5.18.5-rc1 review

@@ -443,5 +443,6 @@
 #define X86_BUG_TAA			X86_BUG(22) /* CPU is affected by TSX Async Abort(TAA) */
 #define X86_BUG_ITLB_MULTIHIT		X86_BUG(23) /* CPU may incur MCE during certain page attribute changes */
 #define X86_BUG_SRBDS			X86_BUG(24) /* CPU may leak RNG bits if not mitigated */
+#define X86_BUG_MMIO_STALE_DATA		X86_BUG(25) /* CPU is affected by Processor MMIO Stale Data vulnerabilities */
 
 #endif /* _ASM_X86_CPUFEATURES_H */

@@ -114,6 +114,25 @@
 						 * Not susceptible to
 						 * TSX Async Abort (TAA) vulnerabilities.
 						 */
+#define ARCH_CAP_SBDR_SSDP_NO		BIT(13)	/*
+						 * Not susceptible to SBDR and SSDP
+						 * variants of Processor MMIO stale data
+						 * vulnerabilities.
+						 */
+#define ARCH_CAP_FBSDP_NO		BIT(14)	/*
+						 * Not susceptible to FBSDP variant of
+						 * Processor MMIO stale data
+						 * vulnerabilities.
+						 */
+#define ARCH_CAP_PSDP_NO		BIT(15)	/*
+						 * Not susceptible to PSDP variant of
+						 * Processor MMIO stale data
+						 * vulnerabilities.
+						 */
+#define ARCH_CAP_FB_CLEAR		BIT(17)	/*
+						 * VERW clears CPU fill buffer
+						 * even on MDS_NO CPUs.
+						 */
 
 #define MSR_IA32_FLUSH_CMD		0x0000010b
 #define L1D_FLUSH			BIT(0)	/*

71 lines not on this page · raw message

@@ -443,5 +443,6 @@
 #define X86_BUG_TAA			X86_BUG(22) /* CPU is affected by TSX Async Abort(TAA) */
 #define X86_BUG_ITLB_MULTIHIT		X86_BUG(23) /* CPU may incur MCE during certain page attribute changes */
 #define X86_BUG_SRBDS			X86_BUG(24) /* CPU may leak RNG bits if not mitigated */
+#define X86_BUG_MMIO_STALE_DATA		X86_BUG(25) /* CPU is affected by Processor MMIO Stale Data vulnerabilities */
 
 #endif /* _ASM_X86_CPUFEATURES_H */

@@ -114,6 +114,25 @@
 						 * Not susceptible to
 						 * TSX Async Abort (TAA) vulnerabilities.
 						 */
+#define ARCH_CAP_SBDR_SSDP_NO		BIT(13)	/*
+						 * Not susceptible to SBDR and SSDP
+						 * variants of Processor MMIO stale data
+						 * vulnerabilities.
+						 */
+#define ARCH_CAP_FBSDP_NO		BIT(14)	/*
+						 * Not susceptible to FBSDP variant of
+						 * Processor MMIO stale data
+						 * vulnerabilities.
+						 */
+#define ARCH_CAP_PSDP_NO		BIT(15)	/*
+						 * Not susceptible to PSDP variant of
+						 * Processor MMIO stale data
+						 * vulnerabilities.
+						 */
+#define ARCH_CAP_FB_CLEAR		BIT(17)	/*
+						 * VERW clears CPU fill buffer
+						 * even on MDS_NO CPUs.
+						 */
 
 #define MSR_IA32_FLUSH_CMD		0x0000010b
 #define L1D_FLUSH			BIT(0)	/*

@@ -41,7 +41,7 @@ static void __init spectre_v2_select_mit
 static void __init ssb_select_mitigation(void);
 static void __init l1tf_select_mitigation(void);
 static void __init mds_select_mitigation(void);
-static void __init mds_print_mitigation(void);
+static void __init md_clear_update_mitigation(void);
 static void __init taa_select_mitigation(void);
 static void __init srbds_select_mitigation(void);
 static void __init l1d_flush_select_mitigation(void);

@@ -123,10 +123,10 @@ void __init check_bugs(void)
 	l1d_flush_select_mitigation();
 
 	/*
-	 * As MDS and TAA mitigations are inter-related, print MDS
-	 * mitigation until after TAA mitigation selection is done.
+	 * As MDS and TAA mitigations are inter-related, update and print their
+	 * mitigation after TAA mitigation selection is done.
 	 */
-	mds_print_mitigation();
+	md_clear_update_mitigation();
 
 	arch_smt_update();
 

