[MODERATED] [PATCH RFC 3/4] 3

From: Josh Poimboeuf <[email protected]>
Subject: [PATCH RFC 3/4] x86/speculation/mds: Add SMT warning message

MDS is vulnerable with SMT.  Make that clear with a one-time printk
whenever SMT first gets enabled.

Signed-off-by: Josh Poimboeuf <[email protected]>
---
 arch/x86/kernel/cpu/bugs.c | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/arch/x86/kernel/cpu/bugs.c b/arch/x86/kernel/cpu/bugs.c
index 9e20aef01d38..346f0f05879d 100644
--- a/arch/x86/kernel/cpu/bugs.c
+++ b/arch/x86/kernel/cpu/bugs.c
@@ -691,6 +691,8 @@ static void update_mds_branch_idle(void)
 		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"
+
 void arch_smt_update(void)
 {
 	/* Enhanced IBRS implies STIBP. No update required. */
@@ -715,6 +717,8 @@ void arch_smt_update(void)
 	switch(mds_mitigation) {
 	case MDS_MITIGATION_FULL:
 	case MDS_MITIGATION_VMWERV:
+		if (sched_smt_active() && !boot_cpu_has(X86_BUG_MSBDS_ONLY))
+			pr_warn_once(MDS_MSG_SMT);
 		update_mds_branch_idle();
 		break;
 	case MDS_MITIGATION_OFF:
-- 
2.17.2