target/s390x: Make MC raise specification exception when class >= 16

MC requires bit positions 8-11 (upper 4 bits of class) to be zeros,
otherwise it must raise a specification exception.

Cc: qemu-stable@nongnu.org
Fixes: 20d143e ("s390x/tcg: Implement MONITOR CALL")
Reviewed-by: David Hildenbrand <david@redhat.com>
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Signed-off-by: Ilya Leoshkevich <iii@linux.ibm.com>
Message-Id: <20230724082032.66864-6-iii@linux.ibm.com>
Signed-off-by: Thomas Huth <thuth@redhat.com>
(cherry picked from commit 9c028c0)
Signed-off-by: Michael Tokarev <mjt@tls.msk.ru>

target/s390x/tcg/excp_helper.c

@@ -639,7 +639,7 @@ void monitor_event(CPUS390XState *env,
 void HELPER(monitor_call)(CPUS390XState *env, uint64_t monitor_code,
                           uint32_t monitor_class)
 {
-    g_assert(monitor_class <= 0xff);
+    g_assert(monitor_class <= 0xf);
 
     if (env->cregs[8] & (0x8000 >> monitor_class)) {
         monitor_event(env, monitor_code, monitor_class, GETPC());

target/s390x/tcg/translate.c

@@ -3192,9 +3192,9 @@ static DisasJumpType op_lcbb(DisasContext *s, DisasOps *o)
 
 static DisasJumpType op_mc(DisasContext *s, DisasOps *o)
 {
-    const uint16_t monitor_class = get_field(s, i2);
+    const uint8_t monitor_class = get_field(s, i2);
 
-    if (monitor_class & 0xff00) {
+    if (monitor_class & 0xf0) {
         gen_program_exception(s, PGM_SPECIFICATION);
         return DISAS_NORETURN;
     }