From e1a2cae2c00bb6ed091b10e44de50d2789c3f4b3 Mon Sep 17 00:00:00 2001
From: Dario Faggioli <dfaggioli@suse.com>
Date: Fri, 19 Apr 2019 14:30:10 +0200
Subject: [PATCH] L1TF/Linux: detect SMT via sysfs

We can figure out whether SMT is enabled or not, by checking the
topology of the CPUs, as it is exposed in /sys.

This means the information is available also when we are running
in `--sysfs-only` mode.
---
 spectre-meltdown-checker.sh | 25 +++++++++++++++++--------
 1 file changed, 17 insertions(+), 8 deletions(-)

diff --git a/spectre-meltdown-checker.sh b/spectre-meltdown-checker.sh
index dc5f10a..d158cfa 100755
--- a/spectre-meltdown-checker.sh
+++ b/spectre-meltdown-checker.sh
@@ -3932,16 +3932,25 @@ check_CVE_2018_3646_linux()
 	fi
 
 	smt_enabled=-1
-	if [ "$opt_sysfs_only" != 1 ]; then
-		_info_nol "  * Hyper-Threading (SMT) is enabled: "
-		is_cpu_smt_enabled; smt_enabled=$?
-		if [ "$smt_enabled" = 0 ]; then
-			pstatus yellow YES
-		elif [ "$smt_enabled" = 1 ]; then
-			pstatus green NO
+	_info_nol "  * Hyper-Threading (SMT) is enabled: "
+	if [ "$opt_sysfs_only" = 1 ]; then
+		# if SMT is on, `siblings_list` has more than one element,
+		# separated by ','. Also, it is safe enough to assume that
+		# cpu0 (1) always exists, and (2) is always online.
+		if ! grep -q ',' /sys/devices/system/cpu/cpu0/topology/thread_siblings_list ; then
+			smt_enabled=1 # means disabled!
 		else
-			pstatus yellow UNKNOWN
+			smt_enabled=0
 		fi
+	else
+		is_cpu_smt_enabled; smt_enabled=$?
+	fi
+	if [ "$smt_enabled" = 0 ]; then
+		pstatus yellow YES
+	elif [ "$smt_enabled" = 1 ]; then
+		pstatus green NO
+	else
+		pstatus yellow UNKNOWN
 	fi
 
 	if ! is_cpu_vulnerable "$cve"; then