@@ -267,14 +267,6 @@ static void __init mds_select_mitigation
 	}
 }
 
-static void __init mds_print_mitigation(void)
-{
-	if (!boot_cpu_has_bug(X86_BUG_MDS) || cpu_mitigations_off())
-		return;
-
-	pr_info("%s\n", mds_strings[mds_mitigation]);
-}
-
 static int __init mds_cmdline(char *str)
 {
 	if (!boot_cpu_has_bug(X86_BUG_MDS))

@@ -329,7 +321,7 @@ static void __init taa_select_mitigation
 	/* TSX previously disabled by tsx=off */
 	if (!boot_cpu_has(X86_FEATURE_RTM)) {
 		taa_mitigation = TAA_MITIGATION_TSX_DISABLED;
-		goto out;
+		return;
 	}
 
 	if (cpu_mitigations_off()) {

@@ -343,7 +335,7 @@ static void __init taa_select_mitigation
 	 */
 	if (taa_mitigation == TAA_MITIGATION_OFF &&
 	    mds_mitigation == MDS_MITIGATION_OFF)
-		goto out;
+		return;
 
 	if (boot_cpu_has(X86_FEATURE_MD_CLEAR))
 		taa_mitigation = TAA_MITIGATION_VERW;

@@ -375,18 +367,6 @@ static void __init taa_select_mitigation
 
 	if (taa_nosmt || cpu_mitigations_auto_nosmt())
 		cpu_smt_disable(false);
-
-	/*
-	 * Update MDS mitigation, if necessary, as the mds_user_clear is
-	 * now enabled for TAA mitigation.
-	 */
-	if (mds_mitigation == MDS_MITIGATION_OFF &&
-	    boot_cpu_has_bug(X86_BUG_MDS)) {
-		mds_mitigation = MDS_MITIGATION_FULL;
-		mds_select_mitigation();
-	}
-out:
-	pr_info("%s\n", taa_strings[taa_mitigation]);
 }
 
 static int __init tsx_async_abort_parse_cmdline(char *str)

@@ -411,6 +391,33 @@ static int __init tsx_async_abort_parse_
 early_param("tsx_async_abort", tsx_async_abort_parse_cmdline);
 
 #undef pr_fmt
+#define pr_fmt(fmt)     "" fmt
+
+static void __init md_clear_update_mitigation(void)
+{
+	if (cpu_mitigations_off())
+		return;
+
+	if (!static_key_enabled(&mds_user_clear))
+		goto out;
+
+	/*
+	 * mds_user_clear is now enabled. Update MDS mitigation, if
+	 * necessary.
+	 */
+	if (mds_mitigation == MDS_MITIGATION_OFF &&
+	    boot_cpu_has_bug(X86_BUG_MDS)) {
+		mds_mitigation = MDS_MITIGATION_FULL;
+		mds_select_mitigation();
+	}
+out:
+	if (boot_cpu_has_bug(X86_BUG_MDS))
+		pr_info("MDS: %s\n", mds_strings[mds_mitigation]);
+	if (boot_cpu_has_bug(X86_BUG_TAA))
+		pr_info("TAA: %s\n", taa_strings[taa_mitigation]);
+}
+
+#undef pr_fmt
 #define pr_fmt(fmt)	"SRBDS: " fmt
 
 enum srbds_mitigations {

@@ -269,6 +269,8 @@ DECLARE_STATIC_KEY_FALSE(mds_idle_clear)
 
 DECLARE_STATIC_KEY_FALSE(switch_mm_cond_l1d_flush);
 
+DECLARE_STATIC_KEY_FALSE(mmio_stale_data_clear);
+
 #include <asm/segment.h>
 
 /**

156 lines not on this page · raw message

@@ -6773,6 +6773,9 @@ static noinstr void vmx_vcpu_enter_exit(
 		vmx_l1d_flush(vcpu);
 	else if (static_branch_unlikely(&mds_user_clear))
 		mds_clear_cpu_buffers();
+	else if (static_branch_unlikely(&mmio_stale_data_clear) &&
+		 kvm_arch_has_assigned_device(vcpu->kvm))
+		mds_clear_cpu_buffers();
 
 	if (vcpu->arch.cr2 != native_read_cr2())
 		native_write_cr2(vcpu->arch.cr2);

