Re: [PATCH v2] s390x/tcg: Implement MONITOR CALL

[Cornelia Huck]

On Fri, 18 Sep 2020 10:51:22 +0200
David Hildenbrand <david@redhat.com> wrote:

> 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 :)

Fortunately, this is covered by a facility bit, so no need to do this
now :)

> 
> ---
>  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(+)

Thanks, applied.