linux-kernel - [PATCH 2/2] x86/speculation: Print error when mitigations are disabled

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Date:   Thu, 15 Jun 2023 09:44:17 -0700
From:   Breno Leitao <leitao@...ian.org>
To:     pawan.kumar.gupta@...ux.intel.com, jpoimboe@...nel.org,
        peterz@...radead.org, tglx@...utronix.de, bp@...en8.de,
        Ingo Molnar <mingo@...hat.com>,
        Dave Hansen <dave.hansen@...ux.intel.com>, x86@...nel.org,
        "H. Peter Anvin" <hpa@...or.com>
Cc:     leit@...com, linux-kernel@...r.kernel.org
Subject: [PATCH 2/2] x86/speculation: Print error when mitigations are disabled

If mitigations are disabled for MDS, TAA, MMIO we want to let users
aware. This is either disabled by "mitigations=off" kernel argument, or,
by CONFIG_SPECULATION_MITIGATIONS=n

Signed-off-by: Breno Leitao <leitao@...ian.org>
---
 arch/x86/kernel/cpu/bugs.c | 19 ++++++++++++++++---
 1 file changed, 16 insertions(+), 3 deletions(-)

diff --git a/arch/x86/kernel/cpu/bugs.c b/arch/x86/kernel/cpu/bugs.c
index 703649a29181..b678cdd95dc1 100644
--- a/arch/x86/kernel/cpu/bugs.c
+++ b/arch/x86/kernel/cpu/bugs.c
@@ -275,6 +275,7 @@ static void x86_amd_ssb_disable(void)
 /* Default mitigation for MDS-affected CPUs */
 static enum mds_mitigations mds_mitigation __ro_after_init = MDS_MITIGATION_FULL;
 static bool mds_nosmt __ro_after_init = false;
+#define MDS_WARN_MSG "WARNING: Microarchitectural Data Sampling (MDS) speculative mitigation disabled!\n"
 
 static const char * const mds_strings[] = {
 	[MDS_MITIGATION_OFF]	= "Vulnerable",
@@ -284,11 +285,16 @@ static const char * const mds_strings[] = {
 
 static void __init mds_select_mitigation(void)
 {
-	if (!boot_cpu_has_bug(X86_BUG_MDS) || cpu_speculative_mitigations_off()) {
+	if (!boot_cpu_has_bug(X86_BUG_MDS)) {
 		mds_mitigation = MDS_MITIGATION_OFF;
 		return;
 	}
 
+	if (cpu_speculative_mitigations_off()) {
+		pr_err(MDS_WARN_MSG);
+		mds_mitigation = MDS_MITIGATION_OFF;
+	}
+
 	if (mds_mitigation == MDS_MITIGATION_FULL) {
 		if (!boot_cpu_has(X86_FEATURE_MD_CLEAR))
 			mds_mitigation = MDS_MITIGATION_VMWERV;
@@ -335,6 +341,7 @@ enum taa_mitigations {
 /* Default mitigation for TAA-affected CPUs */
 static enum taa_mitigations taa_mitigation __ro_after_init = TAA_MITIGATION_VERW;
 static bool taa_nosmt __ro_after_init;
+#define TAA_WARN_MSG "WARNING: TSX Asynchronous Abort (TAA) speculative mitigation disabled!\n"
 
 static const char * const taa_strings[] = {
 	[TAA_MITIGATION_OFF]		= "Vulnerable",
@@ -359,6 +366,7 @@ static void __init taa_select_mitigation(void)
 	}
 
 	if (cpu_speculative_mitigations_off()) {
+		pr_err(TAA_WARN_MSG);
 		taa_mitigation = TAA_MITIGATION_OFF;
 		return;
 	}
@@ -436,6 +444,7 @@ enum mmio_mitigations {
 /* Default mitigation for Processor MMIO Stale Data vulnerabilities */
 static enum mmio_mitigations mmio_mitigation __ro_after_init = MMIO_MITIGATION_VERW;
 static bool mmio_nosmt __ro_after_init = false;
+#define MMIO_WARN_MSG "WARNING: MMIO Stale Data speculative mitigation disabled!\n"
 
 static const char * const mmio_strings[] = {
 	[MMIO_MITIGATION_OFF]		= "Vulnerable",
@@ -448,12 +457,16 @@ static void __init mmio_select_mitigation(void)
 	u64 ia32_cap;
 
 	if (!boot_cpu_has_bug(X86_BUG_MMIO_STALE_DATA) ||
-	     boot_cpu_has_bug(X86_BUG_MMIO_UNKNOWN) ||
-	     cpu_speculative_mitigations_off()) {
+	     boot_cpu_has_bug(X86_BUG_MMIO_UNKNOWN)) {
 		mmio_mitigation = MMIO_MITIGATION_OFF;
 		return;
 	}
 
+	if (cpu_speculative_mitigations_off()) {
+		pr_err(MMIO_WARN_MSG);
+		mmio_mitigation = MMIO_MITIGATION_OFF;
+	}
+
 	if (mmio_mitigation == MMIO_MITIGATION_OFF)
 		return;
 
-- 
2.34.1