@@ -42,6 +42,7 @@ static void __init ssb_select_mitigation
 static void __init l1tf_select_mitigation(void);
 static void __init mds_select_mitigation(void);
 static void __init md_clear_update_mitigation(void);
+static void __init md_clear_select_mitigation(void);
 static void __init taa_select_mitigation(void);
 static void __init mmio_select_mitigation(void);
 static void __init srbds_select_mitigation(void);

@@ -122,19 +123,10 @@ void __init check_bugs(void)
 	spectre_v2_select_mitigation();
 	ssb_select_mitigation();
 	l1tf_select_mitigation();
-	mds_select_mitigation();
-	taa_select_mitigation();
-	mmio_select_mitigation();
+	md_clear_select_mitigation();
 	srbds_select_mitigation();
 	l1d_flush_select_mitigation();
 
-	/*
-	 * As MDS, TAA and MMIO Stale Data mitigations are inter-related, update
-	 * and print their mitigation after MDS, TAA and MMIO Stale Data
-	 * mitigation selection is done.
-	 */
-	md_clear_update_mitigation();
-
 	arch_smt_update();
 
 #ifdef CONFIG_X86_32

@@ -520,6 +512,20 @@ out:
 		pr_info("MMIO Stale Data: %s\n", mmio_strings[mmio_mitigation]);
 }
 
+static void __init md_clear_select_mitigation(void)
+{
+	mds_select_mitigation();
+	taa_select_mitigation();
+	mmio_select_mitigation();
+
+	/*
+	 * As MDS, TAA and MMIO Stale Data mitigations are inter-related, update
+	 * and print their mitigation after MDS, TAA and MMIO Stale Data
+	 * mitigation selection is done.
+	 */
+	md_clear_update_mitigation();
+}
+
 #undef pr_fmt
 #define pr_fmt(fmt)	"SRBDS: " fmt
 

@@ -434,6 +434,14 @@ static void __init mmio_select_mitigatio
 		static_branch_enable(&mmio_stale_data_clear);
 
 	/*
+	 * If Processor-MMIO-Stale-Data bug is present and Fill Buffer data can
+	 * be propagated to uncore buffers, clearing the Fill buffers on idle
+	 * is required irrespective of SMT state.
+	 */
+	if (!(ia32_cap & ARCH_CAP_FBSDP_NO))
+		static_branch_enable(&mds_idle_clear);
+
+	/*
 	 * Check if the system has the right microcode.
 	 *
 	 * CPU Fill buffer clear mitigation is enumerated by either an explicit

@@ -1225,6 +1233,8 @@ static void update_indir_branch_cond(voi
 /* Update the static key controlling the MDS CPU buffer clear in idle */
 static void update_mds_branch_idle(void)
 {
+	u64 ia32_cap = x86_read_arch_cap_msr();
+
 	/*
 	 * Enable the idle clearing if SMT is active on CPUs which are
 	 * affected only by MSBDS and not any other MDS variant.

@@ -1236,10 +1246,12 @@ static void update_mds_branch_idle(void)
 	if (!boot_cpu_has_bug(X86_BUG_MSBDS_ONLY))
 		return;
 
-	if (sched_smt_active())
+	if (sched_smt_active()) {
 		static_branch_enable(&mds_idle_clear);
-	else
+	} else if (mmio_mitigation == MMIO_MITIGATION_OFF ||
+		   (ia32_cap & ARCH_CAP_FBSDP_NO)) {
 		static_branch_disable(&mds_idle_clear);
+	}
 }
 
 #define MDS_MSG_SMT "MDS CPU bug present and SMT on, data leak possible. See https://www.kernel.org/doc/html/latest/admin-guide/hw-vuln/mds.html for more details.\n"

@@ -1902,6 +1902,20 @@ static ssize_t tsx_async_abort_show_stat
 		       sched_smt_active() ? "vulnerable" : "disabled");
 }
 
+static ssize_t mmio_stale_data_show_state(char *buf)
+{
+	if (mmio_mitigation == MMIO_MITIGATION_OFF)
+		return sysfs_emit(buf, "%s\n", mmio_strings[mmio_mitigation]);
+
+	if (boot_cpu_has(X86_FEATURE_HYPERVISOR)) {
+		return sysfs_emit(buf, "%s; SMT Host state unknown\n",
+				  mmio_strings[mmio_mitigation]);
+	}
+
+	return sysfs_emit(buf, "%s; SMT %s\n", mmio_strings[mmio_mitigation],
+			  sched_smt_active() ? "vulnerable" : "disabled");
+}
+
 static char *stibp_state(void)
 {
 	if (spectre_v2_in_eibrs_mode(spectre_v2_enabled))

