Re: [qemu-s390x] [PATCH v2 07/18] s390x/tcg: tolerate wrong wakeups due to floating interrupts

[Cornelia Huck]

On Wed, 17 Jan 2018 18:40:36 +0100
David Hildenbrand <address@hidden> wrote:

> This is a prparation for floating interrupt support and only applies to

s/prparation/preparation/

(can fix while applying)

> MTTCG, single threaded TCG works just fine. If a floating interrupt wakes
> up a VCPU and the CPU thinks it can run (clearing cs->halted), at
> the point where the interrupt would be delivered, already another VCPU
> might have picked up the interrupt, resulting in a wakeup without an
> interrupt (executing wrong code).
> 
> It is wrong to let the VCPU continue to execute (the WAIT PSW). Instead,
> we have to put the VCPU back to sleep.
> 
> Signed-off-by: David Hildenbrand <address@hidden>
> ---
>  target/s390x/excp_helper.c | 5 +++++
>  1 file changed, 5 insertions(+)
> 
> diff --git a/target/s390x/excp_helper.c b/target/s390x/excp_helper.c
> index a18842ccbd..eeffb49f63 100644
> --- a/target/s390x/excp_helper.c
> +++ b/target/s390x/excp_helper.c
> @@ -503,6 +503,11 @@ bool s390_cpu_exec_interrupt(CPUState *cs, int 
> interrupt_request)
>              s390_cpu_do_interrupt(cs);
>              return true;
>          }
> +        if (env->psw.mask & PSW_MASK_WAIT) {
> +            /* Woken up because of a floating interrupt but it has already
> +             * been delivered. Go back to sleep. */
> +            cpu_interrupt(CPU(cpu), CPU_INTERRUPT_HALT);
> +        }
>      }
>      return false;
>  }