Re: [Qemu-devel] [PATCH v2 11/19] s390x: allow only 1 CPU with TCG

[Matthew Rosato <mjrosato@linux.vnet.ibm.com>]

On 09/04/2017 11:43 AM, David Hildenbrand wrote:
> Specifying more than 1 CPU (e.g. -smp 5) leads to SIGP errors (the
> guest tries to bring these CPUs up but fails), because we don't support
> multiple CPUs on s390x under TCG.
> 
> Let's bail out if more than 1 is specified, so we don't raise people's
> hope. Make it a define, so we can easily bump it up later.
> 
> Signed-off-by: David Hildenbrand <david@redhat.com>
> ---

Makes sense.  Ran the described environment without this patch (errors)
and again with this patch (graceful exit w/ message).

Tested-by: Matthew Rosato <mjrosato@linux.vnet.ibm.com>

>  hw/s390x/s390-virtio-ccw.c | 7 +++++++
>  target/s390x/cpu.h         | 2 ++
>  2 files changed, 9 insertions(+)
> 
> diff --git a/hw/s390x/s390-virtio-ccw.c b/hw/s390x/s390-virtio-ccw.c
> index f67b4b5d58..f7ca20d77a 100644
> --- a/hw/s390x/s390-virtio-ccw.c
> +++ b/hw/s390x/s390-virtio-ccw.c
> @@ -23,6 +23,7 @@
>  #include "hw/s390x/css.h"
>  #include "virtio-ccw.h"
>  #include "qemu/config-file.h"
> +#include "qemu/error-report.h"
>  #include "s390-pci-bus.h"
>  #include "hw/s390x/storage-keys.h"
>  #include "hw/s390x/storage-attributes.h"
> @@ -55,6 +56,12 @@ static void s390_init_cpus(MachineState *machine)
>      if (machine->cpu_model == NULL) {
>          machine->cpu_model = s390_default_cpu_model_name();
>      }
> +    if (tcg_enabled() && max_cpus > S390_TCG_MAX_CPUS) {
> +        error_report("Number of SMP CPUs requested (%d) exceeds max CPUs "
> +                     "supported by TCG (%d) on s390x", max_cpus,
> +                     S390_TCG_MAX_CPUS);
> +        exit(1);
> +    }
> 
>      cpu_states = g_new0(S390CPU *, max_cpus);
> 
> diff --git a/target/s390x/cpu.h b/target/s390x/cpu.h
> index 147aceba28..dca6aa9aae 100644
> --- a/target/s390x/cpu.h
> +++ b/target/s390x/cpu.h
> @@ -209,6 +209,8 @@ static inline S390CPU *s390_env_get_cpu(CPUS390XState *env)
> 
>  #define ENV_OFFSET offsetof(S390CPU, env)
> 
> +#define S390_TCG_MAX_CPUS 1
> +
>  #ifndef CONFIG_USER_ONLY
>  extern const struct VMStateDescription vmstate_s390_cpu;
>  #endif
>