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

commit 5c14068 upstream. Add MDS to the new 'mitigations=' cmdline option. Signed-off-by: Josh Poimboeuf <jpoimboe@redhat.com> Signed-off-by: Thomas Gleixner <tglx@linutronix.de> [bwh: Backported to 3.16: - Drop the auto,nosmt option, which we can't support - Adjust filenames, context] Signed-off-by: Ben Hutchings <ben@decadent.org.uk>
mariux64 · May 22, 2019 · 4265ee7 · 4265ee7
1 parent ac8b525
commit 4265ee7
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diff --git a/Documentation/kernel-parameters.txt b/Documentation/kernel-parameters.txt
@@ -1920,6 +1920,7 @@ bytes respectively. Such letter suffixes can also be entirely omitted.
 					       nospectre_v2 [X86]
 					       spectre_v2_user=off [X86]
 					       spec_store_bypass_disable=off [X86]
+					       mds=off [X86]
 
 			auto (default)
 				Mitigate all CPU vulnerabilities, but leave SMT

diff --git a/arch/x86/kernel/cpu/bugs.c b/arch/x86/kernel/cpu/bugs.c
@@ -287,7 +287,7 @@ 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;
 	}