@@ -2002,6 +2016,9 @@ static ssize_t cpu_show_common(struct de
 	case X86_BUG_SRBDS:
 		return srbds_show_state(buf);
 
+	case X86_BUG_MMIO_STALE_DATA:
+		return mmio_stale_data_show_state(buf);
+
 	default:
 		break;
 	}

@@ -2053,4 +2070,9 @@ ssize_t cpu_show_srbds(struct device *de
 {
 	return cpu_show_common(dev, attr, buf, X86_BUG_SRBDS);
 }
+
+ssize_t cpu_show_mmio_stale_data(struct device *dev, struct device_attribute *attr, char *buf)
+{
+	return cpu_show_common(dev, attr, buf, X86_BUG_MMIO_STALE_DATA);
+}
 #endif

@@ -564,6 +564,12 @@ ssize_t __weak cpu_show_srbds(struct dev
 	return sysfs_emit(buf, "Not affected\n");
 }
 
+ssize_t __weak cpu_show_mmio_stale_data(struct device *dev,
+					struct device_attribute *attr, char *buf)
+{
+	return sysfs_emit(buf, "Not affected\n");
+}
+
 static DEVICE_ATTR(meltdown, 0444, cpu_show_meltdown, NULL);
 static DEVICE_ATTR(spectre_v1, 0444, cpu_show_spectre_v1, NULL);
 static DEVICE_ATTR(spectre_v2, 0444, cpu_show_spectre_v2, NULL);

@@ -573,6 +579,7 @@ static DEVICE_ATTR(mds, 0444, cpu_show_m
 static DEVICE_ATTR(tsx_async_abort, 0444, cpu_show_tsx_async_abort, NULL);
 static DEVICE_ATTR(itlb_multihit, 0444, cpu_show_itlb_multihit, NULL);
 static DEVICE_ATTR(srbds, 0444, cpu_show_srbds, NULL);
+static DEVICE_ATTR(mmio_stale_data, 0444, cpu_show_mmio_stale_data, NULL);
 
 static struct attribute *cpu_root_vulnerabilities_attrs[] = {
 	&dev_attr_meltdown.attr,

@@ -584,6 +591,7 @@ static struct attribute *cpu_root_vulner
 	&dev_attr_tsx_async_abort.attr,
 	&dev_attr_itlb_multihit.attr,
 	&dev_attr_srbds.attr,
+	&dev_attr_mmio_stale_data.attr,
 	NULL
 };
 

@@ -65,6 +65,9 @@ extern ssize_t cpu_show_tsx_async_abort(
 extern ssize_t cpu_show_itlb_multihit(struct device *dev,
 				      struct device_attribute *attr, char *buf);
 extern ssize_t cpu_show_srbds(struct device *dev, struct device_attribute *attr, char *buf);
+extern ssize_t cpu_show_mmio_stale_data(struct device *dev,
+					struct device_attribute *attr,
+					char *buf);
 
 extern __printf(4, 5)
 struct device *cpu_device_create(struct device *parent, void *drvdata,

@@ -595,11 +595,13 @@ static void __init srbds_select_mitigati
 		return;
 
 	/*
-	 * Check to see if this is one of the MDS_NO systems supporting
-	 * TSX that are only exposed to SRBDS when TSX is enabled.
+	 * Check to see if this is one of the MDS_NO systems supporting TSX that
+	 * are only exposed to SRBDS when TSX is enabled or when CPU is affected
+	 * by Processor MMIO Stale Data vulnerability.
 	 */
 	ia32_cap = x86_read_arch_cap_msr();
-	if ((ia32_cap & ARCH_CAP_MDS_NO) && !boot_cpu_has(X86_FEATURE_RTM))
+	if ((ia32_cap & ARCH_CAP_MDS_NO) && !boot_cpu_has(X86_FEATURE_RTM) &&
+	    !boot_cpu_has_bug(X86_BUG_MMIO_STALE_DATA))
 		srbds_mitigation = SRBDS_MITIGATION_TSX_OFF;
 	else if (boot_cpu_has(X86_FEATURE_HYPERVISOR))
 		srbds_mitigation = SRBDS_MITIGATION_HYPERVISOR;

