Re: [Qemu-devel] [PATCH] ppc: add helpful message when KVM fails to start VCPU

[Paolo Bonzini <pbonzini@redhat.com>]

On 18/05/2015 21:06, Laurent Vivier wrote:
> On POWER8 systems, KVM checks if VCPU is running on primary threads,
> and that secondary threads are offline. If this is not the case,
> ioctl() fails with errno set to EBUSY.
> 
> QEMU aborts with a non explicit error message:
> $ ./qemu-system-ppc64 --nographic -machine pseries,accel=kvm
> error: kvm run failed Device or resource busy
> 
> To help user to diagnose the problem, this patch adds an informative
> error message.
> 
> There is no easy way to check if SMT is enabled before starting the VCPU,
> and as this case is the only one setting errno to EBUSY, we just check
> the errno value to display a message.
> 
> Signed-off-by: Laurent Vivier <lvivier@redhat.com>

Thanks, applied to my queue for 2.4.

Paolo

> ---
>  kvm-all.c | 8 ++++++++
>  1 file changed, 8 insertions(+)
> 
> diff --git a/kvm-all.c b/kvm-all.c
> index 17a3771..7b57826 100644
> --- a/kvm-all.c
> +++ b/kvm-all.c
> @@ -1828,6 +1828,14 @@ int kvm_cpu_exec(CPUState *cpu)
>              }
>              fprintf(stderr, "error: kvm run failed %s\n",
>                      strerror(-run_ret));
> +#ifdef TARGET_PPC
> +            if (run_ret == -EBUSY) {
> +                fprintf(stderr,
> +                        "This is probably because your SMT is enabled.\n"
> +                        "VCPU can only run on primary threads with all "
> +                        "secondary threads offline.\n");
> +            }
> +#endif
>              ret = -1;
>              break;
>          }
>