Re: [PATCH] kvm-qemu: Proper vm_stop on debug events

[Anthony Liguori <anthony@codemonkey.ws>]

Jan Kiszka wrote:
> When a vcpu exits after hitting a debug exception, we have to invoke
> vm_stop(EXCP_DEBUG). But this has to take place over the io-thread.
>
> This patch introduces kvm_debug_stop_requested to signal this event, and
> it takes care that the interrupted vcpu itself goes immediately into
> stop state.
>
> Signed-off-by: Jan Kiszka <jan.kiszka@web.de>
> ---
>  qemu/qemu-kvm.c |    9 ++++++++-
>  1 file changed, 8 insertions(+), 1 deletion(-)
>
> Index: b/qemu/qemu-kvm.c
> ===================================================================
> --- a/qemu/qemu-kvm.c
> +++ b/qemu/qemu-kvm.c
> @@ -58,6 +58,8 @@ pthread_t io_thread;
>  static int io_thread_fd = -1;
>  static int io_thread_sigfd = -1;
>  
> +static int kvm_debug_stop_requested;
> +
>   

Why use this instead of just keying off of exception_index == EXCP_DEBUG?

>  static inline unsigned long kvm_get_thread_id(void)
>  {
>      return syscall(SYS_gettid);
> @@ -517,6 +519,10 @@ int kvm_main_loop(void)
>              qemu_system_powerdown();
>          else if (qemu_reset_requested())
>  	    qemu_kvm_system_reset();
> +	else if (kvm_debug_stop_requested) {
> +	    kvm_debug_stop_requested = 0;
> +	    vm_stop(EXCP_DEBUG);
> +	}
>      }
>  
>      pause_all_threads();
> @@ -529,7 +535,8 @@ static int kvm_debug(void *opaque, int v
>  {
>      CPUState *env = cpu_single_env;
>  
> -    env->exception_index = EXCP_DEBUG;
> +    kvm_debug_stop_requested = 1;
> +    vcpu_info[vcpu].stopped = 1;
>   

This isn't quite right.  In the very least, you need to set stopping = 0 
and signal on the qemu_pause_cond.  Thinking it through more though, a 
breakpoint should stop all VCPUs, right?

vm_stop(EXCP_DEBUG) will actually do this.  It invokes the 
vm_state_notify callbacks and the io-thread registers one.  I think you 
should probably just issue vm_stop(EXCP_DEBUG) from kvm_debug.

Regards,

Anthony Liguori

>      return 1;
>  }
>  
> --
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