[PATCH v2] s390x/tcg: Implement MONITOR CALL

[David Hildenbrand <david@redhat.com>]

Recent upstream Linux uses the MONITOR CALL instruction for things like
BUG_ON() and WARN_ON(). We currently inject an operation exception when
we hit a MONITOR CALL instruction - which is wrong, as the instruction
is not glued to specific CPU features.

Doing a simple WARN_ON_ONCE() currently results in a panic:
  [   18.162801] illegal operation: 0001 ilc:2 [#1] SMP
  [   18.162889] Modules linked in:
  [...]
  [   18.165476] Kernel panic - not syncing: Fatal exception: panic_on_oops

With a proper implementation, we now get:
  [   18.242754] ------------[ cut here ]------------
  [   18.242855] WARNING: CPU: 7 PID: 1 at init/main.c:1534 [...]
  [   18.242919] Modules linked in:
  [...]
  [   18.246262] ---[ end trace a420477d71dc97b4 ]---
  [   18.259014] Freeing unused kernel memory: 4220K

Reported-by: Christian Borntraeger <borntraeger@de.ibm.com>
Signed-off-by: David Hildenbrand <david@redhat.com>
---

v1 -> v2:
-  Simplify by not using the tb flags, always calling the helper.

I looked into monitor-event counting, which looks easy at first glance
- but proper DAT/access exception handling is tricky. Leaving that for
a cold winter evening :)

---
 target/s390x/excp_helper.c | 23 +++++++++++++++++++++++
 target/s390x/helper.h      |  1 +
 target/s390x/insn-data.def |  3 +++
 target/s390x/translate.c   | 21 +++++++++++++++++++++
 4 files changed, 48 insertions(+)

diff --git a/target/s390x/excp_helper.c b/target/s390x/excp_helper.c
index 3b58d10df3..0adfbbda27 100644
--- a/target/s390x/excp_helper.c
+++ b/target/s390x/excp_helper.c
@@ -610,4 +610,27 @@ void s390x_cpu_do_unaligned_access(CPUState *cs, vaddr addr,
     tcg_s390_program_interrupt(env, PGM_SPECIFICATION, retaddr);
 }
 
+static void QEMU_NORETURN monitor_event(CPUS390XState *env,
+                                        uint64_t monitor_code,
+                                        uint8_t monitor_class, uintptr_t ra)
+{
+    /* Store the Monitor Code and the Monitor Class Number into the lowcore */
+    stq_phys(env_cpu(env)->as,
+             env->psa + offsetof(LowCore, monitor_code), monitor_code);
+    stw_phys(env_cpu(env)->as,
+             env->psa + offsetof(LowCore, mon_class_num), monitor_class);
+
+    tcg_s390_program_interrupt(env, PGM_MONITOR, ra);
+}
+
+void HELPER(monitor_call)(CPUS390XState *env, uint64_t monitor_code,
+                          uint32_t monitor_class)
+{
+    g_assert(monitor_class <= 0xff);
+
+    if (env->cregs[8] & (0x8000 >> monitor_class)) {
+        monitor_event(env, monitor_code, monitor_class, GETPC());
+    }
+}
+
 #endif /* CONFIG_USER_ONLY */
diff --git a/target/s390x/helper.h b/target/s390x/helper.h
index b7887b552b..55bd1551e6 100644
--- a/target/s390x/helper.h
+++ b/target/s390x/helper.h
@@ -349,4 +349,5 @@ DEF_HELPER_3(sic, void, env, i64, i64)
 DEF_HELPER_3(rpcit, void, env, i32, i32)
 DEF_HELPER_5(pcistb, void, env, i32, i32, i64, i32)
 DEF_HELPER_4(mpcifc, void, env, i32, i64, i32)
+DEF_HELPER_3(monitor_call, void, env, i64, i32)
 #endif
diff --git a/target/s390x/insn-data.def b/target/s390x/insn-data.def
index d79ae9e3f1..e14cbd63fa 100644
--- a/target/s390x/insn-data.def
+++ b/target/s390x/insn-data.def
@@ -617,6 +617,9 @@
     C(0x9a00, LAM,     RS_a,  Z,   0, a2, 0, 0, lam, 0)
     C(0xeb9a, LAMY,    RSY_a, LD,  0, a2, 0, 0, lam, 0)
 
+/* MONITOR CALL */
+    C(0xaf00, MC,      SI,    Z,   la1, 0, 0, 0, mc, 0)
+
 /* MOVE */
     C(0xd200, MVC,     SS_a,  Z,   la1, a2, 0, 0, mvc, 0)
     C(0xe544, MVHHI,   SIL,   GIE, la1, i2, 0, m1_16, mov2, 0)
diff --git a/target/s390x/translate.c b/target/s390x/translate.c
index a777343821..90dc1740e7 100644
--- a/target/s390x/translate.c
+++ b/target/s390x/translate.c
@@ -3302,6 +3302,27 @@ static DisasJumpType op_lcbb(DisasContext *s, DisasOps *o)
     return DISAS_NEXT;
 }
 
+static DisasJumpType op_mc(DisasContext *s, DisasOps *o)
+{
+#if !defined(CONFIG_USER_ONLY)
+    TCGv_i32 i2;
+#endif
+    const uint16_t monitor_class = get_field(s, i2);
+
+    if (monitor_class & 0xff00) {
+        gen_program_exception(s, PGM_SPECIFICATION);
+        return DISAS_NORETURN;
+    }
+
+#if !defined(CONFIG_USER_ONLY)
+    i2 = tcg_const_i32(monitor_class);
+    gen_helper_monitor_call(cpu_env, o->addr1, i2);
+    tcg_temp_free_i32(i2);
+#endif
+    /* Defaults to a NOP. */
+    return DISAS_NEXT;
+}
+
 static DisasJumpType op_mov2(DisasContext *s, DisasOps *o)
 {
     o->out = o->in2;
-- 
2.26.2