/mds: Add 'mitigations=' support for MDS

commit 5c14068f87d04adc73ba3f41c2a303d3c3d1fa12 upstream. Add MDS to the new 'mitigations=' cmdline option. Signed-off-by: Josh Poimboeuf <[email protected]> Signed-off-by: Thomas Gleixner <[email protected]> Signed-off-by: Ben Hutchings <[email protected]> Signed-off-by: Greg Kroah-Hartman <[email protected]>
klaby · May 14, 2019 · 025b9cf · 025b9cf
1 parent 1709284
commit 025b9cf
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diff --git a/Documentation/kernel-parameters.txt b/Documentation/kernel-parameters.txt
@@ -2488,6 +2488,7 @@ bytes respectively. Such letter suffixes can also be entirely omitted.
 					       spectre_v2_user=off [X86]
 					       spec_store_bypass_disable=off [X86]
 					       l1tf=off [X86]
+					       mds=off [X86]
 
 			auto (default)
 				Mitigate all CPU vulnerabilities, but leave SMT
@@ -2502,6 +2503,7 @@ bytes respectively. Such letter suffixes can also be entirely omitted.
 				if needed.  This is for users who always want to
 				be fully mitigated, even if it means losing SMT.
 				Equivalent to: l1tf=flush,nosmt [X86]
+					       mds=full,nosmt [X86]
 
 	mminit_loglevel=
 			[KNL] When CONFIG_DEBUG_MEMORY_INIT is set, this

diff --git a/arch/x86/kernel/cpu/bugs.c b/arch/x86/kernel/cpu/bugs.c
@@ -230,7 +230,7 @@ static const char * const mds_strings[] = {
 
 static void __init mds_select_mitigation(void)
 {
-	if (!boot_cpu_has_bug(X86_BUG_MDS)) {
+	if (!boot_cpu_has_bug(X86_BUG_MDS) || cpu_mitigations_off()) {
 		mds_mitigation = MDS_MITIGATION_OFF;
 		return;
 	}
@@ -241,7 +241,8 @@ static void __init mds_select_mitigation(void)
 
 		static_branch_enable(&mds_user_clear);
 
-		if (mds_nosmt && !boot_cpu_has(X86_BUG_MSBDS_ONLY))
+		if (!boot_cpu_has(X86_BUG_MSBDS_ONLY) &&
+		    (mds_nosmt || cpu_mitigations_auto_nosmt()))
 			cpu_smt_disable(false);
 	}