s390x/tcg: Implement MONITOR CALL

s390x/tcg: Implement MONITOR CALL

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 <[email protected]>
Signed-off-by: David Hildenbrand <[email protected]>
Reviewed-by: Richard Henderson <[email protected]>
Message-Id: <20200918085122[email protected]>
Signed-off-by: Cornelia Huck <[email protected]>