[PATCH 3.16 78/86] x86/speculation/mds: Print SMT vulnerable on MSBDS with mitigations off

Ben Hutchings
2019-05-16T16:00:50Z

From: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>

commit e2c3c94788b08891dcf3dbe608f9880523ecd71b upstream.

This code is only for CPUs which are affected by MSBDS, but are *not*
affected by the other two MDS issues.

For such CPUs, enabling the mds_idle_clear mitigation is enough to
mitigate SMT.

However if user boots with 'mds=off' and still has SMT enabled, we should
not report that SMT is mitigated:

$cat /sys//devices/system/cpu/vulnerabilities/mds
Vulnerable; SMT mitigated

But rather:
Vulnerable; SMT vulnerable

Signed-off-by: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Reviewed-by: Tyler Hicks <tyhicks@canonical.com>
Reviewed-by: Josh Poimboeuf <jpoimboe@redhat.com>
Link: https://lkml.kernel.org/r/20190412215118.294906495@localhost.localdomain
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>
---
arch/x86/kernel/cpu/bugs.c | 3 ++-
1 file changed, 2 insertions(+), 1 deletion(-)

--- a/arch/x86/kernel/cpu/bugs.c
+++ b/arch/x86/kernel/cpu/bugs.c
@@ -1156,7 +1156,8 @@ static ssize_t mds_show_state(char *buf)

if (boot_cpu_has(X86_BUG_MSBDS_ONLY)) {
return sprintf(buf, "%s; SMT %s\n", mds_strings[mds_mitigation],
- sched_smt_active() ? "mitigated" : "disabled");
+ (mds_mitigation == MDS_MITIGATION_OFF ? "vulnerable" :
+ sched_smt_active() ? "mitigated" : "disabled"));
}

return sprintf(buf, "%s; SMT %s\n", mds_strings[mds_mitigation],