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 <jpoimboe@redhat.com>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Reviewed-by: Tyler Hicks <tyhicks@canonical.com>
Acked-by: Jiri Kosina <jkosina@suse.cz>

diff --git a/arch/x86/kernel/cpu/bugs.c b/arch/x86/kernel/cpu/bugs.c
index 3f934ffef8cf3221016eb7c99126103b34135ae9..22a14d4b68a2b9d92828649c6ba55ef51146bd4a 100644 (file)
--- a/arch/x86/kernel/cpu/bugs.c
+++ b/arch/x86/kernel/cpu/bugs.c
@@ -673,6 +673,9 @@ static void update_indir_branch_cond(void)
                static_branch_disable(&switch_to_cond_stibp);
 }
 
+#undef pr_fmt
+#define pr_fmt(fmt) fmt
+
 /* Update the static key controlling the MDS CPU buffer clear in idle */
 static void update_mds_branch_idle(void)
 {
@@ -693,6 +696,8 @@ 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. */
@@ -717,6 +722,8 @@ 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:
@@ -1149,6 +1156,7 @@ static int __init l1tf_cmdline(char *str)
 early_param("l1tf", l1tf_cmdline);
 
 #undef pr_fmt
+#define pr_fmt(fmt) fmt
 
 #ifdef CONFIG_SYSFS