@@ -1239,6 +1239,8 @@ static const __initconst struct x86_cpu_
 #define SRBDS		BIT(0)
 /* CPU is affected by X86_BUG_MMIO_STALE_DATA */
 #define MMIO		BIT(1)
+/* CPU is affected by Shared Buffers Data Sampling (SBDS), a variant of X86_BUG_MMIO_STALE_DATA */
+#define MMIO_SBDS	BIT(2)
 
 static const struct x86_cpu_id cpu_vuln_blacklist[] __initconst = {
 	VULNBL_INTEL_STEPPINGS(IVYBRIDGE,	X86_STEPPING_ANY,		SRBDS),

@@ -1260,16 +1262,17 @@ static const struct x86_cpu_id cpu_vuln_
 	VULNBL_INTEL_STEPPINGS(KABYLAKE_L,	X86_STEPPINGS(0x0, 0x8),	SRBDS),
 	VULNBL_INTEL_STEPPINGS(KABYLAKE,	X86_STEPPINGS(0x9, 0xD),	SRBDS | MMIO),
 	VULNBL_INTEL_STEPPINGS(KABYLAKE,	X86_STEPPINGS(0x0, 0x8),	SRBDS),
-	VULNBL_INTEL_STEPPINGS(ICELAKE_L,	X86_STEPPINGS(0x5, 0x5),	MMIO),
+	VULNBL_INTEL_STEPPINGS(ICELAKE_L,	X86_STEPPINGS(0x5, 0x5),	MMIO | MMIO_SBDS),
 	VULNBL_INTEL_STEPPINGS(ICELAKE_D,	X86_STEPPINGS(0x1, 0x1),	MMIO),
 	VULNBL_INTEL_STEPPINGS(ICELAKE_X,	X86_STEPPINGS(0x4, 0x6),	MMIO),
-	VULNBL_INTEL_STEPPINGS(COMETLAKE,	BIT(2) | BIT(3) | BIT(5),	MMIO),
-	VULNBL_INTEL_STEPPINGS(COMETLAKE_L,	X86_STEPPINGS(0x0, 0x1),	MMIO),
-	VULNBL_INTEL_STEPPINGS(LAKEFIELD,	X86_STEPPINGS(0x1, 0x1),	MMIO),
+	VULNBL_INTEL_STEPPINGS(COMETLAKE,	BIT(2) | BIT(3) | BIT(5),	MMIO | MMIO_SBDS),
+	VULNBL_INTEL_STEPPINGS(COMETLAKE_L,	X86_STEPPINGS(0x1, 0x1),	MMIO | MMIO_SBDS),
+	VULNBL_INTEL_STEPPINGS(COMETLAKE_L,	X86_STEPPINGS(0x0, 0x0),	MMIO),
+	VULNBL_INTEL_STEPPINGS(LAKEFIELD,	X86_STEPPINGS(0x1, 0x1),	MMIO | MMIO_SBDS),
 	VULNBL_INTEL_STEPPINGS(ROCKETLAKE,	X86_STEPPINGS(0x1, 0x1),	MMIO),
-	VULNBL_INTEL_STEPPINGS(ATOM_TREMONT,	X86_STEPPINGS(0x1, 0x1),	MMIO),
+	VULNBL_INTEL_STEPPINGS(ATOM_TREMONT,	X86_STEPPINGS(0x1, 0x1),	MMIO | MMIO_SBDS),
 	VULNBL_INTEL_STEPPINGS(ATOM_TREMONT_D,	X86_STEPPING_ANY,		MMIO),
-	VULNBL_INTEL_STEPPINGS(ATOM_TREMONT_L,	X86_STEPPINGS(0x0, 0x0),	MMIO),
+	VULNBL_INTEL_STEPPINGS(ATOM_TREMONT_L,	X86_STEPPINGS(0x0, 0x0),	MMIO | MMIO_SBDS),
 	{}
 };
 

@@ -1350,10 +1353,14 @@ static void __init cpu_set_bug_bits(stru
 	/*
 	 * SRBDS affects CPUs which support RDRAND or RDSEED and are listed
 	 * in the vulnerability blacklist.
+	 *
+	 * Some of the implications and mitigation of Shared Buffers Data
+	 * Sampling (SBDS) are similar to SRBDS. Give SBDS same treatment as
+	 * SRBDS.
 	 */
 	if ((cpu_has(c, X86_FEATURE_RDRAND) ||
 	     cpu_has(c, X86_FEATURE_RDSEED)) &&
-	    cpu_matches(cpu_vuln_blacklist, SRBDS))
+	    cpu_matches(cpu_vuln_blacklist, SRBDS | MMIO_SBDS))
 		    setup_force_cpu_bug(X86_BUG_SRBDS);
 
