Re: [Qemu-devel] [PATCH v1 for-2.11 2/3] s390x/tcg: fix DIAG 308 with > 1 VCPU (single threaded TCG)

["Alex Bennée" <alex.bennee@linaro.org>]

David Hildenbrand <david@redhat.com> writes:

> Currently, single threaded TCG with > 1 VCPU gets stuck during IPL, when
> the bios tries to switch to the loaded kernel via DIAG 308.
>
> pause_all_vcpus()/resume_all_vcpus() should not be called from a VCPU.
>
> And there is also no need for it. run_on_cpu() will make sure that the
> CPUs exit KVM/TCG, where they get stopped. Once stopped, they will no
> longer run.
>
> Signed-off-by: David Hildenbrand <david@redhat.com>
> ---
>  target/s390x/diag.c | 4 ----
>  1 file changed, 4 deletions(-)
>
> diff --git a/target/s390x/diag.c b/target/s390x/diag.c
> index dbbb9e886f..52bc348808 100644
> --- a/target/s390x/diag.c
> +++ b/target/s390x/diag.c
> @@ -27,7 +27,6 @@ static int modified_clear_reset(S390CPU *cpu)
>      S390CPUClass *scc = S390_CPU_GET_CLASS(cpu);
>      CPUState *t;
>
> -    pause_all_vcpus();
>      cpu_synchronize_all_states();
>      CPU_FOREACH(t) {
>          run_on_cpu(t, s390_do_cpu_full_reset, RUN_ON_CPU_NULL);

I think you also need to fix the run_on_cpu to be a async_run_on_cpu as
you would otherwise hang waiting for run_on_cpu to finish on a
single-threaded TCG run (as you are in the only vCPU context).

If it is important that the source vCPU doesn't continue you can
schedule it's work afterwards with a async_safe_run_on_cpu which will
complete after all other vCPUs have executed their work.


> @@ -37,7 +36,6 @@ static int modified_clear_reset(S390CPU *cpu)
>      s390_crypto_reset();
>      scc->load_normal(CPU(cpu));
>      cpu_synchronize_all_post_reset();
> -    resume_all_vcpus();
>      return 0;
>  }
>
> @@ -53,7 +51,6 @@ static int load_normal_reset(S390CPU *cpu)
>      S390CPUClass *scc = S390_CPU_GET_CLASS(cpu);
>      CPUState *t;
>
> -    pause_all_vcpus();
>      cpu_synchronize_all_states();
>      CPU_FOREACH(t) {
>          run_on_cpu(t, s390_do_cpu_reset, RUN_ON_CPU_NULL);
> @@ -63,7 +60,6 @@ static int load_normal_reset(S390CPU *cpu)
>      scc->initial_cpu_reset(CPU(cpu));
>      scc->load_normal(CPU(cpu));
>      cpu_synchronize_all_post_reset();
> -    resume_all_vcpus();
>      return 0;
>  }
>
> --
> 2.13.6


--
Alex Bennée