fix: xen: consider Xen dom0 as non-guest (#343 continued)

(cherry picked from commit bc00a81526)

src/libs/360_cpu_smt.sh

@@ -46,8 +46,18 @@ is_arm_cpu() {
 # Check whether SMT (HyperThreading) is enabled on the system
 # Returns: 0 if SMT enabled, 1 otherwise
 is_cpu_smt_enabled() {
-    local siblings cpucores
-    # SMT / HyperThreading is enabled if siblings != cpucores
+    local siblings cpucores smt_active
+    # Most reliable: /sys/devices/system/cpu/smt/active mirrors the kernel's
+    # sched_smt_active() (1=SMT active, 0=not), which is exactly what the kernel
+    # itself uses to derive the "SMT (disabled|vulnerable)" vulnerability strings.
+    if [ -r /sys/devices/system/cpu/smt/active ]; then
+        smt_active=$(cat /sys/devices/system/cpu/smt/active 2>/dev/null)
+        case "$smt_active" in
+            1) return 0 ;;
+            0) return 1 ;;
+        esac
+    fi
+    # Fallback: SMT / HyperThreading is enabled if siblings != cpucores
     if [ -e "$g_procfs/cpuinfo" ]; then
         siblings=$(awk '/^siblings/  {print $3;exit}' "$g_procfs/cpuinfo")
         cpucores=$(awk '/^cpu cores/ {print $4;exit}' "$g_procfs/cpuinfo")

src/libs/370_hw_vmm.sh

@@ -127,7 +127,14 @@ is_running_as_guest() {
     if [ "${g_is_guest_vm_cached:-0}" != 1 ]; then
         g_is_guest_vm=0
         g_is_guest_vm_reason=''
-        if [ -e "$g_procfs/cpuinfo" ] && grep -qw 'hypervisor' "$g_procfs/cpuinfo" 2>/dev/null; then
+        # A Xen dom0 runs on top of the hypervisor and therefore also has the
+        # 'hypervisor' CPUID flag set, but it's the privileged control domain:
+        # it has direct hardware access and a truthful view of the host CPU
+        # topology, so it must not be classified as a guest (#343). Check it
+        # before the cpuinfo probe below, which would otherwise match.
+        if is_xen_dom0; then
+            g_is_guest_vm=0
+        elif [ -e "$g_procfs/cpuinfo" ] && grep -qw 'hypervisor' "$g_procfs/cpuinfo" 2>/dev/null; then
             g_is_guest_vm=1
             g_is_guest_vm_reason="'hypervisor' flag in $g_procfs/cpuinfo"
         fi