Re: [kvm-unit-tests PATCH v3 4/6] s390x: lib: don't forward PSW when handling exception in SIE

[Claudio Imbrenda <imbrenda@linux.ibm.com>]

On Thu,  1 Jun 2023 09:02:00 +0200
Nico Boehr <nrb@linux.ibm.com> wrote:

> When we're handling a pgm int in SIE, we want to return to the SIE
> cleanup after handling the exception. That's why we set pgm_old_psw to
> the sie_exit label in fixup_pgm_int.
> 
> On nullifing pgm ints, fixup_pgm_int will also forward the old PSW such
> that we don't cause an pgm int again.
> 
> However, when we want to return to the sie_exit label, this is not
> needed (since we've manually set pgm_old_psw). Instead, forwarding the
> PSW might cause us to skip an instruction or end up in the middle of an
> instruction.
> 
> So, let's just skip the rest of the fixup in case we're inside SIE.
> 
> Note that we're intentionally not fixing up the PSW in the guest; that's
> best left to the test at hand by registering their own psw fixup.
> 
> Signed-off-by: Nico Boehr <nrb@linux.ibm.com>

Reviewed-by: Claudio Imbrenda <imbrenda@linux.ibm.com>

> ---
>  lib/s390x/interrupt.c | 1 +
>  1 file changed, 1 insertion(+)
> 
> diff --git a/lib/s390x/interrupt.c b/lib/s390x/interrupt.c
> index d97b5a3a7e97..3f07068877ee 100644
> --- a/lib/s390x/interrupt.c
> +++ b/lib/s390x/interrupt.c
> @@ -145,6 +145,7 @@ static void fixup_pgm_int(struct stack_frame_int *stack)
>  	if (lowcore.pgm_old_psw.addr >= (uint64_t)&sie_entry &&
>  	    lowcore.pgm_old_psw.addr <= (uint64_t)&sie_exit) {
>  		lowcore.pgm_old_psw.addr = (uint64_t)&sie_exit;
> +		return;
>  	}
>  
>  	switch (lowcore.pgm_int_code) {