[Qemu-devel] Re: [COMMIT 733318e] don't call cpu_sychronize_state from reset handlers

[Jan Kiszka <jan.kiszka@siemens.com>]

Anthony Liguori wrote:
> From: Glauber Costa <glommer-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org>
> 
> Doing this will make the vcpu ioctl be issued from the I/O thread, instead
> of cpu thread. The correct behaviour is to call it from within the cpu thread,
> as soon as we are ready to go.

Note that in the good old days, this used to work properly (in qemu-kvm)
as registers write-back was routed through on_vcpu.

> 
> Signed-off-by: Glauber Costa <glommer-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org>
> Signed-off-by: Anthony Liguori <aliguori-r/Jw6+rmf7HQT0dZR+AlfA@public.gmane.org>
> 
> diff --git a/hw/apic.c b/hw/apic.c
> index 2c414c1..9f1d25e 100644
> --- a/hw/apic.c
> +++ b/hw/apic.c
> @@ -938,8 +938,6 @@ static void apic_reset(void *opaque)
>      APICState *s = opaque;
>      int bsp;
>  
> -    cpu_synchronize_state(s->cpu_env);
> -
>      bsp = cpu_is_bsp(s->cpu_env);
>      s->apicbase = 0xfee00000 |
>          (bsp ? MSR_IA32_APICBASE_BSP : 0) | MSR_IA32_APICBASE_ENABLE;
> diff --git a/vl.c b/vl.c
> index 8e5d9db..c6c6a6b 100644
> --- a/vl.c
> +++ b/vl.c
> @@ -3683,10 +3683,12 @@ static void *kvm_cpu_thread_fn(void *arg)
>      while (!qemu_system_ready)
>          qemu_cond_timedwait(&qemu_system_cond, &qemu_global_mutex, 100);
>  
> +    cpu_synchronize_state(env);
> +
>      while (1) {
> +        qemu_wait_io_event(env);
>          if (cpu_can_run(env))
>              qemu_cpu_exec(env);
> -        qemu_wait_io_event(env);
>      }
>  
>      return NULL;
> @@ -3711,6 +3713,9 @@ static void *tcg_cpu_thread_fn(void *arg)
>      while (!qemu_system_ready)
>          qemu_cond_timedwait(&qemu_system_cond, &qemu_global_mutex, 100);
>  
> +    for (env = first_cpu; env != NULL; env = env->next_cpu) {
> +        cpu_synchronize_state(env);
> +    }
>      while (1) {
>          tcg_cpu_exec();
>          qemu_wait_io_event(cur_cpu);
> 

This unfortunately breaks upstream KVM (Linux fails to detect the tiemr
IRQ properly). Is there a fix already in sight? I lost a bit overview of
all on_vcpu refactorings and kvm-register sync "simplifications".

Jan

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