[PATCH v2] s390x/tcg: MVCL: Exit to main loop if requested

[David Hildenbrand <david@redhat.com>]

MVCL is interruptible and we should check for interrupts and process
them after writing back the variables to the registers. Let's check
for any exit requests and exit to the main loop.

When booting Fedora 30, I can see a handful of these exits and it seems
to work reliable. (it never get's triggered via EXECUTE, though)

Suggested-by: Richard Henderson <richard.henderson@linaro.org>
Signed-off-by: David Hildenbrand <david@redhat.com>
---

v1 -> v2:
- Check only if icount_decr.u32 < 0
- Drop should_interrupt_instruction() and perform the check inline
- Rephrase comment, subject, and description

---
 target/s390x/mem_helper.c | 10 +++++++++-
 1 file changed, 9 insertions(+), 1 deletion(-)

diff --git a/target/s390x/mem_helper.c b/target/s390x/mem_helper.c
index 4254548935..87e4ebd169 100644
--- a/target/s390x/mem_helper.c
+++ b/target/s390x/mem_helper.c
@@ -1015,6 +1015,7 @@ uint32_t HELPER(mvcl)(CPUS390XState *env, uint32_t r1, uint32_t r2)
     uint64_t srclen = env->regs[r2 + 1] & 0xffffff;
     uint64_t src = get_address(env, r2);
     uint8_t pad = env->regs[r2 + 1] >> 24;
+    CPUState *cs = env_cpu(env);
     S390Access srca, desta;
     uint32_t cc, cur_len;
 
@@ -1065,7 +1066,14 @@ uint32_t HELPER(mvcl)(CPUS390XState *env, uint32_t r1, uint32_t r2)
         env->regs[r1 + 1] = deposit64(env->regs[r1 + 1], 0, 24, destlen);
         set_address_zero(env, r1, dest);
 
-        /* TODO: Deliver interrupts. */
+        /*
+         * MVCL is interruptible. Check if somebody (e.g., cpu_interrupt() or
+         * cpu_exit()) asked us to return to the main loop. In case there is
+         * no deliverable interrupt, we'll end up back in this handler.
+         */
+        if (unlikely((int32_t)atomic_read(&cpu_neg(cs)->icount_decr.u32) < 0)) {
+            cpu_loop_exit_restore(cs, ra);
+        }
     }
     return cc;
 }
-- 
2.21.0