 	/*

@@ -133,6 +133,11 @@
 						 * VERW clears CPU fill buffer
 						 * even on MDS_NO CPUs.
 						 */
+#define ARCH_CAP_FB_CLEAR_CTRL		BIT(18)	/*
+						 * MSR_IA32_MCU_OPT_CTRL[FB_CLEAR_DIS]
+						 * bit available to control VERW
+						 * behavior.
+						 */
 
 #define MSR_IA32_FLUSH_CMD		0x0000010b
 #define L1D_FLUSH			BIT(0)	/*

@@ -150,6 +155,7 @@
 #define MSR_IA32_MCU_OPT_CTRL		0x00000123
 #define RNGDS_MITG_DIS			BIT(0)	/* SRBDS support */
 #define RTM_ALLOW			BIT(1)	/* TSX development mode */
+#define FB_CLEAR_DIS			BIT(3)	/* CPU Fill buffer clear disable */
 
 #define MSR_IA32_SYSENTER_CS		0x00000174
 #define MSR_IA32_SYSENTER_ESP		0x00000175

111 lines not on this page · raw message

@@ -348,6 +348,8 @@ struct vcpu_vmx {
 	u64 msr_ia32_feature_control_valid_bits;
 	/* SGX Launch Control public key hash */
 	u64 msr_ia32_sgxlepubkeyhash[4];
+	u64 msr_ia32_mcu_opt_ctrl;
+	bool disable_fb_clear;
 
 	struct pt_desc pt_desc;
 	struct lbr_desc lbr_desc;

@@ -1587,6 +1587,9 @@ static u64 kvm_get_arch_capabilities(voi
 		 */
 	}
 
+	/* Guests don't need to know "Fill buffer clear control" exists */
+	data &= ~ARCH_CAP_FB_CLEAR_CTRL;
+
 	return data;
 }
 

@@ -133,6 +133,11 @@
 						 * VERW clears CPU fill buffer
 						 * even on MDS_NO CPUs.
 						 */
+#define ARCH_CAP_FB_CLEAR_CTRL		BIT(18)	/*
+						 * MSR_IA32_MCU_OPT_CTRL[FB_CLEAR_DIS]
+						 * bit available to control VERW
+						 * behavior.
+						 */
 
 #define MSR_IA32_FLUSH_CMD		0x0000010b
 #define L1D_FLUSH			BIT(0)	/*

@@ -150,6 +155,7 @@
 #define MSR_IA32_MCU_OPT_CTRL		0x00000123
 #define RNGDS_MITG_DIS			BIT(0)	/* SRBDS support */
 #define RTM_ALLOW			BIT(1)	/* TSX development mode */
+#define FB_CLEAR_DIS			BIT(3)	/* CPU Fill buffer clear disable */
 
 #define MSR_IA32_SYSENTER_CS		0x00000174
 #define MSR_IA32_SYSENTER_ESP		0x00000175

@@ -1258,6 +1258,7 @@ static void update_mds_branch_idle(void)
 
 #define MDS_MSG_SMT "MDS CPU bug present and SMT on, data leak possible. See https://www.kernel.org/doc/html/latest/admin-guide/hw-vuln/mds.html for more details.\n"
 #define TAA_MSG_SMT "TAA CPU bug present and SMT on, data leak possible. See https://www.kernel.org/doc/html/latest/admin-guide/hw-vuln/tsx_async_abort.html for more details.\n"
+#define MMIO_MSG_SMT "MMIO Stale Data CPU bug present and SMT on, data leak possible. See https://www.kernel.org/doc/html/latest/admin-guide/hw-vuln/processor_mmio_stale_data.html for more details.\n"
 
 void cpu_bugs_smt_update(void)
 {

@@ -1302,6 +1303,16 @@ void cpu_bugs_smt_update(void)
 		break;
 	}
 
+	switch (mmio_mitigation) {
+	case MMIO_MITIGATION_VERW:
+	case MMIO_MITIGATION_UCODE_NEEDED:
+		if (sched_smt_active())
+			pr_warn_once(MMIO_MSG_SMT);
+		break;
+	case MMIO_MITIGATION_OFF:
+		break;
+	}
+
 	mutex_unlock(&spec_ctrl_mutex);
 }